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1

15N NATURAL ABUNDANCE AND 15N LABELLING STUDIES IN FOREST ECOSYSTEMS  

EPA Science Inventory

The relative amounts of the two stable isotopes of Nitrogen (N), 15N, and N, vary predictably in soils and plant tissues of forests and other non-cultivated ecosystems. light fractionations, or discriminations against the heavier N isotope, that can occur as N cycles through vege...

2

Indirectly detected heteronuclear correlation solid-state NMR spectroscopy of naturally abundant 15N nuclei.  

PubMed

Two-dimensional indirectly detected through-space and through-bond (1)H{(15)N} solid-state NMR experiments utilizing fast magic angle spinning (MAS) and homonuclear multipulse (1)H decoupling are evaluated. Remarkable efficiency of polarization transfer can be achieved at a MAS rate of 40 kHz by both cross-polarization and INEPT, which makes these methods applicable for routine characterizations of natural abundance solids. The first measurement of 2D (1)H{(15)N} HETCOR spectrum of natural abundance surface species is also reported. PMID:24287060

Althaus, Stacey M; Mao, Kanmi; Stringer, John A; Kobayashi, Takeshi; Pruski, Marek

2014-01-01

3

Characteristics of the Nitrogen Cycle in Southern Everglades Marshes: 15N Tracer and Natural Abundance Experiments  

NASA Astrophysics Data System (ADS)

An in situ mesocosm experiment was conducted in the freshwater marshes of the Southern Everglades. The object of this experiment was to compare 15N natural abundances to N-cycling in mesocosms amended with 15N tracer. The 15N tracer technique allowed us to isolate the flows of N among various ecosystem components. Six mesocosms (2 m2) were deployed in the oligotrophic P-limited marshes of the C-111 basin. The experiment ran for a period of 21 days with sampling occurring at t=0, 5, 10, 20, 30min, 1, 3, and 6hr on the first day and subsequently on days 2, 3, 5, 9, 15, and 21. Periphyton, soil, macrophytes (Cladium jamaicense), and consumers (Gambusia holbrooki) were collected. The isotopic tracer added to the enriched mesocosms possessed a \\delta 15N value of 300\\permil. Isotopic analysis was completed on a Finnigan Delta C EA-IRMS. All ecosystem components showed tracer uptake except for the soil, which remained at natural abundance levels throughout the experiment. Periphyton showed both the most rapid and the greatest N tracer uptake with an increase of 8.7\\permil, 5 minutes after tracer addition and a maximum \\delta 15N value of 197.93\\permil at day 3. This experiment demonstrated that at study sites with low nitrate concentrations (\\approx3\\muM) a 300 permil dosing rate of 15N labled Ca(NO3)2 (\\+98% 15N) would not increase mesocosm nitrate above ambient concentrations and would provide a significant isotopic signal to track fluxes of N among ecosystem components. In addition, an experiment was conducted in the same region to determine natural abundance values for ecosystem components at both near-canal and downstream sites. All components sampled at the near-canal site had significantly heavier nitrogen isotopic values than did the downstream components (\\delta 15N 7.44\\permil \\pm2.11 and 2.01\\permil \\pm1.44 respectively); suggesting the Southern Everglades marsh is acting as a sink for canal-borne DIN and a source for "new" marsh derived DON.

Wozniak, J. R.; Anderson, W. T.; Childers, D. L.; Madden, C. J.; Rudnick, D.

2004-12-01

4

15 N natural abundance in plants of the Amazon River floodplain and potential atmospheric N 2 fixation  

Microsoft Academic Search

Summary The15N natural abundance values of various Amazon floodplain (várzea) plants was investigated. Samples of young leaf tissues were collected during three different periods of the river hydrography (low water, mid rising water and high water) and during one period in the Madeira River (high water). A large variation of15N abundance was observed, both among the different plant types and

L. A. Martinelli; R. L. Victoria; P. C. O. Trivelin; A. H. Devol; J. E. Richey

1992-01-01

5

?15N natural abundance in permafrost soil indicates impact of fire on nitrogen cycle.  

PubMed

The impact of fire on the nitrogen (N) cycle of natural ecosystems is arguable. Here we report and interpret an observation from boreal ecosystems in the Lena River basin, Sakha Republic (Yakutia), Russian Federation. Different types of permafrost soil (0-30 cm depth) were sampled along transects (60-150 m length) from the forest edge towards the centre of four separate thermokarst depressions under grassland. The average values of ?(15)N were remarkably similar within three transects, but differed systematically between them. Three findings point towards fire being the cause of the observed pattern. First, the spatial extent of systematic differences in soil ?(15)N coincides with the extent of typical fire scars in the region. Second, soil enrichment in (15)N is larger in the proximity of settlements, where fire is generally more frequent than in more remote places. Third, there is a significant positive correlation between ?(15)N values and the ratio of black C to total N. These findings point towards fire having a marked impact on soil ?(15)N and, accordingly, on the N cycle of this cold and dry ecosystem. PMID:21290453

Conen, Franz; Yakutin, Mikhail V; Puchnin, Alexander N; Leifeld, Jens; Alewell, Christine

2011-03-15

6

Rapid, storm-induced changes in the natural abundance of sup 15 N in a planktonic ecosystem, Chesapeake Bay, USA  

SciTech Connect

Samples of dissolved inorganic nitrogen (DIN), particulate nitrogen (PN), and two species of zooplankton were collected during two north-south transects of the Chesapeake Bay in the autumn of 1984 (27-28 September and 3-5 October). During the first transect, the natural abundance of {sup 15}N ({delta} {sup 15}N) in the major dissolved and planktonic pools of nitrogen suggested that the {delta}{sup 15}N of PN was largely determined by isotopic fractionation during uptake of NH{sub 4}{sup +} by phytoplankton. Averaged over the transect as a whole, the {delta}{sup 15}N of the herbivorous calanoid copepod Acartia tonsa was 4.1% higher than that of the PN, while the {delta}{sup 15}N of the carnivorous ctenophore Mnemiopsis leidyi was 6.4% higher than that of the PN. In the interval between the two transects, storm-induced mixing of the water column resulted in the injection of NH{sub 4}{sup +} into the surface layer of the bay. In combination with ancillary physical, chemical, and biological data, these changes in {delta}{sup 15}N provided estimates of the isotopic fractionation factor for NH{sub 4}{sup +} uptake by phytoplankton ({alpha} = 1.0065-1.0080) as well as the turnover time of nitrogen in Acartia tonsa (6.0-9.6 days). Despite the changes in {delta}{sup 15}N observed during this cruise, the relative distribution of {sup 15}N between trophic levels was preserved: during the second transect, the difference in {delta}{sup 15}N between Acartia tonsa and PN was 3.6%, and the difference in {delta}{sup 15}N between Mnemiopsis leidyi and PN was 7.3%. These results demonstrate that the natural abundance of {sup 15}N can change dramatically on a time scale of days, and that time-series studies of the natural abundance of {sup 15}N can be a useful complement to studies using tracer additions of {sup 15}N to document nitrogen transformations in planktonic ecosystems.

Montoya, J.P.; McCarthy, J.J. (Harvard Univ., Cambridge, MA (United States)); Horrigan, S.G. (State Univ. of New York, Stony Brook (United States))

1991-12-01

7

The structure of sarcomejine: an application of long-range (1)H-(15)N correlation at natural abundance.  

PubMed

A new 4(1H)-quinolinone alkaloid, sarcomejine (1), has been isolated from the bark of Sarcomelicope megistophylla. Its structure has been elucidated on the basis of MS and NMR data and especially with a long-range (1)H-(15)N correlation NMR spectrum at natural abundance. PMID:10924187

Fokialakis, N; Magiatis, P; Skaltsounis, A L; Tillequin, F; Sévenet, T

2000-07-01

8

Estimates of N 2 -fixation from variation in the natural abundance of 15 N in Sonoran desert ecosystems  

Microsoft Academic Search

The 15N abundance of tissues of five Prosopis specimens at our primary study site (a Prosopis woodland at Harper's Well in the Sonoran desert of Southern California) was determined over two growing seasons 1980 and 1981. The 15N abundance of soil and of tissues of presumed non-N2-fixing (control) plants was also measured. Prosopis tissues were significantly lower in 15N than

G. Shearer; D. H. Kohl; R. A. Virginia; B. A. Bryan; J. L. Skeeters; E. T. Nilsen; M. R. Sharifi; P. W. Rundel

1983-01-01

9

Natural-abundance 15N NMR studies of Turkey ovomucoid third domain. Assignment of peptide 15N resonances to the residues at the reactive site region via proton-detected multiple-quantum coherence  

NASA Astrophysics Data System (ADS)

Heteronuclear two-dimensional 1H{ 15N} multiple-quantum (MQ) spectroscopy has been applied to a protein sample at natural abundance: ovomucoid third domain from turkey ( Meleagris gallopavo), a serine proteinase inhibitor of 56 amino acid residues. Peptide amide 1H NMR assignments obtained by two-dimensional 1H{ 1H} NMR methods (R. Krishnamoorthi and J. L. Markley, unpublished data) led to identification of the corresponding 1H{ 15N} MQ coherence cross peaks. From these, 15N NMR chemical shifts were determined for several specific backbone amide groups of amino acid residues located around the reactive site region of the inhibitor. The results suggest that amide 15N chemical shifts, which are readily obtained in this way, may serve as sensitive probes for conformational studies of proteins.

Ortiz-Polo, Gilberto; Krishnamoorthi, R.; Markley, John L.; Live, David H.; Davis, Donald G.; Cowburn, David

10

/sup 15/N natural abundance in warm-core rings of the Gulf Stream: studies of the upper-ocean nitrogen cycle  

SciTech Connect

An extensive study of /sup 15/N natural abundance in particulate organic nitrogen (PON) from warm-core rings of the Gulf Stream was carried out to test its use as an in situ tracer of the marine nitrogen cycle. Ring 82-B exhibited large temporal changes in the delta/sup 15/N of PON. It was found that delta/sup 15/N values for euphotic zone PON were low in April before stratification and higher in June after stratification had occurred. Below 400 meters, in the permanent thermocline, the change was opposite going from very high values to ones similar to those at the surface. Examination of vertical profiles for delta/sup 15/N in the upper 200 meters demonstrated that in stratified waters a delta/sup 15/N minimum for PON occurs with both the top of the nitracline and a maximum in PON concentration. Often a minimum in C/N ratio also occurs at the depth of the delta/sup 15/N minimum. A mathematical model of nitrogen flux into and out of the euphotic zone and associated isotopic fractionation qualitatively reproduced the observed patterns for the delta/sup 15/N of PON, PON concentration and NO/sub 3//sup -/ concentration. Levels of PON increased as a result of either increasing NO/sub 3//sup -/ flux into the euphotic zone or increasing the residence time of PON in the euphotic zone. These results lend general support to current views regarding the nature and significance of the vertical fluxes of nitrogen in the upper-ocean and the hypotheses presented concerning the factors which control the delta/sup 15/N of PON.

Altabet, M.A.

1984-01-01

11

Determination of the natural abundance delta15N of nortropane alkaloids by gas chromatography-isotope ratio mass spectrometry of their ethylcarbamate esters.  

PubMed

An important route for the detoxification of tropane alkaloids involves N-demethylation to the nor-compounds followed by further degradation. In order to study the mechanisms of the pertinent reactions, a suitable means to determine the isotope ratios of the substrates and products is required. However, the polarity and functionality of the nortropane compounds makes their analysis as free bases difficult. A method is described which allows both the quantification of nortropane alkaloids and the determination of their natural abundance delta(15)N values. The protocol exploits the derivatisation of the alkaloids by reaction with ethyl chloroformate in aqueous medium and the quantitative extraction of the ensuing ethylcarbamate esters. The improved chromatographic properties of these derivatives gives ample separation of the isomeric nortropine and norpseudotropine for measurement of their delta(15)N (per thousand) values by isotope ratio mass spectrometry interfaced to gas chromatography. Adequate separation could not be achieved with the underivatised compounds. Repeatability and precision are sufficient to allow differences in the delta(15)N values (Deltadelta(15)N) > 0.8 per thousand to be measured, with a standard deviation routinely approximately 0.3 per thousand. The methodology has been tested by determining the changes in the delta(15)N values of nortropine and norpseudotropine during degradation by cell suspension cultures of a Pseudomonas strain expressing a specific capacity for tropine catabolism. The precision and reproducibility are shown sufficient to allow the evolution of the delta(15)N values to be followed during the fermentation. PMID:20024532

Kosieradzka, Katarzyna; Tea, Illa; Gentil, Emmanuel; Robins, Richard J

2010-02-01

12

Effects of four different restoration treatments on the natural abundance of (15)n stable isotopes in plants.  

PubMed

?(15)N signals in plant and soil material integrate over a number of biogeochemical processes related to nitrogen (N) and therefore provide information on net effects of multiple processes on N dynamics. In general little is known in many grassland restoration projects on soil-plant N dynamics in relation to the restoration treatments. In particular, ?(15)N signals may be a useful tool to assess whether abiotic restoration treatments have produced the desired result. In this study we used the range of abiotic and biotic conditions provided by a restoration experiment to assess to whether the restoration treatments and/or plant functional identity and legume neighborhood affected plant ?(15)N signals. The restoration treatments consisted of hay transfer and topsoil removal, thus representing increasing restoration effort, from no restoration measures, through biotic manipulation to major abiotic manipulation. We measured ?(15)N and %N in six different plant species (two non-legumes and four legumes) across the restoration treatments. We found that restoration treatments were clearly reflected in ?(15)N of the non-legume species, with very depleted ?(15)N associated with low soil N, and our results suggest this may be linked to uptake of ammonium (rather than nitrate). The two non-legume species differed considerably in their ?(15)N signals, which may be related to the two species forming different kinds of mycorrhizal symbioses. Plant ?(15)N signals could clearly separate legumes from non-legumes, but our results did not allow for an assessment of legume neighborhood effects on non-legume ?(15)N signals. We discuss our results in the light of what the ?(15)N signals may be telling us about plant-soil N dynamics and their potential value as an indicator for N dynamics in restoration. PMID:22645597

Temperton, Vicky M; Märtin, Lea L A; Röder, Daniela; Lücke, Andreas; Kiehl, Kathrin

2012-01-01

13

Polymeric adducts of rhodium(II) tetraacetate with aliphatic diamines: natural abundance 13C and 15N CPMAS NMR investigations.  

PubMed

Complexation properties of dimeric rhodium(II) tetracarboxylates have been utilised in chemistry, spectroscopy and organic synthesis. Particularly, the combination of these rhodium salts with multifunctional ligands results in the formation of coordination polymers, and these are of interest because of their gas-occlusion properties. In the present work, the polymeric adducts of rhodium(II) tetraacetate with flexible ligands exhibiting conformational variety, ethane-1,2-diamine, propane-1,3-diamine and their N,N'-dimethyl- and N,N,N',N'-tetramethyl derivatives, have been investigated by means of elemental analysis, (13)C CPMAS NMR, (15)N CPMAS NMR and density functional theory modelling. Elemental analysis and NMR spectra indicated the axial coordination mode and regular structures of (1 : 1)n oligomeric chains in the case of adducts of ethane-1,2-diamine, N,N'-dimethylethane-1,2-diamine N,N,N',N'-tetramethylethane-1,2-diamine and N,N,N',N'-tetramethylpropane-1,3-diamine. Propane-1,3-diamine and N,N'-dimethylpropane-1,3-diamine tended to form heterogeneous materials, composed of oligomeric (1 : 1)n chains and the additive of dirhodium units containing equatorially bonded ligands. Experimental findings have been supported by density functional theory modelling of some hypothetical structures and gauge-invariant atomic orbital calculations of NMR chemical shifts. PMID:24123364

Ja?wi?ski, Jaros?aw; Kamie?ski, Bohdan; Sadlej, Agnieszka

2013-12-01

14

Natural abundances of 15N and 13C in leaves of some N2-fixing and non-N2-fixing trees and shrubs in Syria.  

PubMed

A survey study was conducted on man-made plantations located at two different areas in the arid region of Syria to determine the variations in natural abundances of the (15)N and (13)C isotopes in leaves of several woody legume and non-legume species, and to better understand the consequence of such variations on nitrogen fixation and carbon assimilation. In the first study area (non-saline soil), the delta(15)N values in four legume species (Acacia cyanophylla,-1.73 per thousand Acacia farnesiana,-0.55 per thousand Prosopis juliflora,-1.64 per thousand; and Medicago arborea,+1.6 \\textperthousand) and one actinorhizal plant (Elaeagnus angustifolia,-0.46 to-2.1 per thousand) were found to be close to that of the atmospheric value pointing to a major contribution of N(2) fixing in these species; whereas, delta(15)N values of the non-fixing plant species were highly positive. delta(13)C per thousand; in leaves of the C3 plants were found to be affected by plant species, ranging from a minimum of-28.67 per thousand; to a maximum of-23 per thousand. However, they were relatively similar within each plant species although they were grown at different sites. In the second study area (salt affected soil), a higher carbon discrimination value (Delta(13)C per thousand) was exhibited by P. juliflora, indicating that the latter is a salt tolerant species; however, its delta(15)N was highly positive (+7.03 per thousand) suggesting a negligible contribution of the fixed N(2). Hence, it was concluded that the enhancement of N(2) fixation might be achieved by selection of salt-tolerant Rhizobium strains. PMID:20183233

Kurdali, F; Al-Shamma'a, M

2009-09-01

15

Nitrous Oxide Concentration Profiles and the Natural Abundance of 15N-N2O in a Paddy Soil During the Wheat Growing Season  

NASA Astrophysics Data System (ADS)

Soil is an important source of nitrous oxide. Significant temporal and spatial trends exist in the production and emission in paddy fields where upland winter wheat is grown. A multilevel sampling probe (0-5cm, 5-10cm, 10- 15cm, and 15-20 cm) was designed to sample the air in the soil. Changes in N2O gas concentrations in 24 profiles were studied at 10-day intervals during the wheat growing period, for 16 total sampling dates. Surface fluxes were studied simultaneously from 24 field plots (4m x 5m). The natural abundance of 15N2O in eight profiles was measured three times during the wheat season by using a MAT 253 isotope mass chromatograph. Dynamic soil ammonium and nitrate concentrations in the plough layer and profile soil redox potential were also monitored throughout the wheat season. We present the first in situ data of such gradients over time for a paddy field seeded with wheat. Results indicate that N2O was produced at the lower levels of 10cm-15cm and 15-20cm, and that denitrification was the dominant process for N2O production even under the aerobic wheat cropping condition. N2O at 10-15cm depth has the most negative natural abundance of 15N. Profiles with higher concentrations of soil nitrate give more negative values of natural abundance of 15N2O. The lower levels of 10cm-15cm and 15cm-20cm give the highest concentrations during the whole wheat growing season. The maximum concentration of 14.8 mL m-3 and the maximum flux of 126 micro g N m-2 h-1 were found in January and April, respectively. N2O concentrations are significantly correlated between all layers over time. Spatial variations exist in N2O emissions and concentration profiles, but temporal variations are greater. The N2O emission peaks did not always coincide with soil concentration peaks. These results suggest that to understand the underlying processes, we need to measure both surface fluxes and soil concentrations simultaneously. This research was supported by the Office of Science (BER), US Department of Energy, Grant No. DE-FG02- 04ER63913, and the Institute of Soil Sciences, Chinese Academy of Sciences.

Xiong, Z.; Khalil, A. M.; Shearer, M.; Butenhoff, C.; Xing, G.

2006-12-01

16

Natural abundance 15N CP/MAS of nylons and aramids: A sensitive technique for examining crystalline composition and conformation in solid polyamides  

NASA Astrophysics Data System (ADS)

We have examined a variety of polyamides and aramids using natural abundance 15N CP/MAS NMR. These have included commercially available A-B and AA-BB nylons, Kevlar and poly(p-benzamide) as well as a number of block and graft copolymers synthesized in our laboratory. Excellent correlation was observed between the type of crystalline form adopted by polyamides (alpha and gamma modifications) and the chemical shift of the rigid amide nitrogens. Values for the two forms center around 84 ppm (relative to glycine at 0 ppm) and 88 ppm, respectively. For some samples, unexplained peaks between the two main crystalline peaks are tentatively assigned to rigid amide conformations that are not X-ray active but are seen by NMR. Aramids show similar complexity. Block and graft copolymers display characteristic peaks for composition (aryl vs alkyl nitrogen substituents) and for conformation and crystallinity.

Powell, Douglas G.; Sikes, Allison M.; Mathias, Lon J.

1988-09-01

17

Leaf allocation patterns and 13C and 15N natural abundances of tropical lianas (Passiflora sp.) as dependent on external climbing support.  

PubMed

The transformation from self-supporting lianas to host-supported climbing lianas is related to re-allocation of biomass and nutrients among plant organs. Therefore, first, variations in leaf mass per area (LMA), leaf carbon and nitrogen allocation and (13)C and (15)N natural abundances were analysed among three tropical Passiflora species (P. edulis, P. ligularis, and P. tripartita) in a greenhouse study. Second, the influence of a climbing support was considered for each species and parameter. P. ligularis leaves were most enriched in (13)C in both treatments when compared with the other two species. This enrichment was caused by a high LMA, which is related to a high internal resistance to CO(2) diffusion. For P. edulis and P. tripartita, ?(13)C was additionally increasing with nitrogen content per area. Generally, there were no differences when considering carbon and nitrogen allocation to leaves of host-supported and self-supporting lianas. The only hints towards increased investment into leaves after the transition from self-supporting to host-supported stages could be seen by a trend to increased leaf areas and masses. ?(13)C values of supported P. edulis or P. tripartita plants were significantly increasing faster than those of non-supported plants once the interactions of leaf mass or nitrogen content per area were accounted for. Hence, the offer of a climbing support had only a minor impact on ?(13)C or ?(15)N values in vitro, but this could be different with increasing age of lianas in vivo. PMID:23134439

Werth, Martin; Spiegel, Ann-Kathrin; Kazda, Marian

2013-01-01

18

Estimates of N2 Fixation Based on Differences in the Natural Abundance of 15N in Nodulating and Nonnodulating Isolines of Soybeans 1  

PubMed Central

Estimates of the contribution of biologically fixed N to the total N of nodulating soybeans (Glycine max (L) Merrill, variety Harosoy) grown under a variety of conditions were made from: (a) differences in N yield between nodulating and nonnodulating isolines; and (b) differences in 15N abundance between the two isolines. For plants grown in a greenhouse in nutrient-poor soil, both estimates showed a high level of N2 fixation; from 58 to 89% N fixed by differences in N yield and from 51 to 95% by differences in 15N abundance. Decreasing contributions of fixed N were estimated by both methods with increasing levels of added NO3?. Results of field experiments carried out over two years on an unamended highly fertile midwestern soil showed a modest level of N2 fixation by both methods (7.3 to 51% by differences in N yield, and 5.4 to 46% by differences in 15N abundance). When the soil was amended with ground corn cobs, both methods showed higher contributions of fixed N. The two methods of estimating N2 fixation gave similar results. Both appear to be semiquantitative and the standard errors of the estimates were about the same (6% on the average).

Kohl, Daniel H.; Shearer, Georgia; Harper, James E.

1980-01-01

19

Estimates of dry and wet deposition using tissue N contents and 15N natural abundance in epilithic mosses in atmospheric NHy-dominated areas  

NASA Astrophysics Data System (ADS)

Measurement of dry N deposition by physical methods is time-consuming because it is usually difficult to measure directly. In this study, an alternative approach has successfully been proposed by coupling isotopic ratios with tissue N contents of epilithic mosses. The method is to use moss N contents to quantitatively estimate total N (TN) deposition and then to use 15N natural abundance in mosses to discriminate dry and wet deposition in atmospheric NHy-dominated areas (NHy/TN > 0.75). On the basis of the isotopic balance between atmospheric NHy and moss tissue N and the correlation between atmospheric NHy concentrations and their isotopes, both wet and dry N deposition can be estimated. By the approach, we have estimated rainwater ammonium concentrations and contribution percentage of wet deposition to total N deposition (fwet) in some areas of southern China. The results indicated that rainwater ammonium concentrations increased relative to those reported previously in most cities, owing to stronger anthropogenic activity. The fwet values estimated in most sites were found to be slightly higher than those reported, because faster transformation rates due to higher SO2 emission later in acid rain areas of southern China favored deposition in the form of wet deposition instead of dry deposition. The largest uncertainty of the approach comes from the influence of NOx in the atmosphere, and thus it cannot be used in areas where NOx deposition is high. The presented isotopic approach represents a new application of moss biomonitoring for estimating atmospheric N deposition in NHy-dominated areas.

Xiao, Hua-Yun; Liu, Cong-Qiang

2011-02-01

20

Comparative structural analysis of 1-methyladenosine, 7-methylguanosine, ethenoadenosine and their protonated salts IV: 1H, 13C, and 15N NMR studies at natural isotope abundance.  

PubMed Central

The 1H, 13C, and 15N NMR spectra of neutral and protonated forms of the nucleosides 1-methyladenosine (m1A), 7-methylguanosine (m7G) and ethenoadenosine (EA), as a model compound, have been analyzed in order to assign the site of protonation in m1A and m7G. Protonation of these nucleosides occurs in the pyrimidine ring of m1A and EA and in the imidazole ring of m7G, with the charge being distributed rather than localized. Structural differences for both m1A and m7G were observed in solution and compared with those existing in the crystal state of monomers as well as in tRNA where these nucleosides occur quite often. The protonated nucleoside structures in solution compared favorably in sugar pucker and glycosidic bond conformations with x-ray crystallographic data. Methyl group carbon chemical shifts of the protonated mononucleosides corresponded to those of the methyls of the respective nucleosides in native tRNA structures. Therefore, the tRNA methyl group carbon chemical shifts are indicative of fully protonated nucleosides in the native, three dimensional structure of the nucleic acid. Images

Sierzputowska-Gracz, H; Gopal, H D; Agris, P F

1986-01-01

21

Determination of 15N Abundance in Nanogram Pools of NO3- and NO2- by Denitrification Bioassay and Mass Spectrometry  

PubMed Central

Suspensions of two strains of Pseudomonas aeruginosa (ON12 and ON12-1) were used to reduce NO3- and NO2-, respectively, to N2O. The evolved N2O was quantified by gas chromatography with electron capture detection, and the 15N abundance was determined by mass spectrometry with a special inlet system and triple-collector detection. Sample gas containing unknown N2O pools as small as 0.5 ng of N was analyzed by use of a spike technique, in which a reference gas of N2O of natural 15N abundance was added to obtain enough total N for the mass spectrometer. In NO3- or NO2- pools, the 15N abundance could be determined in samples as small as approximately 3.5 ng of N. No cross-contamination took place between the NO3- and NO2- pools. The excellent separation of NO3- and NO2- pools, small sample size required, and low contamination risk during N2O analysis offer great advantages in isotope studies of inorganic N transformations by, e.g., nitrifying or denitrifying bacteria in the environment.

H?jberg, Ole; Johansen, Henrik Saaby; S?rensen, Jan

1994-01-01

22

Leaf 15 N abundance of subarctic plants provides field evidence that ericoid, ectomycorrhizal and non-and arbuscular mycorrhizal species access different sources of soil nitrogen  

Microsoft Academic Search

The natural abundance of the nitrogen isotope 15, d15N, was analysed in leaves of 23 subarctic vascular plant species and two lichens from a tree-line heath at 450 m altitude and a fellfield at 1150 m altitude close to Abisko in N. Sweden, as well as in soil, rain and snow. The aim was to reveal if plant species with

Anders Michelsen; Inger K. Schmidt; Sven Jonasson; Chris Quarmby; Darren Sleep

1996-01-01

23

15 N isotope biogeochemistry and natural denitrification process in groundwater: Application to the chalk aquifer of northern France  

Microsoft Academic Search

The use of 15 N natural isotope tracing in an aquifer contained within chalk rocks in northern France indicates that, under certain hydrogeological conditions, major denitrification occurs. At the boundary where the aquifer becomes confined, the nitrate concentrations decrease in the direction of groundwater flow accompanied by an exponential increase in 15 N (expressed in 15 N ) of the

André Mariotti; Alain Landreau; Béatrice Simon

1988-01-01

24

A new approach to determining the content and 15N abundance of total dissolved nitrogen in aqueous samples: TOC analyser-QMS coupling.  

PubMed

The standard method for determining the 15N abundance of total dissolved nitrogen (TDN) in aqueous samples (e.g., soil leachate, sewage, urine) is currently Kjeldahl digestion followed by steam distillation or diffusion to isolate the ammonium, and then 15N measurement using IRMS. However, this technique is both time-consuming and laborious. One way of overcoming these disadvantages could be to couple a TOC analyser to determine the TDN with a sufficient quadrupole MS to determine the 15N abundance. The high TOC analyser (Elementar Analysensysteme Hanau, Germany), which catalytically oxidises the sample's total nitrogen with a high, constant yield to nitrogen monoxide (NO), appeared particularly suitable. The quadrupole-MS ESD 100 (InProcess Instruments Bremen, Germany) proved to be a suitable mass spectrometer for the 15N determination of NO. This combination of instruments was found to provide a workable method in numerous measurements of standard and actual samples. The detection limit concerning the N amount required per analysis is 2 microg, corresponding to an N concentration of 0.7 mg/l in a maximum sample volume of 3ml. Depending on the N concentration, 15N abundances starting from 0.5 at.% can be measured with the required precision of better than 3% (simple standard deviation). For example, measuring the abundance of 0.5 at.% requires about 50 microg N, whereas for 1 at.% or more only about 5 microg N is needed per analysis. PMID:12725425

Russow, R; Kupka, H J; Götz, A; Apelt, B

2002-12-01

25

Determination of the abundance of delta15N in nitrate ion in contaminated groundwater samples using an elemental analyzer coupled to a mass spectrometer.  

PubMed

A rapid method for measuring the delta15N of nitrate ion in water samples using an isotope ratio mass spectrometer coupled to an elemental analyzer system (EA-MS) was investigated. The water should be removed from the analytical sample before measurement with this system. We investigated the application of a super-absorbent polymer resin powder to various water samples. Each 1 mg of polymer resin powder can absorb about 50-100 mg of solution depending on the concentrations of major ions. Only samples which contain more than 100 mg l(-1) of nitrate-nitrogen are suitable to be absorbed by the polymer resin for the determination of delta15N of nitrate. Preconcentration by rotary evaporation was necessary for dilute samples but the temperature should be kept below 60 degrees C. The polymer resin (about 8 mg) containing the nitrate was directly analyzed using an EA-MS after being oven-dried at 80 degrees C. Good accuracy (precision +/- 0.3%) for delta15N measurements of nitrate-nitrogen in a sample without any isotope fractionation effects during pre-treatment was observed. Results for delta15N of nitrate in contaminated groundwater samples collected in the spring at a tea plantation area in Shizuoka, Japan, were from 9.8 to 10.6%, which were close to the delta15N abundance in organic fertilizers. PMID:11478634

Ogawa, Y; Nishikawa, M; Nakasugi, O; Ii, H; Hirata, T

2001-07-01

26

Search for basic relationships between "molecular size" and "chemical structure" of aquatic natural organic matter--answers from 13C and 15N CPMAS NMR spectroscopy.  

PubMed

To investigate the structural composition of natural organic matter (NOM), a 3-step micro- and ultrafiltration procedure was applied to 3 surface waters from southern Germany, and fractions from all filtration steps were collected. The NOM was characterized using solid-state 13C and 15N nuclear magnetic resonance (NMR) techniques. Routine integration of the 13C NMR spectra and extended data analysis procedures were carried out for a quantitative comparison of the structural components as well as for the elucidation of structural fractionation patterns. A common feature of the large molecular size fractions was the predominance of polysaccharide material, with the dissolved high molecular weight organics being mostly enriched in N-acetylated polysaccharides derived from microbial leftovers. Aromatic structures like lignin and tannin derivatives were most abundant in the intermediate size fraction. All membranes were found to be highly permeable for branched aliphatics, i.e. isoprenoids. Fouling layers of the ultrafiltration membrane were significantly enriched in long-chain aliphatics (lipids). Biofouling was not observed on any of the membranes. Overall, a strong interdependence between the chemical structural characteristics of NOM components and their size, shape, or interaction characteristics could be shown. The results provide the basis for a better understanding of water process technologies as treatment effectiveness is strongly dependent on the chemical composition and the "size" distribution of NOM. PMID:17959215

Lankes, Ulrich; Lüdemann, Hans-Dietrich; Frimmel, Fritz H

2008-02-01

27

Distribution of 15N Among Plant Parts of Nodulating and Nonnodulating Isolines of Soybeans 1  

PubMed Central

Differences among plant parts in the natural abundance of 15N are of interest from the point of view of developing a sampling strategy for using 15N measurements to estimate the contribution of symbiotically fixed N to N2 fixing plants, and because they reflect isotopic fractionation associated with degradation, transport, and resynthesis of N-bearing molecules. This paper reports such differences in nodulating and nonnodulating isolines of soybeans (Glycine max [L] (Merrill, variety Harosoy)) grown under several different conditions. Nodules were strikingly enriched in 15N compared to other plant parts (by an average of 8.3‰ excess 15N), and the enrichment increased with time during the growing season. 15N was much more uniformly distributed among other plant parts. Although there were significant differences among other plant parts, the maximum deviation of the 15N abundance of any plant part from that of the entire plant was about 2‰ 15N excess. The 15N abundance of the seed N was most representative of the whole plant. There were significant differences between isolines in the distribution of 15N. The distribution of 15N within plants also varied with experimental conditions. The implications of these results for estimation of N2 fixation from measurements of the natural abundance of 15N are discussed.

Shearer, Georgia; Kohl, Daniel H.; Harper, James E.

1980-01-01

28

Nitrate reductase 15N discrimination in Arabidopsis thaliana, Zea mays, Aspergillus niger, Pichea angusta, and Escherichia coli  

PubMed Central

Stable 15N isotopes have been used to examine movement of nitrogen (N) through various pools of the global N cycle. A central reaction in the cycle involves the reduction of nitrate (NO?3) to nitrite (NO?2) catalyzed by nitrate reductase (NR). Discrimination against 15N by NR is a major determinant of isotopic differences among N pools. Here, we measured in vitro 15N discrimination by several NRs purified from plants, fungi, and a bacterium to determine the intrinsic 15N discrimination by the enzyme and to evaluate the validity of measurements made using 15N-enriched NO?3. Observed NR isotope discrimination ranged from 22 to 32‰ (kinetic isotope effects of 1.022–1.032) among the different isozymes at natural abundance 15N (0.37%). As the fractional 15N content of substrate NO?3 increased from natural abundance, the product 15N fraction deviated significantly from that expected based on substrate enrichment and 15N discrimination measured at natural abundance. Additionally, isotopic discrimination by denitrifying bacteria used to reduce NO?3 and NO?2 in some protocols became a greater source of error as 15N enrichment increased. We briefly discuss potential causes of the experimental artifacts with enriched 15N and recommend against the use of highly enriched 15N tracers to study N discrimination in plants or soils.

Carlisle, Eli; Yarnes, Chris; Toney, Michael D.; Bloom, Arnold J.

2014-01-01

29

Nicotine, acetanilide and urea multi-level2H-,13C- and15N-abundance reference materials for continuous-flow isotope ratio mass spectrometry  

USGS Publications Warehouse

Accurate determinations of stable isotope ratios require a calibration using at least two reference materials with different isotopic compositions to anchor the isotopic scale and compensate for differences in machine slope. Ideally, the S values of these reference materials should bracket the isotopic range of samples with unknown S values. While the practice of analyzing two isotopically distinct reference materials is common for water (VSMOW-SLAP) and carbonates (NBS 19 and L-SVEC), the lack of widely available organic reference materials with distinct isotopic composition has hindered the practice when analyzing organic materials by elemental analysis/isotope ratio mass spectrometry (EA-IRMS). At present only L-glutamic acids USGS40 and USGS41 satisfy these requirements for ??13C and ??13N, with the limitation that L-glutamic acid is not suitable for analysis by gas chromatography (GC). We describe the development and quality testing of (i) four nicotine laboratory reference materials for on-line (i.e. continuous flow) hydrogen reductive gas chromatography-isotope ratio mass-spectrometry (GC-IRMS), (ii) five nicotines for oxidative C, N gas chromatography-combustion-isotope ratio mass-spectrometry (GC-C-IRMS, or GC-IRMS), and (iii) also three acetanilide and three urea reference materials for on-line oxidative EA-IRMS for C and N. Isotopic off-line calibration against international stable isotope measurement standards at Indiana University adhered to the 'principle of identical treatment'. The new reference materials cover the following isotopic ranges: ??2Hnicotine -162 to -45%o, ??13Cnicotine -30.05 to +7.72%, ?? 15Nnicotine -6.03 to +33.62%; ??15N acetanilide +1-18 to +40.57%; ??13Curea -34.13 to +11.71%, ??15Nurea +0.26 to +40.61% (recommended ?? values refer to calibration with NBS 19, L-SVEC, IAEA-N-1, and IAEA-N-2). Nicotines fill a gap as the first organic nitrogen stable isotope reference materials for GC-IRMS that are available with different ??13N values. Comparative ??13C and ??15N on-line EA-IRMS data from 14 volunteering laboratories document the usefulness and reliability of acetanilides and ureas as EA-IRMS reference materials.

Schimmelmann, A.; Albertino, A.; Sauer, P. E.; Qi, H.; Molinie, R.; Mesnard, F.

2009-01-01

30

Hair protein and amino acid 13C and 15N abundances take more than 4 weeks to clearly prove influences of animal protein intake in young women with a habitual daily protein consumption of more than 1 g per kg body weight.  

PubMed

A high protein or meat intake might be a risk factor for metabolic disorders. Stable isotopic abundances (SIA) of hair can be used as biomarkers for animal protein intake due to characteristic isotopic patterns of food proteins. We investigated if an additional meat intake (M, 200 g pork fillet/day) or an omission of meat and meat products (NOM) can influence the natural (15)N and (13)C SIA within 4 weeks in hair and plasma of young women. The daily protein intake (means +/- SD) was 1.40 +/- 0.29, 2.25 +/- 0.35, and 1.15 +/- 0.26 g/kg at baseline, during M, and during NOM, respectively. At baseline the animal protein intake correlated with bulk SIA of hair ((15)N: R(2) = 0.416; (13)C: R(2) = 0.664; n = 14). However, isotope ratio mass spectrometry (IRMS) analyses have not shown that hair and plasma SIA were changed significantly after M or NOM. Possible reasons were discussed. Urinary SIA were significantly lower after M than after NOM ((15)N: p = 0.039; (13)C: p = 0.006) and close to those of pork fillet. Characteristic patterns of SIA were measured in individual amino acids (AA) by gas chromatography/combustion isotope ratio mass spectrometry (GC/C/IRMS). The results confirmed considerable differences in SIA between AA (delta(15)N, up to 22 per thousand; delta(13)C, up to 31 per thousand). Plots of (15)N versus (13)C abundances in hair revealed characteristic differences between indispensable and dispensable AA. The intervention-dependent changes of AA-specific SIA were not as clear as expected. Although the AA-specific SIA may reveal more detailed characteristics of physiological conditions, further methodological research is required. We suggest that the SIA of leucine can be potential markers of protein intake. The reliability of SIA as biomarkers of protein intake still have to be tested in longer lasting intervention studies in humans. The results may have implications in the assessment for possible benefits and risks of protein consumption. PMID:19603474

Petzke, Klaus J; Lemke, Susen

2009-08-30

31

Grass species influence on plant N uptake - Determination of atmospheric N deposition to a semi-natural peat bog site using a 15N labelling approach  

NASA Astrophysics Data System (ADS)

Large areas of natural peat bogs in Northwestern Germany have been converted to arable land and were subjected to draining and peat cutting in the past. The few protected peatland areas remaining are affected by high nitrogen (N) deposition. Our study site - a moderately drained raised bog - is surrounded by highly fertilized agricultural land and livestock production. In this study, we used a 15N pool dilution technique called 'Integrated Total Nitrogen Input' (ITNI) to quantify annual deposition of atmospheric N into biomonitoring pots over a two-year period. Since it considers direct N uptake by plants, it was expected to result in higher N input than conventional methods for determination of N deposition (e.g. micrometeorological approaches, bulk N samplers). Using Lolium multiflorum and Eriophorum vaginatum as monitor plants and low, medium and high levels of fertilization, we aimed to simulate increasing N deposition to planted pots and to allocate airborne N after its uptake by the soil-plant system in aboveground biomass, roots and soil. Increasing N fertilization was positively correlated with biomass production of Eriophorum vaginatum, whereas atmospheric plant N uptake decreased and highest airborne N input of 899.8 ± 67.4 µg N d-1 pot-1 was found for low N fertilization. In contrast, Lolium multiflorum showed a clear dependency of N supply on plant N uptake and was highest (688.7 ± 41.4 µg N d-1 pot-1) for highly fertilized vegetation pots. Our results suggest that grass species respond differently to increasing N input. While crop grasses such as Lolium multiflorum take up N according to N availability, species adopted to nutrient-limited conditions like Eriophorum vaginatum show N saturation effects with increasing N supply. Total airborne N input ranged from about 24 to 66 kg N ha-1 yr-1 dependent on the used indicator plant and the amount of added fertilizer. Parallel determination of atmospheric N deposition using a micrometeorological approach complemented with bulk samplers was about 24 kg N ha-1 yr-1 during both years of experiments and was thus at the lower range of results obtained by the ITNI method. The low 15N recovery rate of about 50 % during some experiments indicated an underestimation of the applied ITNI approach, resulting in a maximum possible N uptake of twice as high as the determined N input. Most likely, the intensive agricultural land management of the surrounding areas leads to this high N deposition into the protected peatland area. As a result, increasing sensitivity of ombrotrophic vegetation with a subsequent change in plant species composition and a decline in bog-specific vegetation cannot be excluded.

Hurkuck, Miriam; Brümmer, Christian; Spott, Oliver; Flessa, Heinz; Kutsch, Werner L.

2014-05-01

32

Food Resources of Stream Macronivertebrates Determined by Natural-Abundance stable C and N Isotopes and a 15N Tracer Addition  

SciTech Connect

Trophic relationships were examined using natural-abundance {sup 13}C and {sup 15}N analyses and a {sup 15}N-tracer addition experiment in Walker Branch, a 1st-order forested stream in eastern Tennessee. In the {sup 15}N-tracer addition experiment, we added {sup 15}NH{sub 4} to stream water over a 6-wk period in early spring, and measured {sup 15}N:{sup 14}N ratios in different taxa and biomass compartments over distance and time. Samples collected from a station upstream from the {sup 15}N addition provided data on natural-abundance {sup 13}C:{sup 12}C and {sup 15}N:{sup 14}N ratios. The natural-abundance {sup 15}N analysis proved to be of limited value in identifying food resources of macroinvertebrates because {sup 15}N values were not greatly different among food resources. In general, the natural-abundance stable isotope approach was most useful for determining whether epilithon or detritus were important food resources for organisms that may use both (e.g., the snail Elimia clavaeformis), and to provide corroborative evidence of food resources of taxa for which the {sup 15}N tracer results were not definitive. The {sup 15}N tracer results showed that the mayflies Stenonema spp. and Baetis spp. assimilated primarily epilithon, although Baetis appeared to assimilate a portion of the epilithon (e.g., algal cells) with more rapid N turnover than the bulk pool sampled. Although Elimia did not reach isotopic equilibrium during the tracer experiment, application of a N-turnover model to the field data suggested that it assimilated a combination of epilithon and detritus. The amphipod Gammarus minus appeared to depend mostly on fine benthic organic matter (FBOM), and the coleopteran Anchytarsus bicolor on epixylon. The caddisfly Diplectrona modesta appeared to assimilate primarily a fast N-turnover portion of the FBOM pool, and Simuliidae a fast N-turnover component of the suspended particulate organic matter pool rather than the bulk pool sampled. Together, the natural-abundance stable C and N isotope analyses and the experimental {sup 15}N tracer approach proved to be very useful tools for identifying food resources in this stream ecosystem.

Mulholland, P. J.

2000-01-01

33

QUANTITATIVE 15N NMR SPECTROSCOPY  

EPA Science Inventory

Line intensities in 15N NMR spectra are strongly influenced by spin-lattice and spin-spin relaxation times, relaxation mechanisms and experimental conditions. Special care has to be taken in using 15N spectra for quantitative purposes. Quantitative aspects are discussed for the 1...

34

Sinks for nitrogen inputs in terrestrial ecosystems: a meta-analysis of 15N tracer field studies  

USGS Publications Warehouse

Effects of anthropogenic nitrogen (N) deposition and the ability of terrestrial ecosystems to store carbon (C) depend in part on the amount of N retained in the system and its partitioning among plant and soil pools. We conducted a meta-analysis of studies at 48 sites across four continents that used enriched 15N isotope tracers in order to synthesize information about total ecosystem N retention (i.e., total ecosystem 15N recovery in plant and soil pools) across natural systems and N partitioning among ecosystem pools. The greatest recoveries of ecosystem 15N tracer occurred in shrublands (mean, 89.5%) and wetlands (84.8%) followed by forests (74.9%) and grasslands (51.8%). In the short term (15N tracer application), total ecosystem 15N recovery was negatively correlated with fine-root and soil 15N natural abundance, and organic soil C and N concentration but was positively correlated with mean annual temperature and mineral soil C:N. In the longer term (3–18 months after 15N tracer application), total ecosystem 15N retention was negatively correlated with foliar natural-abundance 15N but was positively correlated with mineral soil C and N concentration and C: N, showing that plant and soil natural-abundance 15N and soil C:N are good indicators of total ecosystem N retention. Foliar N concentration was not significantly related to ecosystem 15N tracer recovery, suggesting that plant N status is not a good predictor of total ecosystem N retention. Because the largest ecosystem sinks for 15N tracer were below ground in forests, shrublands, and grasslands, we conclude that growth enhancement and potential for increased C storage in aboveground biomass from atmospheric N deposition is likely to be modest in these ecosystems. Total ecosystem 15N recovery decreased with N fertilization, with an apparent threshold fertilization rate of 46 kg N·ha-1·yr-1 above which most ecosystems showed net losses of applied 15N tracer in response to N fertilizer addition.

Templer, P. H.; Mack, M. C.; Chapin, F. S., III; Christenson, L. M.; Compton, J. E.; Crook, H. D.; Currie, W. S.; Curtis, C. J.; Dail, D. B.; D'Antonio, C. M.; Emmett, B. A.; Epstein, H. E.; Goodale, C. L.; Gundersen, P.; Hobbie, S. E.; Holland, K.; Hooper, D. U.; Hungate, B. A.; Lamontagne, S.; Nadelhoffer, K. J.; Osenberg, C. W.; Perakis, S. S.; Schleppi, P.; Schimel, J.; Schmidt, I. K.; Sommerkorn, M.; Spoelstra, J.; Tietema, A.; Wessel, W. W.; Zak, D. R.

2012-01-01

35

Chemical method for nitrogen isotopic analysis of ammonium at natural abundance.  

PubMed

We report a new chemical method to determine the (15)N natural abundance (?(15)N) for ammonium (NH4(+)) in freshwater (e.g., precipitation) and soil KCl extract. This method is based on the isotopic analysis of nitrous oxide (N2O). Ammonium is initially oxidized to nitrite (NO2(-)) by hypobromite (BrO(-)) using previously established procedures. NO2(-) is then quantitatively converted into N2O by hydroxylamine (NH2OH) under strongly acid conditions. The produced N2O is analyzed by a commercially available purge and cryogenic trap system coupled to an isotope ratio mass spectrometer (PT-IRMS). On the basis of a typical analysis size of 4 mL, the standard deviation of ?(15)N measurements is less than 0.3‰ and often better than 0.1‰ (3 to 5 replicates). Compared to previous methods, the technique here has several advantages and the potential to be used as a routine method for (15)N/(14)N analysis of NH4(+): (1) substantially simplified preparation procedures and reduced preparation time particularly compared to the methods in which diffusion or distillation is involved since all reactions occur in the same vial and separation of NH4(+) from solution is not required; (2) more suitability for low volume samples including those with low N concentration, having a blank size of 0.6 to 2 nmol; (3) elimination of the use of extremely toxic reagents (e.g., HN3) and/or the use of specialized denitrifying bacterial cultures which may be impractical for many laboratories. PMID:24654992

Liu, Dongwei; Fang, Yunting; Tu, Ying; Pan, Yuepeng

2014-04-15

36

13C/12C and 15N/14N Isotope Analysis to Characterize Natural Degradation of Atrazine: Evidence from Parent and Daughter Compound Values  

NASA Astrophysics Data System (ADS)

The mobile and still herbicidal metabolites desethylatrazine (DEA) and desisopropylatrazine (DIA) are frequently detected together with its parent compound atrazine (Atz) in the aquatic environment. Interpretation of their transformation state is often difficult with current methods, which are mainly measuring concentrations. Alternatively, compound specific isotope analyses (CSIA) has become a novel tool to detect degradation processes of contaminants in groundwater. The aim of our study was to investigate on the lab scale 13C/12C and 15N/14N isotope trends in parent and daughter compounds associated with different degradation scenarios of atrazine likely to occur in the environment. Thus atrazine was dealkylated with (i) permanganate and (ii) the bacterium Rhodococcus sp. NI86/21. In both transformations, 13C/12C ratios of atrazine increased strongly (epsilon carbon/permanganate = -4.6 ± 0.6 ‰ and epsilon carbon/Rhodoccoccus = -3.8 ± 0.2 ‰) whereas nitrogen isotope fractionation was small. 13C/12C ratios of DEA showed the following trends. (i) When DEA was formed as only product (Atz + permanganate) 13C/12C remained constant, close to the initial value of Atz. (ii) When DEA was formed together with deisopropylatrazine (biodegradation of Atz) 13C/12C increased, but only within 2‰. (iii) When DEA and DIA was further biodegraded, 13C/12C increased for both metabolites up to 9‰. Thus strong enrichment of 13C/12C in the metabolites in comparison to Atz can give strong testimony for further breakdown of the metabolite.

Elsner, Martin; Meyer, Armin

2013-04-01

37

Natural abundance nitrogen-15 nuclear magnetic resonance spectral studies on selected donors  

NASA Astrophysics Data System (ADS)

The natural abundance 15N-NMR chemical shifts of selected aliphatic amines, 2-substituted pyridine type compounds, bialicyclic tertiary amines have been measured as a function of the nature of the solvent. In the case of cyclic aliphatic amines, like piperidine, morpholine, piperazine, thiomorpholine, the nitrogen is more shielded in concentrated solution compared to that in dilute solution whereas in the hydrogen bonding and protonating solvents there is a prominent deshielding. 2-Substituted pyridines studied can be further divided into four sub groups. The site of hydrogen bonding and protonation in 2-amino, 2-hydroxy and 2-mercapto pyridines have been conclusively proved from the 15N-NMR chemical shifts and the well-known tautomeric forms of the above compounds. Similarly in the case of 2-(2-thienyl)pyridine and 2-(3-thienyl)pyridine, the site of donation has been proved as the nitrogen of the pyridine ring in both the compounds. In a similar manner, the site of hydrogen bonding and protonation in two individual compounds 2-anilinopyridine and 2-(2-pyridyl)benzimidazole have also been established. Among the bialicyclic amines, 1,2-diazabicyclo[2.2.2]octane (DABCO) behaved differently from the other two compounds. In both 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), it was possible to show that N 1-nitrogen in both the compounds is the site of donation. The effect of the second donor site on the 15N-NMR chemical shift, the site of donation in the selected compounds and some typical compounds reported in literature have been presented and discussed.

Someswara Rao, N.; Babu Rao, G.; Murthy, B. N.; Das, M. Maria; Prabhakar, T.; Lalitha, M.

2002-10-01

38

Long-term 15N tracking from biological N fixation across different plant and humus components of the boreal forest  

NASA Astrophysics Data System (ADS)

Biological N2 fixation by cyanobacteria associated with feather mosses is an important cog in the nitrogen (N) cycle of boreal forests; still, our understanding of the turnover and fate of N fixed by this association remains greatly incomplete. The 15N signature of plants and soil serves as a powerful tool to explore N dynamics in forest ecosystems. In particular, in the present study we aimed to investigate the contribution of N2 fixation to ?15N signatures of plants and humus component of the boreal forest. Here we present results from a long-term (7 years) tacking of labelled 15N2 across the humus layer, seedlings of the tree species Pinus sylvestris, two common dwarf shrub species (Empetrum hermaphroditum and Vaccinium vitis-idaea) and the feather moss Pleurozium schreibery. The enriched experiment was conducted in 2005 in a natural boreal forest in northern Sweden. Two different treatments (10% 15N2 headspace enrichment and control) were setup in nine different plots (0.5 x 0.5 m) within the forest. We observed a significant reduction of ?15N signature of the 15N-enriched moss that could be explained by a growth dilution effect. Nevertheless, after 5 years since 15N2 enrichment some of the label 15N was still detected on the moss and in particular in the dead tissue. We could not detect a clear transfer of the labelled 15N2 from the moss-cyanobacteria system to other components of the ecosystem. However, we found consistence relationship through time between increments of ?15N signature of some of the forest components in plots which exhibited higher N fixation rates in the moss. In particular, changes in natural abundance ?15N that could be associated with N fixation were more apparent in the humus layer, the dwarf shrub Vaccinium vitis-idaea and the pine seedlings when comparing across plots and years.

Arroniz-Crespo, Maria; Jones, David L.; Zackrisson, Olle; Nilsson, Marie-Charlotte; DeLuca, Thomas H.

2014-05-01

39

Natural abundance 17O NMR study of ?-substituted methyl acetates  

NASA Astrophysics Data System (ADS)

Natural abundance 17O NMR chemical shift data for 10 substituted methyl acetates and 7 analogs, recorded in acetonitrile at 75°C, are reported. Variation in the carbonyl and single-bond oxygen signal are observed for formal ?-substitution and do not correlate with inductive effects. The data appear to be consistent with ? effects for analogous systems.

Boykin, D. W.; Subramanian, T. S.; Baumstark, A. L.

1989-01-01

40

1H, 13C and 15N NMR assignments of the E. coli peptide deformylase in complex with a natural inhibitor called actinonin.  

PubMed

In eubacteria, the formyl group of nascent polypeptides is removed by peptide deformylase protein (PDF). This is the reason why PDF has received special attention in the course of the search for new antibacterial agents. We observed by NMR that actinonin, a natural inhibitor, induced drastic changes in the HSQC spectrum of E. coli PDF. We report here the complete NMR chemical shift assignments of PDF resonances bound to actinonin. PMID:19636969

Larue, Valéry; Seijo, Bili; Tisne, Carine; Dardel, Frédéric

2009-06-01

41

Stable isotopes (?13C and ?15N) of organic matrix from coral skeleton  

PubMed Central

The evolutionary success of reef-building corals in nutrient-poor tropical waters is attributed to endosymbiotic dinoflagellates. The algae release photosynthetic products to the coral animal cells, augment nutrient flux, and enhance the rate of coral calcification. Natural abundance of stable isotopes (?13C and ?18O) provides answers to modern and paleobiological questions about the effect of photosymbiosis on sources of carbon and oxygen in coral skeletal calcium carbonate. Here we compare 17 species of symbiotic and nonsymbiotic corals to determine whether evidence for photosymbiosis appears in stable isotopes (?13C and ?15N) of an organic skeletal compartment, the coral skeletal organic matrix (OM). Mean OM ?13C in symbiotic and nonsymbiotic corals was similar (-26.08‰ vs. -24.31‰), but mean OM ?15N was significantly depleted in 15N in the former (4.09‰) relative to the latter (12.28‰), indicating an effect of the algae on OM synthesis and revealing OM ?15N as a proxy for photosymbiosis. To answer an important paleobiological question about the origin of photosymbiosis in reef-building corals, we applied this proxy test to a fossil coral (Pachythecalis major) from the Triassic (240 million years ago) in which OM is preserved. Mean OM ?15N was 4.66‰, suggesting that P. major was photosymbiotic. The results show that symbiotic algae augment coral calcification by contributing to the synthesis of skeletal OM and that they may have done so as early as the Triassic.

Muscatine, Leonard; Goiran, Claire; Land, Lynton; Jaubert, Jean; Cuif, Jean-Pierre; Allemand, Denis

2005-01-01

42

Juniperus communis L. ssp. communis at Balnaguard, Scotland: Foliar carbon discrimination (?C) and 15-N natural abundance (?N) suggest gender-linked differences in water and N use  

Microsoft Academic Search

The ecophysiology of stands of Juniperus communis L. ssp. communis at Balnaguard was examined by the relatively non-invasive methods of analysis of foliar · C and ·N and the N and chlorophyll contents of foliar samples of genets of known sex and location in three sub-sites. The ratio of male to female plants was close to 1.0 on the two

Paul W. Hill; L. L. Handley; J. A. Raven

1996-01-01

43

Complete Thermodynamic Characterization of the Multiple Protonation Equilibria of the Aminoglycoside Antibiotic Paromomycin: A Calorimetric and Natural Abundance 15N NMR Study  

Microsoft Academic Search

The binding of aminoglycoside antibiotics to a broad range of macromolecular targets is coupled to protonation of one or more of the amino groups that typify this class of drugs. Determining how and to what extent this linkage influences the energetics of the aminoglycoside-macromolecule binding reaction requires a detailed understanding of the thermodynamics associated with the protonation equilibria of the

Christopher M. Barbieri; Daniel S. Pilch

2006-01-01

44

Chlorine-36 abundance in natural and synthetic perchlorate  

SciTech Connect

Perchlorate (ClO{sub 4}{sup -}) is ubiquitous in the environment. It occurs naturally as a product of atmospheric photochemical reactions, and is synthesized for military, aerospace, and industrial applications. Nitrate-enriched soils of the Atacama Desert (Chile) contain high concentrations of natural ClO{sub 4}{sup -}; nitrate produced from these soils has been exported worldwide since the mid-1800's for use in agriculture. The widespread introduction of synthetic and agricultural ClO{sub 4}{sup -} into the environment has complicated attempts to understand the geochemical cycle of ClO{sub 4}{sup -}. Natural ClO{sub 4}{sup -} samples from the southwestern United States have relatively high {sup 36}Cl abundances ({sup 36}Cl/Cl = 3,100 x 10{sup -15} to 28,800 x 10{sup -15}), compared with samples of synthetic ({sup 36}Cl/Cl = 0.0 x 10{sup -15} to 40 x 10{sup -15}) and Atacama Desert ({sup 36}Cl/Cl = 0.9 x 10{sup -15} to 590 x 10{sup -15}) ClO{sub 4}{sup -}. These data give a lower limit for the initial {sup 36}Cl abundance of natural ClO{sub 4}{sup -} and provide temporal and other constraints on its geochemical cycle.

Heikoop, Jeffrey M [Los Alamos National Laboratory; Dale, M [NON LANL; Sturchio, Neil C [UNIV OF ILLIONOIS; Caffee, M [PURDUE UNIV; Belosa, A D [UNIV OF ILLINOIS; Heraty, Jr., L J [UNIV OF ILLINOIS; Bohike, J K [RESTON, VA; Hatzinger, P B [SHAW ENIVIORNMENTAL C0.; Jackson, W A [TEXAS TECH; Gu, B [ORNL

2009-01-01

45

Mycorrhizal Fungi Provide Most of the Nitrogen for Symbiotic Arctic Plants: 15N Evidence  

NASA Astrophysics Data System (ADS)

When soil nitrogen is in short supply, most terrestrial plants form symbioses with fungi (mycorrhizae) in which fine hyphal threads take up soil nitrogen, transport it into plant roots, and in return receive plant sugars. Because the transfer rates are very difficult to measure in nature, ecologists need new tools by which to assess the role of mycorrhizal fungi in carbon and nitrogen cycling. Recent studies indicate that the natural abundance of 15N taken up from the soil by hyphae is changed during transfer of nitrogen to roots; the result is large differences among the natural abundance of 15N in soil, symbiotic plants, and symbiotic fungi that depend on the mass balance of nitrogen in the mycorrhizal symbiosis. Measurements were carried out in acidic tussock tundra at the Toolik Lake LTER site in Arctic Alaska (68\\deg N 149\\deg W). The \\delta15N of soil N was 1.5%, of soil ammonium was 1.5%, of ericoid and ectomycorrhizal plants was -5.0%, and of ectomycorrhizal fungi was 7.0 parts per mille%. The mass balance of the 15N shows that the plants received 61-86% of their nitrogen from the fungal hyphae. These values, when combined with known plant growth rates, reveal that the plants provided 7-16% of their photosynthetic carbon to the fungi for growth and respiration, or about 25% of all carbon allocated to belowground processes. This analytical technique could be readily applied to other nitrogen-limited ecosystems such as many temperate and boreal forests to quantify the importance for terrestrial carbon and nitrogen cycling of mycorrhizally mediated transfers at the plant-soil interface.

Hobbie, J. E.; Hobbie, E. A.

2004-12-01

46

N-15 NMR spectra of naturally abundant nitrogen in soil and aquatic natural organic matter samples of the International Humic Substances Society  

USGS Publications Warehouse

The naturally abundant nitrogen in soil and aquatic NOM samples from the International Humic Substances Society has been characterized by solid state CP/MAS 15N NMR. Soil samples include humic and fulvic acids from the Elliot soil, Minnesota Waskish peat and Florida Pahokee peat, as well as the Summit Hill soil humic acid and the Leonardite humic acid. Aquatic samples include Suwannee River humic, fulvic and reverse osmosis isolates, Nordic humic and fulvic acids and Pony Lake fulvic acid. Additionally, Nordic and Suwannee River XAD-4 acids and Suwannee River hydrophobic neutral fractions were analyzed. Similar to literature reports, amide/aminoquinone nitrogens comprised the major peaks in the solid state spectra of the soil humic and fulvic acids, along with heterocyclic and amino sugar/terminal amino acid nitrogens. Spectra of aquatic samples, including the XAD-4 acids, contain resolved heterocyclic nitrogen peaks in addition to the amide nitrogens. The spectrum of the nitrogen enriched, microbially derived Pony Lake, Antarctica fulvic acid, appeared to contain resonances in the region of pyrazine, imine and/or pyridine nitrogens, which have not been observed previously in soil or aquatic humic substances by 15N NMR. Liquid state 15N NMR experiments were also recorded on the Elliot soil humic acid and Pony Lake fulvic acid, both to examine the feasibility of the techniques, and to determine whether improvements in resolution over the solid state could be realized. For both samples, polarization transfer (DEPT) and indirect detection (1H-15N gHSQC) spectra revealed greater resolution among nitrogens directly bonded to protons. The amide/aminoquinone nitrogens could also be observed by direct detection experiments.

Thorn, K. A.; Cox, L. G.

2009-01-01

47

Fast NMR data acquisition from bicelles containing a membrane-associated peptide at natural-abundance.  

PubMed

In spite of recent technological advances in NMR spectroscopy, its low sensitivity continues to be a major limitation particularly for the structural studies of membrane proteins. The need for a large quantity of a membrane protein and acquisition of NMR data for a long duration are not desirable. Therefore, there is considerable interest in the development of methods to speed up the NMR data acquisition from model membrane samples. In this study, we demonstrate the feasibility of acquiring two-dimensional spectra of an antimicrobial peptide (MSI-78; also known as pexiganan) embedded in isotropic bicelles using natural-abundance (15)N nuclei. A copper-chelated lipid embedded in bicelles is used to speed-up the spin-lattice relaxation of protons without affecting the spectral resolution and thus enabling fast data acquisition. Our results suggest that even a 2D SOFAST-HMQC spectrum can be obtained four times faster using a very small amount (?3 mM) of a copper-chelated lipid. These results demonstrate that this approach will be useful in the structural studies of membrane-associated peptides and proteins without the need for isotopic enrichment for solution NMR studies. PMID:21939237

Yamamoto, Kazutoshi; Vivekanandan, Subramanian; Ramamoorthy, Ayyalusamy

2011-11-01

48

Fast NMR Data Acquisition From Bicelles Containing a Membrane-Associated Peptide at Natural-Abundance  

PubMed Central

In spite of recent technological advances in NMR spectroscopy, its low sensitivity continues to be a major limitation particularly for the structural studies of membrane proteins. The need for a large quantity of a membrane protein and acquisition of NMR data for a long duration are not desirable. Therefore, there is considerable interest in the development of methods to speed up the NMR data acquisition from model membrane samples. In this study, we demonstrate the feasibility of acquiring two-dimensional spectra of an antimicrobial peptide (MSI-78; also known as pexiganan) embedded in isotropic bicelles using natural-abundance 15N nuclei. A copper-chelated lipid embedded in bicelles is used to speed-up the spin-lattice relaxation of protons without affecting the spectral resolution and thus enabling fast data acquisition. Our results suggest that even a 2D SOFAST-HMQC spectrum can be obtained four times faster using a very small amount (~3 mM) of a copper-chelated lipid. These results demonstrate that this approach will be useful in the structural studies of membrane-associated peptides and proteins without the need for isotopic enrichment for solution NMR studies.

Yamamoto, Kazutoshi; Vivekanandan, Subramanian; Ramamoorthy, Ayyalusamy

2011-01-01

49

Rapid heteronuclear single quantum correlation NMR spectra at natural abundance.  

PubMed

A novel NMR experiment, the so-called ASAP-HSQC, is introduced that allows the detection of heteronuclear one-bond correlations in less than 30 s on small molecules at natural abundance without compromises in sweep width, resolution or spectral quality. Equally, the experiment allows a significant increase in digital resolution or a moderate senstitivity enhancement in the same overall experiment time compared to a conventional HSQC. The gain is a consequence of keeping all unused proton magnetization along z during acquisition, so that the previously reported ASAP and ALSOFAST approaches can be transferred from HMQC to HSQC-type experiments. Next to basic and broadband pulse sequences, a characterization of the sequence with respect to minimum measurement time, sensitivity gain, and advantages in resolution compared to state-of-the-art experiments is given. PMID:24417402

Schulze-Sünninghausen, David; Becker, Johanna; Luy, Burkhard

2014-01-29

50

C15N in Diffuse Molecular Clouds  

NASA Astrophysics Data System (ADS)

We report the first detection of C15N in absorption in diffuse molecular gas from a detailed examination of archival VLT/UVES data covering the CN lines near 3875 Å. Absorption from the C15N isotopologue is detected in three out of the four directions studied and appears as a very weak feature between the main 12CN and 13CN absorption lines. Column densities for each CN isotopologue are determined through profile fitting, after accounting for weak additional line-of-sight components, which are observed in CH and CH+. The weighted mean value of C14N/C15N for the three sight lines with detections of C15N is 277±16, in very good agreement with the terrestrial 14N/15N ratio of 272. Our results help to clarify the situation regarding the nitrogen isotope ratio in the solar neighborhood, with important implications for interstellar chemistry and Galactic chemical evolution.

Federman, Steven Robert; Ritchey, Adam M.; Lambert, David L.

2014-06-01

51

Diversity and abundance of phosphonate biosynthetic genes in nature  

PubMed Central

Phosphonates, molecules containing direct carbon–phosphorus bonds, compose a structurally diverse class of natural products with interesting and useful biological properties. Although their synthesis in protozoa was discovered more than 50 y ago, the extent and diversity of phosphonate production in nature remains poorly characterized. The rearrangement of phosphoenolpyruvate (PEP) to phosphonopyruvate, catalyzed by the enzyme PEP mutase (PepM), is shared by the vast majority of known phosphonate biosynthetic pathways. Thus, the pepM gene can be used as a molecular marker to examine the occurrence and abundance of phosphonate-producing organisms. Based on the presence of this gene, phosphonate biosynthesis is common in microbes, with ?5% of sequenced bacterial genomes and 7% of genome equivalents in metagenomic datasets carrying pepM homologs. Similarly, we detected the pepM gene in ?5% of random actinomycete isolates. The pepM-containing gene neighborhoods from 25 of these isolates were cloned, sequenced, and compared with those found in sequenced genomes. PEP mutase sequence conservation is strongly correlated with conservation of other nearby genes, suggesting that the diversity of phosphonate biosynthetic pathways can be predicted by examining PEP mutase diversity. We used this approach to estimate the range of phosphonate biosynthetic pathways in nature, revealing dozens of discrete groups in pepM amplicons from local soils, whereas hundreds were observed in metagenomic datasets. Collectively, our analyses show that phosphonate biosynthesis is both diverse and relatively common in nature, suggesting that the role of phosphonate molecules in the biosphere may be more important than is often recognized.

Yu, Xiaomin; Doroghazi, James R.; Janga, Sarath C.; Zhang, Jun Kai; Circello, Benjamin; Griffin, Benjamin M.; Labeda, David P.; Metcalf, William W.

2013-01-01

52

PARTITIONING THE RELATIVE INFLUENCE OF SOIL N, MYCORRHIZAE, AND FOLIAR N UPTAKE ON FOLIAR delta15N PATTERNS: CAN WE DETECT FOLIAR UPTAKE OF REACTIVE N?  

Microsoft Academic Search

Vegetation is an important sink for atmospheric reactive N in N-limited systems and may be capable of incorporating reactive N compounds directly into leaves through the foliar uptake pathway. A proxy for atmospheric reactive N entering vegetation would be useful to estimate the impact of direct foliar N uptake on plant metabolism. Natural abundance foliar N isotopic composition (delta15N) is

D. Vallano; J. P. Sparks

2009-01-01

53

THE EFFECTS OF PARAMAGNETIC RELAXATION REAGENTS ON 15N SPIN RELAXATION AND THE USE OF GD(DPM)3 AS A NITROGEN-15 NUCLEAR MAGNETIC RESONANCE SPIN LABEL  

EPA Science Inventory

Electron-nuclear relaxation times (T(1) sup e's) for (15)N and (13)C in natural abundance are measured for a series of amines of a wide range of pK(a)s using four paramagnetic relaxation reagents that are soluable in organic solutions. Cr(acac)3 and Cr(dpm)3 are seen to affect th...

54

(15)N-(15)N proton assisted recoupling in magic angle spinning NMR.  

PubMed

We describe a new magic angle spinning (MAS) NMR experiment for obtaining (15)N-(15)N correlation spectra. The approach yields direct information about the secondary and tertiary structure of proteins, including identification of alpha-helical stretches and interstrand connectivity in antiparallel beta-sheets, which are of major interest for structural studies of membrane proteins and amyloid fibrils. The method, (15)N-(15)N proton assisted recoupling (PAR), relies on a second-order mechanism, third spin assisted recoupling (TSAR), used previously in the context of (15)N-(13)C and (13)C-(13)C polarization transfer schemes. In comparison to (15)N-(15)N proton-driven spin diffusion experiments, the PAR technique accelerates polarization transfer between (15)N's by a factor of approximately 10(2)-10(3) and is furthermore applicable over the entire range of currently available MAS frequencies (10-70 kHz). PMID:19334788

Lewandowski, Józef R; De Paëpe, Gaël; Eddy, Matthew T; Griffin, Robert G

2009-04-29

55

Analytical methods in 15 N research  

Microsoft Academic Search

Although the stable isotope15N is an indispensable tool in research to trace the fate of fertilizer nitrogen in soil\\/plant systems, the analytical methods used in this research are time consuming and prone to many errors. This paper outlines the methods used in an international program of nitrogen research coordinated by the International Fertilizer Development Center (IFDC). The different steps in

RJ Buresh; ER Austin; ET Craswell

1982-01-01

56

?15N as a Potential Paleoenvironmental Proxy for Nitrogen Loading in Chesapeake Bay  

NASA Astrophysics Data System (ADS)

Stable isotope analysis of Eastern Oyster (Crassostrea virginica) and other mollusk shells from archaeological sites is a useful means of acquiring paleoenvironmental data. Recently, nitrogen isotopes have been identified as a potential new proxy in these shells. ?15N content in mollusk shells is affected by numerous anthropogenic and natural influences and may be used as an environmental proxy for nitrogen loading conditions. Chesapeake Bay is well known for both historic and modern pollution problems from numerous anthropogenic sources, such as fertilizer runoff, sewage discharge, and densely populated land use and serves as an ideal study location for long-term nitrogen loading processes. Longer records of these processes may be recorded in abundant archaeological remains around the bay, however, little is known about the stability of ?15N and %N in shell material over recent geologic time. In this study, 90 archaeological C. virginica shells were collected by the Smithsonian Institution from the Rhode River Estuary within Chesapeake Bay and range in age from ~150 to 3200 years old. Twenty-two modern C. virginica shells were also collected from nearby beds in the bay. All shell samples were subsampled from the resilifer region of the calcitic shell using a hand-held micro drill and were analyzed using EA-IRMS analysis to determine the potential temporal variability of ?15N and %N as well as creating a baseline for ancient nitrogen conditions in the bay area. Modern POM water samples and C. virginica soft tissues were also analyzed in this study to determine the degree of seasonal variation of ?15N and %N in Chesapeake Bay.

Black, H. D.; Andrus, C. F.; Rick, T.; Hines, A.

2013-12-01

57

The Rare Isotopomers of HCN: HC15N and DC15N. Rotational Spectrum and Resolved Nuclear Hyperfine Structures due to 15N and D  

Microsoft Academic Search

In the present work the J+1<--J rotational transitions, with J=0-7, of HC15N and the J+1<--J rotational transitions, with J=0-7, 9, of DC15N have been investigated. The Lamb-dip technique has been employed in order to resolve the hyperfine structure due to deuterium and 15N. For HC15N, the hyperfine parameters have been determined for the first time. With respect to DC15N, only

Gabriele Cazzoli; Cristina Puzzarini; Jürgen Gauss

2005-01-01

58

15N magnetic resonance hyperpolarization via the reaction of parahydrogen with 15N-propargylcholine.  

PubMed

(15)N-Propargylcholine has been synthesized and hydrogenated with para-H(2). Through the application of a field cycling procedure, parahydrogen spin order is transferred to the (15)N resonance. Among the different isomers formed upon hydrogenation of (15)N-propargylcholine, only the nontransposed derivative contributes to the observed N-15 enhanced emission signal. The parahydrogen-induced polarization factor is about 3000. The precise identification of the isomer responsible for the observed (15)N enhancement has been attained through a retro-INEPT ((15)N-(1)H) experiment. T(1) of the hyperpolarized (15)N resonance has been estimated to be ca. 150 s, i.e., similar to that reported for the parent propargylcholine (144 s). Experimental results are accompanied by theoretical calculations that stress the role of scalar coupling constants (J(HN) and J(HH)) and of the field dependence in the formation of the observed (15)N polarized signal. Insights into the good cellular uptake of the compound have been gained. PMID:22663300

Reineri, Francesca; Viale, Alessandra; Ellena, Silvano; Alberti, Diego; Boi, Tommaso; Giovenzana, Giovanni Battista; Gobetto, Roberto; Premkumar, Samuel S D; Aime, Silvio

2012-07-11

59

15N-depleted N2O as a product of nitrification  

Microsoft Academic Search

Recent interest in the role of nitrous oxide in the natural nitrogen cycle has focused on its production through the nitrification process1. Nitrous oxide depleted in 15N has been found in the shallow water column of the eastern tropical Pacific Ocean2, suggesting that 15N is depleted during N2O production. Here we report significant 15N depletion in N2O produced by bacterial

Naohiro Yoshida

1988-01-01

60

A 115-year ?15N record of cumulative nitrogen pollution in California serpentine grasslands  

NASA Astrophysics Data System (ADS)

Until the 1980s, California’s biodiverse serpentine grasslands were threatened primarily by development and protected by reserve creation. However, nitrogen (N) fertilization due to increasing fossil fuel emissions in the expanding Bay Area is thought to be contributing to rapid, recent invasion of these ecosystems by exotic annual grasses that are displacing rare and endemic serpentine species. Documenting the cumulative effects of N deposition in this ecosystem can direct policy and management actions to mitigate the role of N deposition in its transformation. Natural abundance stable isotopes of N in vegetation have been increasingly used as bio-indicators of N deposition patterns and subsequent changes to plant N cycling and assimilation. However, the long-term record of atmospheric reactive N enrichment and the resulting changes in ecosystem N dynamics have yet to be adequately reconstructed in many ecosystems. Museum archives of vascular plant tissue are valuable sources of materials to reconstruct temporal and spatial isotopic patterns of N inputs to ecosystems. Here, we present N stable isotope data from archived and current specimens of an endemic California serpentine grassland species, leather oak (Quercus durata), since 1895 across the greater San Francisco Bay region. We measured spatial and temporal trends in stable isotope composition (?15N and ?13C) and concentration (%N and %C) of historical and current samples of leather oak leaves from sites within the Bay Area, impacted by increasing development, and sites northeast of the Bay Area, with significantly lower rates of urbanization and industrialization. Specifically, we sampled dry museum and fresh leaf specimens from serpentine sites within Lake (n=27) and Santa Clara (n=30) counties dating from 1895 to 2010. Leaf ?15N values were stable from 1895 to the 1950s and then decreased strongly throughout the last 50 years as fossil fuel emissions rapidly increased in the Bay Area, indicating that N pollution is being retained in serpentine grassland ecosystems. Leaf ?15N values in the high-deposition region declined at a rate of -0.041‰ yr-1, while leaf ?15N values in the low-deposition region did not show a strong pattern. In both regions, leaf ?13C values declined through time as atmospheric CO2 concentrations increased in response to fossil fuel combustion (the Suess effect). Leaf %N and %C values did not present any clear patterns at sites within or outside of the Bay Area. We conclude that using natural abundance stable isotope values in leaves can indicate variation in N pollution inputs across wide spatial and temporal scales and that archived plant samples can provide valuable baselines against which to assess changes in regional N cycling and subsequent ecological impacts on vegetation.

Vallano, D.; Zavaleta, E. S.

2010-12-01

61

Correlation between modern plant ? 15N values and activity areas of Medieval Norse farms  

Microsoft Academic Search

This further nitrogen isotopic study of Greenlandic Norse archaeological sites provides new evidence of the affect of past human activity on modern plant ?15N values. Grass samples were taken from a number of spatially defined features at four Norse farms and one site interpreted to be a seasonally occupied herding station (sæter). At the farms, un-naturally high ?15N values were

R. G. Commisso; D. E. Nelson

2008-01-01

62

Modeling amino acid side chains in proteins: 15N NMR spectra of guanidino groups in nonpolar environments.  

PubMed

Natural-abundance 15N NMR spectroscopy on dodecylguanidine reveals solvent and protonation effects that model those that could occur for the arginine side chain in proteins. Our results demonstrate that the 15N chemical shifts of the terminal guanine nitrogens strongly depend on the solvent chosen for measurements. A polar H-bond-donating solvent like water has strongly deshielding effects on the neutral guanidine group (with the latter acting predominantly as an H-bond acceptor). As a result, a substantial upfield shift occurs when neutral guanidine is dissolved instead in a non-H-bonding solvent (chloroform). These solvent effects can be as large as those induced by protonation changes. This limits the ability of 15N chemical shifts to distinguish the protonation state of the arginine side chain, at least without specific knowledge of its environment. These results help to reconcile previous interpretations about the protonation state arg-82 in the M state of bacteriorhodopsin based on FTIR and 15N NMR spectroscopy. That is, contrary to earlier conclusions from solid-state NMR, the side chain of arg-82 could undergo a deprotonation between the bR and M states, but only if it also experienced a significant decrease in the H-bonding character and polarity of its environment. In fact, the average 15N chemical shift of the two Neta of arg-82 in bacteriorhodopsin's M intermediate (from the previous NMR measurements) is 17 ppm upfield from the corresponding value for the deprotonated arginine side chain in aqueous solution at pH >14, but only 3 ppm upfield from the value for deprotonated dodecylguanidine in chloroform. PMID:16853157

Xiao, Yaowu; Braiman, Mark

2005-09-01

63

Diversity, abundance and natural products of marine sponge-associated actinomycetes.  

PubMed

Actinomycetes are known for their unprecedented ability to produce novel lead compounds of clinical and pharmaceutical importance. This review focuses on the diversity, abundance and methodological approaches targeting marine sponge-associated actinomycetes. Additionally, novel qPCR data on actinomycete abundances in different sponge species and other environmental sources are presented. The natural products literature is covered, and we are here reporting on their chemical structures, their biological activities, as well as the source organisms from which they were isolated. PMID:24496105

Abdelmohsen, Usama Ramadan; Bayer, Kristina; Hentschel, Ute

2014-03-01

64

Plantation vs. natural forest: Matrix quality determines pollinator abundance in crop fields  

PubMed Central

In terrestrial ecosystems, ecological processes and patterns within focal patches frequently depend on their matrix. Crop fields (focal patches) are often surrounded by a mosaic of other land-use types (matrix), which may act as habitats for organisms and differ in terms of the immigration activities of organisms to the fields. We examined whether matrix quality affects wild pollinator abundance in crop fields, given that the species (Apis cerana) generally nest in the cavities of natural trees. We examined fields of a pollination-dependent crop surrounded by plantations and natural forests, which comprised the matrix. Our analysis revealed a clear positive effect of the natural forest on the pollinator abundance, but the plantation forest had little effects. These indicate that agricultural patches are influenced by their matrix quality and the resulting crop pollinator abundance, suggesting the importance of matrix management initiatives such as forest restoration surrounding agricultural fields to improve crop production.

Taki, Hisatomo; Yamaura, Yuichi; Okabe, Kimiko; Maeto, Kaoru

2011-01-01

65

Fate and metabolism of [15N]2,4,6-trinitrotoluene in soil.  

PubMed

The fates of the labels from [14C] and [15N] trinitrotoluene were analyzed in bioreactors under aerobic conditions in soil treated by a fungal bioremediation process with Stropharia rugosoannulata and in control soil. Up to 17.5% of the 15N label had a different fate than the 14C label. Three N-mineralization processes were identified in detailed experiments with [15N]TNT. About 2% of the 15N label was found as NO3- and NH4+, showing simultaneous processes of direct TNT denitration (I) and reduction with cleavage of the amino groups (II). The enrichment of NO2-/NO3- (up to 7.5 atom% 15N abundance) indicates the formation of Meisenheimer complexes with a denitration of [15N]TNT. A 1.4% of the label was found distributed between N2O and N2. However, the 15N enrichment of the N2O (up to 38 atom%) demonstrated that both N atoms were generated from the labeled TNT and clearly indicates a novel formation process (III). We propose, as an explanation, the generation of N2O by cleavage from condensed azoxy metabolites. In addition, 1.7% of the 15N label was detected as biogenic amino acids in the wheat straw containing the fungus. Overall, 60 to 85% of the applied [15N]TNT was degraded and 52 to 64% was found as nonextractable residues in the soil matrix. Three percent was detected as 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene. PMID:15352472

Weiss, Martin; Geyer, Roland; Russow, Rolf; Richnow, Hans H; Kästner, Matthias

2004-08-01

66

Review: Biocatalytic transformations of ferulic acid: An abundant aromatic natural product  

Microsoft Academic Search

In this review we examine the fascinating array of microbial and enzymatic transformations of ferulic acid. Ferulic acid is an extremely abundant, preformed phenolic aromatic chemical found widely in nature. Ferulic acid is viewed as a commodity scale, renewable chemical feedstock for biocatalytic conversion to other useful aromatic chemicals. Most attention is focused on bioconversions of ferulic acid itself. Topics

J P N Rosazza; Z Huang; L Dostal; T Volm; B Rousseau

1995-01-01

67

Microscopic nature of 0{sup +} states populated in large abundance in deformed nuclei  

SciTech Connect

The low-lying excited 0{sup +} states populated in large abundance in several deformed nuclei through two-nucleon transfer reaction experiments are thoroughly investigated within a microscopic multiphonon framework. The approach reproduces satisfactorily the experimental data and provides exhaustive information about the nature of those states.

Lo Iudice, N. [Dipartimento di Scienze Fisiche, Universita di Napoli 'Federico II' and Istituto Nazionale di Fisica Nucleare, Monte S Angelo, Via Cintia I-80126 Napoli (Italy); Sushkov, A. V.; Shirikov, N. Yu. [Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna (Russian Federation)

2008-05-12

68

New insights into the structure and chemistry of Titan's tholins via13C and 15N solid state nuclear magnetic resonance spectroscopy  

NASA Astrophysics Data System (ADS)

Tholins are complex C,N-containing organic compounds produced in the laboratory. They are considered to provide materials that are analogous to those responsible for the haze observed in Titan's atmosphere. These compounds present an astrobiological interest due to their ability to release amino acids upon hydrolysis. Their chemical structure has been investigated using a large number of techniques. However, to date no detailed nuclear magnetic resonance (NMR) study has been performed on these materials despite the high potential of this technique for investigating the environment of given nuclei. Here 13C and 15N solid state NMR spectroscopy was applied to obtain new insights into the chemical structure of tholins produced through plasma discharge in gaseous N2sbnd CH4 mixtures designed to simulate the atmosphere of Titan. Due to the low natural abundance of these isotopes, a 13C and 15N-enriched tholin sample was synthesized using isotopically enriched gas precursors. Various pulse sequences including 13C and 15N single pulse, 1Hsbnd 13C and 1Hsbnd 15N cross-polarisation and 1Hsbnd 15Nsbnd 13C double cross-polarisation were used. These techniques allowed complete characterisation of the chemical and structural environments of the carbon and nitrogen atoms. The NMR assignments were supplemented and confirmed by ab initio electronic structure calculations for model structures and molecular fragments.

Derenne, S.; Coelho, C.; Anquetil, C.; Szopa, C.; Rahman, A. S.; McMillan, P. F.; Corà, F.; Pickard, C. J.; Quirico, E.; Bonhomme, C.

2012-11-01

69

Natural abundance high-resolution solid state 2 H NMR spectroscopy  

NASA Astrophysics Data System (ADS)

We report for the first time an approach for natural abundance solid state 2H NMR spectroscopy involving magic angle sample spinning (MAS), high-power 1H decoupling (HPPD) and 1H- 2H cross polarization (CP). Taking tetrakis(trimethylsilyl)silane (TTMSS), adamantane, 1-chloroadamantane, hexamethylbenzene (HMB), 2,2-dimethyl-1,3-propanediol (DMPD) and 2-hydroxymethyl-2-methyl-1,3-propanediol (HMPD) as examples, it has been shown that the combination of HPPD and MAS can be applied readily to study rotator phase solids, allowing isotropic peaks arising from chemically inequivalent 2H nuclei to be resolved. For natural abundance samples of TTMSS and chloroadamantane, it has been shown that 2H CP/HPPD/MAS NMR experiments, involving polarization transfer from 1H to 2H, may provide considerable sensitivity enhancement in comparison with single pulse experiments.

Aliev, Abil E.; Harris, Kenneth D. M.; Apperley, David C.

1994-08-01

70

Natural abundance high-resolution solid state 2 H NMR spectroscopy  

NASA Astrophysics Data System (ADS)

We report for the first time an approach for natural abundance solid state 2 H NMR spectroscopy involving magic angle sample spinning (MAS), high-power 1 H decoupling (HPPD) and 1 H- 2 H cross polarization (CP). Taking tetrakis(trimethylsilyl)silane (TTMSS), adamantane, 1-chloroadamantane, hexamethylbenzene (HMB), 2,2-dimethyl-1,3-propanediol (DMPD) and 2-hydroxymethyl-2-methyl-1,3-propanediol (HMPD) as examples, it has been shown that the combination of HPPD and MAS can be applied readily to study rotator phase solids, allowing isotropic peaks arising from chemically inequivalent 2 H nuclei to be resolved. For natural abundance samples of TTMSS and chloroadamantane, it has been shown that 2 H CP/HPPD/MAS NMR experiments, involving polarization transfer from 1 H to 2 H, may provide considerable sensitivity enhancement in comparison with single pulse experiments.

Aliev, Abil E.; Harris, Kenneth D. M.; Apperley, David C.

1994-08-01

71

Enantiomeric analysis using natural abundance deuterium 3D NMR spectroscopy in polypeptide chiral oriented media  

NASA Astrophysics Data System (ADS)

The use of natural abundance deuterium (NAD) three-dimensional (3D) NMR experiment in chiral liquid crystals (CLC) is reported and discussed. This homonuclear autocorrelation 3D experiment allows assigning deuterium signals of weakly aligned molecules at natural isotopic abundance. It provides an efficient strategy for identifying the spectral enantio-discriminations on NAD spectra. We demonstrate that NAD 3D NMR is feasible within reasonable experimental times (14 h) using the 3D Quadrupole Double-Quantum NMR sequence [O. Lafon, P. Lesot, Chem. Phys. Lett. 404 (2005) 90] and a 14.1 T NMR spectrometer equipped with a selective 5 mm deuterium NMR cryoprobe. The analytical potentialities of this technique are illustrated in the case of (±)-but-2-yn-1-ol dissolved in poly-?-benzyl- L-glutamate/CHCl 3 mesophase.

Lesot, Philippe; Lafon, Olivier

2008-06-01

72

Nitrogen fixation in legumes and actinorhizal plants in natural ecosystems: values obtained using N natural abundance  

Microsoft Academic Search

Background: Nitrogen fixation has been quantified for a range of crop legumes and actinorhizal plants under different agricultural\\/?agroforestry conditions but much less is known of legume and actinorhizal plant N2 fixation in natural ecosystems.Aims: To assess the proportion of total plant N derived from the atmosphere via the process of N2 fixation (%Ndfa) by actinorhizal and legume plants in natural

Mitchell Andrews; Euan K. James; Janet I. Sprent; Robert M. Boddey; Eduardo Gross; Fabio Bueno dos Reis Jr

2011-01-01

73

Natural abundance 2H-ERETIC-NMR authentication of the origin of methyl salicylate.  

PubMed

Methyl salicylate is a compound currently used in the creation of many flavors. It can be obtained by synthesis or from two natural sources: essential oil of wintergreen and essential oil of sweet birch bark. Deuterium site-specific natural isotope abundance (A(i)) determination by NMR spectroscopy with the method of reference ERETIC ((2)H-ERETIC-NMR) has been applied to this compound. A(i) measurements have been performed on 19 samples of methyl salicylate from different origins, natural/synthetic and commercial/extracted. This study demonstrates that appropriate treatment performed on the data allows discrimination between synthetic and natural samples. Moreover, the representation of intramolecular ratios R(6/5) as a function of R(3/2) distinguishes between synthetics, wintergreen oils, and sweet birch bark oils. PMID:15969485

Le Grand, Flore; George, Gerard; Akoka, Serge

2005-06-29

74

Two new organic reference materials for ??13C and ??15N measurements and a new value for the ?? 13C of NBS 22 oil  

USGS Publications Warehouse

Analytical grade L-glutamic acid is chemically stable and has a C/N mole ratio of 5, which is close to that of many of natural biological materials, such as blood and animal tissue. Two L-glutamic acid reference materials with substantially different 13C and 15N abundances have been prepared for use as organic reference materials for C and N isotopic measurements. USGS40 is analytical grade L-glutamic acid and has a ?? 13C value of -26.24??? relative to VPDB and a ?? 15N value of +4.52??? relative to N2 in air. USGS41 was prepared by dissolving analytical grade L-glutamic acid with L-glutamic acid enriched in 13C and 15N. USGS41 has a ?? 13C value of +37.76??? and a ??15N value of +47.57???. The ??13C and ??15N values of both materials were measured against the international reference materials NBS 19 calcium carbonate (??13C = +1.95???), L-SVEC lithium carbonate (??13C = -46.48???), IAEA-N-1 ammonium sulfate (??15N=0.43???), and USGS32 potassium nitrate (?? 15N = 180???) by on-line combustion continuous-flow and off-line dual-inlet isotope-ratio mass spectrometry. Both USGS40 and USGS41 are isotopically homogeneous; reproducibility of ??13C is better than 0.13???, and that of ??15N is better than 0. 13??? in 100-??g amounts. These two isotopic reference materials can be used for (i) calibrating local laboratory reference materials, and (ii) quantifying drift with time, mass-dependent fractionations, and isotope-ratio-scale contraction in the isotopic analysis of various biological materials. Isotopic results presented in this paper yield a ?? 13C value for NBS 22 oil of -29.91???, in contrast to the commonly accepted value of -29.78??? for which off-line blank corrections probably have not been quantified satisfactorily. Published in 2003 by John Wiley & Sons, Ltd.

Qi, H.; Coplen, T. B.; Geilmann, H.; Brand, W. A.; Bohlke, J. K.

2003-01-01

75

Nitrogen isotope compositions of the Cooma metamorphic complex, Australia: Implications for 15N-enriched reservoirs  

NASA Astrophysics Data System (ADS)

The well-studied Paleozoic (435 Ma) Cooma metamorphic complex is centered on the township of Cooma 110 km south of Canberra, Australia. It is characterized by a uniform siliciclastic protolith, with a range of metamorphic grade from lowest-grade greenschist- to highest-grade granulite facies; the metamorphic zone index minerals are chlorite, biotite, andalusite, and sillimanite, and migmatite (Johnson and Vernon, 1995). Accordingly, it provides a natural window to investigate the variations of nitrogen concentrations and ? 15N values during prograde metamorphism. Nitrogen contents decrease, whereas ? 15N increase through progressive metamorphic zones from slates containing 250 ppm N, ? 15N = 2.4 permil; through chlorite zone (greenschist facies) with 210 ppm N, ? 15N = 3.2 permil; and the biotite and andalusite zones (amphibolite facies) having 130 ppm N, ? 15N = 3.8 permil, and 125 ppm N, ? 15N = 4.3 permil, respectively; to the sillimanite and migmatite zones (granulate facies) with 71 ppm N, ? 15N = 12.3 permil, and 77 ppm N, ? 15N = 12.9 permil, respectively. These results show: (1) only small ? 15N shifts of 1 to 2 permil from lower greenschist to amphibolite facies metamorphism, consistent with previous empirical studies of the Catalina Schist Complex (Bebout and Fogel, 1992) and the Erzgebirge terrane (Mingram and Brauer, 2001), and experimental studies on the fractionation of nitrogen isotopes (Ader et al., 1998); and (2) large fractionations of 8 to 10% at granulite facies. Low-grade N systematics can be explained by N2-NH4+ exchange at temperatures of 300 to 600oC for Rayleigh distillation or Batch devolatilization, whereas high-grade shifts can be interpreted as NH3-NH4+ exchanges at temperature of 600-730oC using equilibrium models. Archean cherts, at greenschist facies, show a range of ? 15N from -6 to +30 permil, where depleted values have been interpreted as primary, indicative of reducing conditions, and enriched values as metamorphic shifts Beaumont and Robert, 1999; Pinti et al., 2001). The results rule out those interpretations of metamorphic shifts, but rather a ? 15N-enriched reservoir exists (Jia and Kerrich, 2004), as well as locally oxic conditions from low Th/U ratios in 2.7 Ga shales (Jia et al., 2003).

Jia, Y.

2004-05-01

76

A selective 15N-to-(1)H polarization transfer sequence for more sensitive detection of 15N-choline.  

PubMed

The sensitivity and information content of heteronuclear nuclear magnetic resonance is frequently optimized by transferring spin order of spectroscopic interest to the isotope of highest detection sensitivity prior to observation. This strategy is extended to 15N-choline using the scalar couplings to transfer polarization from 15N to choline's nine methyl 1H spins in high field. A theoretical analysis of a sequence using nonselective pulses shows that the optimal efficiency of this transfer is decreased by 62% as the result of competing 15N-(1)H couplings involving choline's four methylene protons. We have therefore incorporated a frequency-selective pulse to support evolution of only the 15N-methyl 1H coupling during the transfer period. This sequence provides a 52% sensitivity enhancement over the nonselective version in in vitro experiments on a sample of thermally polarized 15N-choline in D2O. Further, the 15N T1 of choline in D2O was measured to be 217+/-38 s, the 15N-methyl 1H coupling constant was found to be 0.817+/-0.001 Hz, and the larger of choline's two 15N-methylene 1H coupling constants was found to be 3.64+/-0.0 1Hz. Possible improvements and applications to in vivo experiments using long-lived hyperpolarized heteronuclear spin order are discussed. PMID:20472478

Pfeilsticker, Jessica A; Ollerenshaw, Jason E; Norton, Valerie A; Weitekamp, Daniel P

2010-07-01

77

Natural abundance 17O NMR study of 2- and 4-substituted benzoyl chlorides  

NASA Astrophysics Data System (ADS)

Natural abundance 17O NMR chemical shift data for 17 ortho and para benzoyl chlorides recorded in acetonitrile at 75°C are reported. 17O NMR data for the para substituted benzoyl chlorides are correlated with 17O NMR data for similarly substituted acetophenones and methyl benzoates. The 17O NMR signals for ortho isomers are downfield ( ca 30 ppm) from their para isomers; the downfield shifts are consistent with torsion angle change. The 17O NMR data for the para isomers gave good correlations with ? + constants and with dual substituent parameters (DSP).

Boykin, David W.

78

Enantioselective syntheses of ?-amino-?-hydroxy acids, [ 15 N]- L-allo threonine and [ 15N]-L-threonine  

Microsoft Academic Search

The enantioselective synthesis of [15N]-L-allothreonine from ethyl (S)-lactatevia methyl (S)-3-methoxymethoxy-2-oxobutanoate15 is described. The stereogenic centre at C-2 was established by a one-pot, dual enzyme catalysed hydrolysis of the ester (by a lipase) and reductive amination of the ketone of 15 (with leucine dehydrogenase) to give, after deprotection, [15N]-(2S,3S)-2-amino-3-hydroxybutanoic acid as a single diastereomer in 93% yield. [15N]-L-Threonine was prepared by

Andrew Sutherland; Christine L. Willis

1997-01-01

79

Reactions, characterization and uptake of ammoxidized kraft lignin labeled with 15N.  

PubMed

Ammoxidation of kraft lignin was carried out in a Parr reactor using (15)NH(3) as the main nitrogen source. Reaction parameters were set up until a total nitrogen content of approximately 13 wt.% in lignin was achieved, in accordance with conditions of previous studies. Analytical tools such as FTIR, Py-GC/MS, and solid state NMR were used in this research. The nature of nitrogen bondings is discussed. The incorporation of the (15)N from ammoxidized lignin was followed in pumpkins (Zucchini cucurbita pepo L.) by means of (15)N emission spectroscopy. PMID:17161600

Ramírez, F; Varela, G; Delgado, E; López-Dellamary, F; Zúñiga, V; González, V; Faix, O; Meier, D

2007-05-01

80

A selective 15N-to-1H polarization transfer sequence for more sensitive detection of 15N-choline  

Microsoft Academic Search

The sensitivity and information content of heteronuclear nuclear magnetic resonance is frequently optimized by transferring spin order of spectroscopic interest to the isotope of highest detection sensitivity prior to observation. This strategy is extended to 15N-choline using the scalar couplings to transfer polarization from 15N to choline's nine methyl 1H spins in high field. A theoretical analysis of a sequence

Jessica A. Pfeilsticker; Jason E. Ollerenshaw; Valerie A. Norton; Daniel P. Weitekamp

2010-01-01

81

A selective 15N-to- 1H polarization transfer sequence for more sensitive detection of 15N-choline  

Microsoft Academic Search

The sensitivity and information content of heteronuclear nuclear magnetic resonance is frequently optimized by transferring spin order of spectroscopic interest to the isotope of highest detection sensitivity prior to observation. This strategy is extended to 15N-choline using the scalar couplings to transfer polarization from 15N to choline’s nine methyl 1H spins in high field. A theoretical analysis of a sequence

Jessica A. Pfeilsticker; Jason E. Ollerenshaw; Valerie A. Norton; Daniel P. Weitekamp

2010-01-01

82

Phenylalanine ?15N in Paleo Archives as a New Proxy for ?15N of Exported Primary Production  

NASA Astrophysics Data System (ADS)

Compound-specific isotope analysis of individual amino acids (CSI-AA) is emerging as a powerful new tool for studying the paleo nitrogen cycle. Because most detrital organic nitrogen is composed of amino acids, CSI-AA can reveal the mechanistic basis for organic nitrogen diagenesis, preserve a record of past food web structure, and potentially reconstruct the ?15N values of past nitrate and primary production. Within the commonly measured amino acids, the ?15N value of phenylalanine (Phe) appears uniquely promising as a new proxy that reflects the nitrogen isotopic value of the original source. Phe ?15N values remain almost unchanged with trophic transfer through food webs, and also during at least the initial stages of organic matter degradation. Here we synthesize results from both bio-archives and recent sediments, which together suggest that at least in Holocene archives the Phe ?15N value does in fact record the average inorganic nitrogen ?15N value at the base of planktonic food webs. However, several important unknowns also remain. These include the extent of variation in amino acid isotopic fractionation patterns in phylogenetically distinct algal groups. The stability of Phe ?15N values in older sediments where organic matter has undergone extensive diagenesis is also an important research area, which may ultimately establish the temporal limit for application of this approach to study past geological epochs. Together, however, results to date suggest that of Phe ?15N values in paleo archives represent a novel molecular-level proxy which is not tied to any specific organism or group, but rather can provide an integrated estimate of ?15N value of exported primary production.

McCarthy, M.; Batista, F. C.; Vokhshoori, N. L.; Brown, J. T.; Guilderson, T. P.; Ravelo, A. C.; Sherwood, O.

2012-12-01

83

Differences in the fractional abundances of carbohydrates of natural and recombinant human tissue factor  

PubMed Central

Tissue factor (TF) is a single polypeptide integral membrane glycoprotein composed of 263 residues and is essential to life in its role as the initiator of blood coagulation. Objective Previously we have shown that the activity of the natural placental TF (pTF) and the recombinant TF (rTF) from Sf9 insect cells is different (Krudysz-Amblo, J. et al(2010) J. Biol. Chem. 285, 3371–3382). In this study, using mass spectrometry, we show by quantitative analysis that the extent of glycosylation varies on each protein. Results Fractional abundance, of each glycan composition at each of the three glycosylation sites, reveals the most pronounced difference to be at asparagine (Asn) 11. This residue is located in the region of extensive TFfactor VIIa (FVIIa) interaction. Carbohydrate fractional abundance at Asn11 revealed that glycosylation in the natural placental TF is much more prevalent (~76%) than in the recombinant protein (~20%). The extent of glycosylation on Asn124 and Asn137 is similar in the two proteins, despite the pronounced differences in the carbohydrate composition. Additionally, 77% of rTF exists as TF des-1, 2 (missing the first two amino acids from the N-terminus). In contrast, only 31% of pTF is found in the des-1, 2 form. Conclusion These observations may attribute to the difference in the ability of TF-FVIIa complex to activate factor X (FX). Structural and functional comparison of the recombinant and natural protein advances our understanding and knowledge on the biological activity of TF.

Krudysz-Amblo, Jolanta; Jennings, Mark E; Matthews, Dwight E; Mann, Kenneth G; Butenas, Saulius

2011-01-01

84

Using natural abundance of ?13C to partition ecosystem soil respiration  

NASA Astrophysics Data System (ADS)

Soil respiration constitutes a major component of the global carbon and is the single most important flux of CO2 from the terrestrial ecosystem. Recently assimilated (autotrophic) carbon and CO2 respired during microbial decomposition of older SOM (heterotrophic carbon) may differ in their response to environmental conditions. We make use of a natural stable carbon isotope differences (typically 2-4 ‰) between the CO2 from autotrophic respiration of roots and heterotrophic respiration of soil organic matter to partition total soil respiration in situ. We used a new, open steady-state chamber technique to measure the respiration rate and collect samples of soil surface CO2 efflux with minimal disturbance to the diffusion of 12CO2 and 13CO2 from the soil surface. Gas samples were collected in Tedlar bags and analysed with a tunable diode laser. We installed rings and at each ring the roots, litter and root-free soil were incubated in bags to determine the ?13C of the end members. During incubation ?13C became more depleted with time (5.2 ‰ after 8 h), so the initial value was calculated from a time course. The total flux was partitioned into two major sources. Two examples are presented of partitioning soil respiration in young forests using natural abundance ?13C discrimination. In a 23 year-old Kanuka forest, SOM was typically 5.5 ‰ enriched compared with the roots (-27.5 ‰). All 50 rings were successfully partitioned, resulting in a mean of 22 % of the soil surface respiration originated from SOM. In the young 4-year old Pinus radiata forest, SOM was again enriched (3.6 ‰) compared to the roots (-25.8‰). Some 42 % of the soil respiration was from SOM turnover. We have shown the possibility of using natural abundance ?13C discrimination to quantify the proportion of total soil respired CO2 originating from SOM turnover in young C3 forests.

Hunt, J.; Millard, P.; Midwood, A. J.; Whitehead, D.

2010-12-01

85

Organic vs. Conventional Grassland Management: Do 15N and 13C Isotopic Signatures of Hay and Soil Samples Differ?  

PubMed Central

Distinguishing organic and conventional products is a major issue of food security and authenticity. Previous studies successfully used stable isotopes to separate organic and conventional products, but up to now, this approach was not tested for organic grassland hay and soil. Moreover, isotopic abundances could be a powerful tool to elucidate differences in ecosystem functioning and driving mechanisms of element cycling in organic and conventional management systems. Here, we studied the ?15N and ?13C isotopic composition of soil and hay samples of 21 organic and 34 conventional grasslands in two German regions. We also used ??15N (?15N plant - ?15N soil) to characterize nitrogen dynamics. In order to detect temporal trends, isotopic abundances in organic grasslands were related to the time since certification. Furthermore, discriminant analysis was used to test whether the respective management type can be deduced from observed isotopic abundances. Isotopic analyses revealed no significant differences in ?13C in hay and ?15N in both soil and hay between management types, but showed that ?13C abundances were significantly lower in soil of organic compared to conventional grasslands. ??15N values implied that management types did not substantially differ in nitrogen cycling. Only ?13C in soil and hay showed significant negative relationships with the time since certification. Thus, our result suggest that organic grasslands suffered less from drought stress compared to conventional grasslands most likely due to a benefit of higher plant species richness, as previously shown by manipulative biodiversity experiments. Finally, it was possible to correctly classify about two third of the samples according to their management using isotopic abundances in soil and hay. However, as more than half of the organic samples were incorrectly classified, we infer that more research is needed to improve this approach before it can be efficiently used in practice.

Klaus, Valentin H.; Holzel, Norbert; Prati, Daniel; Schmitt, Barbara; Schoning, Ingo; Schrumpf, Marion; Fischer, Markus; Kleinebecker, Till

2013-01-01

86

Evaluating the source of streamwater nitrate using ??15N and ??18O in nitrate in two watersheds in New Hampshire, USA  

USGS Publications Warehouse

The natural abundance of nitrogen and oxygen isotopes in nitrate can be a powerful tool for identifying the source of nitrate in streamwater in forested watersheds, because the two main sources of nitrate, atmospheric deposition and microbial nitrification, have distinct ??18O values. Using a simple mixing model, we estimated the relative fractions in streamwater derived from these sources for two forested watersheds with markedly different streamwater nitrate outputs. In this study, we monitored ??15N and ?? 18O of nitrate biweekly in atmospheric deposition and in streamwater for 20 months at the Hubbard Brook Experimental Forest, New Hampshire, USA (moderate nitrogen export), and monthly in streamwater at the Bowl Research Natural Area, New Hampshire, USA (high nitrogen export). For rain, ??18O values ranged from +47 to +77??? (mean: +58???) and ??15N from -5 to +1??? (mean: -3???); for snow, ??18O values ranged from +52 to +75??? (mean: +67???) and ?? 15N from -3 to +2??? (mean: -1???). Streamwater nitrate, in contrast to deposition, had ?? 18O values between +12 and +33??? (mean: +18???) and ??15N between -3 and +6??? (mean: 0???). Since nitrate produced by nitrification typically has ?? 18O values ranging from -5 to +15???, our field data suggest that most of the nitrate lost from the watersheds in streamflow was nitrified within the catchment. Our results confirm the importance of microbial nitrogen transformations in regulating nitrogen losses from forested ecosystems and suggest that hydrologic storage may be a factor in controlling catchment nitrate losses. ?? 2004 John Wiley and Sons, Ltd.

Pardo, L. H.; Kendall, C.; Pett-Ridge, J.; Chang, C. C. Y.

2004-01-01

87

Natural-Abundance 43Ca Solid-State NMR Spectroscopy of Bone  

PubMed Central

Structural information about the coordination environment of calcium present in bone is highly valuable in understanding the role of calcium in bone formation, biomineralization, and bone diseases like osteoporosis. While a high-resolution structural study on bone has been considered to be extremely challenging, NMR studies on model compounds and bone minerals have provided valuable insights into the structure of bone. Particularly, the recent demonstration of 43Ca solid-state NMR experiments on model compounds is an important advance in this field. However, application of 43Ca NMR is hampered due to the low natural-abundance and poor sensitivity of 43Ca. In this study, we report the first demonstration of natural-abundance 43Ca magic angle spinning (MAS) NMR experiments on bone, using powdered bovine cortical bone samples. 43Ca NMR spectra of bovine cortical bone are analyzed by comparing to the natural-abundance 43Ca NMR spectra of model compounds including hydroxyapatite and carbonated apatite. While 43Ca NMR spectra of hydroxyapatite and carbonated apatite are very similar, they significantly differ from that of cortical bone. Raman spectroscopy shows that the calcium environment in bone is more similar to carbonated apatite than hydroxyapatite. A close analysis of 43Ca NMR spectra reveals that the chemical shift frequencies of cortical bone and 10% carbonated apatite are similar but the quadrupole coupling constant of cortical bone is larger than that measured for model compounds. In addition, our results suggest that an increase in the carbonate concentration decreases the observed 43Ca chemical shift frequency. A comparison of experimentally obtained 43Ca MAS spectra with simulations reveal a 3:4 mole ratio of Ca-I:Ca-II sites in carbonated apatite and a 2.3:3 mole ratio for hydroxyapatite. 2D triple-quantum 43Ca MAS experiments performed on a mixture of carbonated apatite and the bone protein osteocalcin reveal the presence of protein-bound and free calcium sites, which is in agreement with a model developed from X-ray crystal structure of the protein.

Xu, Jiadi; Zhu, Peizhi; Gan, Zhehong; Sahar, Nadder; Tecklenburg, Mary; Morris, Michael D.; Kohn, David H.; Ramamoorthy, Ayyalusamy

2010-01-01

88

Rivermouth alteration of agricultural impacts on consumer tissue ?(15)N.  

PubMed

Terrestrial agricultural activities strongly influence riverine nitrogen (N) dynamics, which is reflected in the ?(15)N of riverine consumer tissues. However, processes within aquatic ecosystems also influence consumer tissue ?(15)N. As aquatic processes become more important terrestrial inputs may become a weaker predictor of consumer tissue ?(15)N. In a previous study, this terrestrial-consumer tissue ?(15)N connection was very strong at river sites, but was disrupted by processes occurring in rivermouths (the 'rivermouth effect'). This suggested that watershed indicators of N loading might be accurate in riverine settings, but could be inaccurate when considering N loading to the nearshore of large lakes and oceans. In this study, the rivermouth effect was examined on twenty-five sites spread across the Laurentian Great Lakes. Relationships between agriculture and consumer tissue ?(15)N occurred in both upstream rivers and at the outlets where rivermouths connect to the nearshore zone, but agriculture explained less variation and had a weaker effect at the outlet. These results suggest that rivermouths may sometimes be significant sources or sinks of N, which would cause N loading estimates to the nearshore zone that are typically made at discharge gages further upstream to be inaccurate. Identifying definitively the controls over the rivermouth effect on N loading (and other nutrients) will require integration of biogeochemical and hydrologic models. PMID:23935980

Larson, James H; Richardson, William B; Vallazza, Jon M; Nelson, John C

2013-01-01

89

Rivermouth alteration of agricultural impacts on consumer tissue ?15N  

USGS Publications Warehouse

Terrestrial agricultural activities strongly influence riverine nitrogen (N) dynamics, which is reflected in the ?15N of riverine consumer tissues. However, processes within aquatic ecosystems also influence consumer tissue ?15N. As aquatic processes become more important terrestrial inputs may become a weaker predictor of consumer tissue ?15N. In a previous study, this terrestrial-consumer tissue ?15N connection was very strong at river sites, but was disrupted by processes occurring in rivermouths (the ‘rivermouth effect’). This suggested that watershed indicators of N loading might be accurate in riverine settings, but could be inaccurate when considering N loading to the nearshore of large lakes and oceans. In this study, the rivermouth effect was examined on twenty-five sites spread across the Laurentian Great Lakes. Relationships between agriculture and consumer tissue ?15N occurred in both upstream rivers and at the outlets where rivermouths connect to the nearshore zone, but agriculture explained less variation and had a weaker effect at the outlet. These results suggest that rivermouths may sometimes be significant sources or sinks of N, which would cause N loading estimates to the nearshore zone that are typically made at discharge gages further upstream to be inaccurate. Identifying definitively the controls over the rivermouth effect on N loading (and other nutrients) will require integration of biogeochemical and hydrologic models.

Larson, James H.; Richardson, William B.; Vallazza, Jon M.; Nelson, John C.

2013-01-01

90

On the nature of lithium-rich giant stars. Constraints from beryllium abundances  

NASA Astrophysics Data System (ADS)

We have derived beryllium abundances for 7 Li-rich giant (A(Li) > 1.5) stars and 10 other Li-normal giants with the aim of investigating the origin of the lithium in the Li-rich giants. In particular, we test the predictions of the engulfment scenario proposed by Siess & Livio (1999, MNRAS, 308, 1133), where the engulfment of a brown dwarf or one or more giant planets would lead to simultaneous enrichment of 7Li and 9Be. We show that regardless of their nature, none of the stars studied in this paper were found to have detectable beryllium. Using simple dilution arguments we show that engulfment of an external object as the sole source of Li enrichment is ruled out by the Li and Be abundance data. The present results favor the idea that Li has been produced in the interior of the stars by a Cameron-Fowler process and brought up to the surface by an extra mixing mechanism.

Melo, C. H. F.; de Laverny, P.; Santos, N. C.; Israelian, G.; Randich, S.; Do Nascimento, J. D., Jr.; de Medeiros, J. R.

2005-08-01

91

Investigating microbial carbon cycling using natural abundance isotope analysis of PLFA  

NASA Astrophysics Data System (ADS)

Understanding microbial carbon sources and cycling is fundamental to our conceptualization of microbial ecosystems and their role in biogeochemical cycling in natural systems. Achieving this understanding requires application of a wide range of approaches. Natural abundance isotope analysis of individual compounds, particularly cellular components such as Phospholipids Fatty Acids (PLFA) can provide insights into the carbon sources and metabolic activities of the in situ microbial community from environmental samples. This is primarily because specific PLFA can be well resolved by gas chromatography even from complex matrices where confounding biological/organic compound abound. These PLFA can then be attributed to the viable microbial community, in some cases to specific components of this community and due to characteristic biosynthetic fractionations of stable isotope ratios, ?13C analysis of PLFA can: differentiate isotopically distinct primary carbon sources of heterotrophic communities; identify isotopic patterns characteristic of autotrophic versus heterotrophic processes; and elucidate microbial biosynthetic pathways. In cases where there ?13C cannot provide resolution of carbon sources, new approaches in ?14C of PLFA can be applied. The vast range in ?14C of ancient and modern carbon provides an easily traceable signal that can differentiate uptake and utilization of these carbon sources. This is particularly useful in cases such as contaminated sites where petroleum based contamination has occurred, or in natural systems where microbial communities may be utilizing geologic versus recently photosynthetically fixed carbon. This talk will present several examples demonstrating the utility of this approach.

Slater, G. G.; Brady, A.; Cowie, B.

2008-12-01

92

The pure rotational spectrum of glycolaldehyde isotopologues observed in natural abundance  

NASA Astrophysics Data System (ADS)

The pure rotational spectrum of glycolaldehyde has been recorded from 6.5-20 GHz and 25-40 GHz in two pulsed-jet chirped pulse Fourier transform microwave spectrometers. The high phase stability of the spectrometers enables deep signal integration, allowing transitions from the 13C-substituted, 18O-substituted, and deuterium-substituted isotopologues to be observed in natural abundance. Transitions from HCOCH218OH are reported for the first time. Additional transitions from the 13C-substituted, deuterium-substituted, and HC18OCH2OH isotopologues, as well as previously unobserved weak lines from the main isotopologue, have been observed. Transitions from all isotopologues are used with previously reported transitions to refine the spectroscopic parameters for each isotopologue. A Kraitchman analysis was performed using the experimental rotational constants to determine the molecular structure of glycolaldehyde.

Brandon Carroll, P.; McGuire, Brett A.; Zaleski, Daniel P.; Neill, Justin L.; Pate, Brooks H.; Widicus Weaver, Susanna L.

2013-02-01

93

Automated determination of silicon isotope natural abundance by the acid decomposition of cesium hexafluosilicate.  

PubMed

A procedure for the automated determination of isotopic abundances of silicon from biogenic and lithogenic particulate matter and from dissolved silicon in fresh or saltwaters is reported. Samples are purified using proven procedures through the reaction of Si with acidified ammonium molybdate, followed by precipitation with triethylamine and combustion of the precipitate to yield silicon dioxide. The silicon dioxide is converted to cesium hexafluosilicate by dissolution in hydrogen fluoride and the addition of cesium chloride. Isotopic analysis is accomplished by decomposing the cesium hexafluosilicate with concentrated sulfuric acid to generate silicon tetrafluoride gas. Silicon tetrafluoride is purified cryogenically and analyzed on a gas source isotope ratio mass spectrometer. Yields of silicon tetrafluoride are >99.5%. The procedure can be automated by modifying commercial inlet systems designed for carbonate analysis. The procedure is free of memory effects and isotopic biases. Reproducibility is +/-0.03-0.10 per thousand for a variety of natural and synthetic materials. PMID:16944891

Brzezinski, Mark A; Jones, Janice L; Beucher, Charlotte P; Demarest, Mark S; Berg, Howard L

2006-09-01

94

Apparent /sup 15/N uptake kinetics resulting from remineralization  

SciTech Connect

A computer model of phytoplankton /sup 15/N uptake experiments in which simultaneous remineralization is occurring is used to demonstrate potential artifacts if remineralization is disregarded. In simulated experiments where a range of /sup 15/N additions is made to obtain population kinetics, apparent kinetics can be obtained where none exist. Similarly, in simulated experiments where samples are taken over time there is an apparent decrease in uptake rates with time, which, when plotted against inferred changes in substrate concentration, gives rise to similar kinetics. In actual experiments, such artifacts could obscure any real kinetics and would lead to erroneous estimates of population characteristics.

Garside, C.

1984-01-01

95

Measurement of isotope abundance variations in nature by gravimetric spiking isotope dilution analysis (GS-IDA).  

PubMed

Subtle variations in the isotopic composition of elements carry unique information about physical and chemical processes in nature and are now exploited widely in diverse areas of research. Reliable measurement of natural isotope abundance variations is among the biggest challenges in inorganic mass spectrometry as they are highly sensitive to methodological bias. For decades, double spiking of the sample with a mix of two stable isotopes has been considered the reference technique for measuring such variations both by multicollector-inductively coupled plasma mass spectrometry (MC-ICPMS) and multicollector-thermal ionization mass spectrometry (MC-TIMS). However, this technique can only be applied to elements having at least four stable isotopes. Here we present a novel approach that requires measurement of three isotope signals only and which is more robust than the conventional double spiking technique. This became possible by gravimetric mixing of the sample with an isotopic spike in different proportions and by applying principles of isotope dilution for data analysis (GS-IDA). The potential and principle use of the technique is demonstrated for Mg in human urine using MC-TIMS for isotopic analysis. Mg is an element inaccessible to double spiking methods as it consists of three stable isotopes only and shows great potential for metabolically induced isotope effects waiting to be explored. PMID:23419016

Chew, Gina; Walczyk, Thomas

2013-04-01

96

On the nature of sn stars. I. A detailed abundance study  

NASA Astrophysics Data System (ADS)

The sn stars were first discoved by Abt & Levato when studying the spectral types in different open clusters. These stars present sharp Balmer lines, sharp metallic lines (C II, Si II, Ca II, Ti II, Fe II), and broad coreless He I lines. Some of the sn stars seem to be related to CP stars. Initially Abt & Levato proposed a shell-like nature to explain the sn stars, although this scenario was subsequently questioned. There is no general agreement about their origin. We aim to derive abundances for a sample of 9 stars, including sn and non-sn stars, to determine the possible relation between sn and CP stars and compare their chemical abundances. That most sn stars belong to open clusters allows us to search for a possible relation with fundamental parameters, including the age and rotation. We also study the possible contribution of different effects to the broad He I lines observed in these stars, such as Stark broadening and the possible He-stratification. Effective temperature and gravity were estimated by Strömgren photometry and then refined by requiring ionization and excitation equilibrium of Fe lines. We derived the abundances by fitting the observed spectra with synthetic spectra using an iterative procedure with the SYNTHE and ATLAS9 codes. We derived metallic abundances of 23 different chemical elements for 9 stars and obtained low projected rotational velocities for the sn stars in our sample (vsini up to 69 km s-1). We also compared 5 stars that belong to the same cluster (NGC 6475) and show that the sn characteristics appear in the 3 stars with the lower rotational velocity. However, the apparent preference of sn stars for objects with the lower vsini values should be taken with caution due to the small number of objects studied here. We analysed the photospheric chemical composition of sn stars and show that approximately ~40% of them display chemical peculiarities (such as He-weak and HgMn stars) within a range of temperature of 10 300 K-14 500 K. However, there are also sn stars with solar or nearly-solar (i.e. non-CP) chemical composition. We have studied the possible contribution of different processes to the broad He I lines present in the sn stars. Although NLTE effects could not be completely ruled out, it seems that NLTE is not directly related to the broad He I profiles observed in the sn stars. The broad-line He I 4026 Å is the clearest example of the sn characteristics in our sample. We succesfully fit this line in 4 out of 7 sn stars by using the appropriate Stark broadening tables, while small differences appear in the other 3 stars. Studying the plots of abundance vs. depth for the He I lines resulted in some sn stars probably being stratified in He. However, a further study of variability in the He I lines would help for determining whether a possible non-uniform He superficial distribution could also play a role in these sn stars. We conclude that the broad He I lines that characterize the sn class could be modelled (at least in some of these stars) by the usual radiative transfer process with Stark broadening, without needing another broadening mechanism. The observed line broadening in sn stars seems to be related to the "normal" He line formation that originates in these atmospheres.

Saffe, C.; Levato, H.

2014-02-01

97

15N/14N variations in Cretaceous Atlantic sedimentary sequences: implication for past changes in marine nitrogen biogeochemistry  

USGS Publications Warehouse

At two locations in the Atlantic Ocean (DSDP Sites 367 and 530) early to middle Cretaceous organic-carbon-rich beds ("black shales") were found to have significantly lower ??15N values (lower 15N/14N ratios) than adjacent organic-carbon-poor beds (white limestones or green claystones). While these lithologies are of marine origin, the black strata in particular have ??15N values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools. In contrast, black, organic-carbon-rich beds at a third site (DSDP Site 603) contain predominantly terrestrial organic matter and have C- and N-isotopic compositions similar to organic matter of modern terrestrial origin. The recurring 15N depletion in the marine-derived Cretaceous sequences prove that the nitrogen they contain is the end result of an episodic and atypical biogeochemistry. Existing isotopic and other data indicate that the low 15N relative abundance is the consequence of pelagic rather than post-depositional processes. Reduced ocean circulation, increased denitrification, and, hence, reduced euphotic zone nitrate availability may have led to Cretaceous phytoplankton assemblages that were periodically dominated by N2-fixing blue-green algae, a possible source of this sediment 15N-depletion. Lack of parallel isotopic shifts in Cretaceous terrestrially-derived nitrogen (Site 603) argues that the above change in nitrogen cycling during this period did not extend beyond the marine environment. ?? 1987.

Rau, G. H.; Arthur, M. A.; Dean, W. E.

1987-01-01

98

Rapid mass spectrometric analysis of 15N-Leu incorporation fidelity during preparation of specifically labeled NMR samples  

PubMed Central

Advances in NMR spectroscopy have enabled the study of larger proteins that typically have significant overlap in their spectra. Specific 15N-amino acid incorporation is a powerful tool for reducing spectral overlap and attaining reliable sequential assignments. However, scrambling of the label during protein expression is a common problem. We describe a rapid method to evaluate the fidelity of specific 15N-amino acid incorporation. The selectively labeled protein is proteolyzed, and the resulting peptides are analyzed using MALDI mass spectrometry. The 15N incorporation is determined by analyzing the isotopic abundance of the peptides in the mass spectra using the program DEX. This analysis determined that expression with a 10-fold excess of unlabeled amino acids relative to the 15N-amino acid prevents the scrambling of the 15N label that is observed when equimolar amounts are used. MALDI TOF-TOF MS/MS data provide additional information that shows where the “extra” 15N labels are incorporated, which can be useful in confirming ambiguous assignments. The described procedure provides a rapid technique to monitor the fidelity of selective labeling that does not require a lot of protein. These advantages make it an ideal way of determining optimal expression conditions for selectively labeled NMR samples.

Truhlar, Stephanie M.E.; Cervantes, Carla F.; Torpey, Justin W.; Kjaergaard, Magnus; Komives, Elizabeth A.

2008-01-01

99

Trophic niche differentiation in soil microarthropods (Oribatida, Acari): evidence from stable isotope ratios ( 15N\\/ 14N)  

Microsoft Academic Search

The large number of animals that coexist in soil without any clear niche differentiation has puzzled biologists for a long time. We investigated stable isotope ratios (15N\\/14N) in a diverse group of soil microarthropods, oribatid mites, to evaluate trophic niche differentiation. The natural variation of the stable isotopes 15N\\/14N was measured in 36 species\\/taxa from four beech and beech-oak forests.

Katja Schneider; Sonja Migge; Roy A. Norton; Stefan Scheu; Reinhard Langel; August Reineking; Mark Maraun

2004-01-01

100

Stepwise enrichment of 15N along food chains: Further evidence and the relation between ? 15N and animal age  

NASA Astrophysics Data System (ADS)

The isotopic composition of nitrogen was measured in marine and fresh-water animals from the East China Sea, The Bering Sea, Lake Ashinoko and Usujiri intertidal zone. Primary producers, showed average ?15Nversus atmospheric nitrogen of +5.0%. (+3.4 to +7.5) in the Bering Sea and Lake Ashinoko, and +6.8%. (+6.0 to +7.6) in Usujiri intertidal zone. Blue green algae from the East China Sea show an average -0.55%. (-0.8 to +1.2). All consumers, Zooplankton, fish and bird exhibited Stepwise enrichment of 15N with increasing trophic level. The 15N enrichment at a single feeding process ranged from +1.3 to +5.3 averaging +3.4 ± 1.1%.. This isotopic fractionation seems to be independent of habitat. The effect of age in animals was obtained by analyzing two marine mussels. The soft tissue nitrogen showed +2.0%. enrichment relative to that of primary producers, and the magnitude was almost constant with shell ages ranging from 0 to 8 years. A similar 15N enrichment occurs in all Molluscs, Crustaceans, Insecta, Amphibia, Fish, Ave and Mammal species regardless of the difference in the form of excreted nitrogen and in laboratory cultured fish, brine shrimp and mice (+2.9 to +4.9%.). The excreted ammonia from guppy was sufficiently light to balance the concentration of 15N to animal body.

Minagawa, Masao; Wada, Eitaro

1984-05-01

101

Natural abundance high field (43)Ca solid state NMR in cement science.  

PubMed

This work is a systematic attempt to determine the possibilities and the limitations of the (43)Ca high field solid state NMR in the study of cement-based materials. The low natural abundance (0.135%) and small gyromagnetic ratio of (43)Ca present a serious challenge even in a high magnetic field. The NMR spectra of a number of cement compounds of known structure and composition are examined. The spectra of several phases important in cement science, e.g., anhydrous beta di-calcium silicate (beta-C(2)S) and tri-calcium (C(3)S) silicate were obtained for the first time and the relation of spectroscopic and structural parameters is discussed. The method was also applied to the hydrated C(3)S and synthetic calcium silicate hydrates (C-S-H) of different composition in order to understand the state of calcium and transformations in the structure during hydrolysis. The spectra of hydrated C(3)S reveals a calcium environment similar to that of the C-S-H samples and 11 A Tobermorite. These observations support the validity of using layered crystalline C-S-H systems as structural models for the C-S-H that forms in the hydration of Portland cement. PMID:20463996

Moudrakovski, Igor L; Alizadeh, Rouhollah; Beaudoin, James J

2010-07-14

102

Calibration of an elastic recoil setup for D/H-ratios close to natural abundance  

NASA Astrophysics Data System (ADS)

Nominally Anhydrous Minerals (NAM) in the Earth's mantle contain trace amounts of hydrogen, as a result of the NAM's ability to incorporate hydroxyl ions. The isotopic composition of these hydrogen reservoirs is for the Earth's crust, well characterized. The knowledge of the isotopic composition of the Earth's interior on the other hand is limited. It is believed that the hydrogen composition in the interior is isotopically heterogeneous and that there may exist several reservoirs of hydrogen, characterized by different deuterium/hydrogen-ratios. Characterization of these hydrogen reservoirs can provide valuable information about the mass transport of hydrogen during the evolution of the planet. In this work we present a variant of the proton-proton scattering technique with which we are capable of performing simultaneous measurements of deuterium and hydrogen. The method has been tested with a 2.9 MeV deuteron beam on a polyethylene standard, with D/H ratio close to the natural abundance, and on a thin sample of Muscovite with a hydrogen concentration of 4800 wt-ppm. This is followed by a discussion about limitations and capabilities of the technique.

Ros, L.; Borysiuk, M.; Kristiansson, P.; Abdel, N.; Elfman, M.; Nilsson, E. J. C.; Pallon, J.

2014-08-01

103

?15N in the turtle grass from the Mexican Caribbean  

NASA Astrophysics Data System (ADS)

Nutrient inputs associated with population growth threaten the integrity of coastal ecosystems. To assess the rapid increase in tourism, we compared the ?15N from Thalassia testudinum collected at sites with different levels of tourism development and population to detect the N inputs of wastewater discharge (WD) along the coast of Quintana Roo. The contributions of nitrogen enriched in 15N are directly related to the increase of WD inputs in areas of high tourism development (Nichupte Lagoon in Cancun, >3 million tourists per year from 2007 to 2011 and 0.7 million of resident population) and decreased towards Bahia Akumal and Tulum (>3 million tourists per year from 2007 to 2011 and 0.15 million of resident population). The ?15N from T. testudinum was significantly lower at Mahahual and Puerto Morelos (about 0.4 million tourists per year in 2007 to 2011 and 0.25 million of resident population) than other the sites. In areas of the lowest development and with tourist activity restricted and small population, such as the Yum Balam Reserve and Sian Ka'an Biosphere Reserve, the ?15N values were in much higher enrichment that Mahahual and Puerto Morelos. Therefore is suggested that Mahahual and Puerto Morelos may be used for baseline isotopic monitoring, over environmental pressure on the reef lagoon ecosystem, where tourist activities and population are growing very slow rate. The anthropogenic N input has the potential to impact, both environmentally and economically, the seagrass meadows and the coral reefs along the coast of Quintana Roo and the Caribbean.

Talavera-Saenz, A.; Sanchez, A.; Ortiz-Hernandez, M.

2013-05-01

104

(15)N chemical shift referencing in solid state NMR.  

PubMed

Solid-state NMR spectroscopy has much advanced during the last decade and provides a multitude of data that can be used for high-resolution structure determination of biomolecules, polymers, inorganic compounds or macromolecules. In some cases the chemical shift referencing has become a limiting factor to the precision of the structure calculations and we have therefore evaluated a number of methods used in proton-decoupled (15)N solid-state NMR spectroscopy. For (13)C solid-state NMR spectroscopy adamantane is generally accepted as an external standard, but to calibrate the (15)N chemical shift scale several standards are in use. As a consequence the published chemical shift values exhibit considerable differences (up to 22ppm). In this paper we report the (15)N chemical shift of several commonly used references compounds in order to allow for comparison and recalibration of published data and future work. We show that (15)NH4Cl in its powdered form (at 39.3ppm with respect to liquid NH3) is a suitable external reference as it produces narrow lines when compared to other reference compounds and at the same time allows for the set-up of cross-polarization NMR experiments. The compound is suitable to calibrate magic angle spinning and static NMR experiments. Finally the temperature variation of (15)NH4Cl chemical shift is reported. PMID:24746715

Bertani, Philippe; Raya, Jésus; Bechinger, Burkhard

2014-01-01

105

Paleoenvironmental implications of taxonomic variation among ? 15 N values of chloropigments  

NASA Astrophysics Data System (ADS)

Natural variations in the ratios of nitrogen isotopes in biomass reflect variations in nutrient sources utilized for growth. In order to use ? 15N values of chloropigments of photosynthetic organisms to determine the corresponding ? 15N values of biomass - and by extension, surface waters - the isotopic offset between chlorophyll and biomass must be constrained. Here we examine this offset in various geologically-relevant taxa, grown using nutrient sources that may approximate ocean conditions at different times in Earth's history. Phytoplankton in this study include cyanobacteria (diazotrophic and non-diazotrophic), eukaryotic algae (red and green), and anoxygenic photosynthetic bacteria (Proteobacteria), as well as environmental samples from sulfidic lake water. Cultures were grown using N 2, NO 3-, and NH 4+ as nitrogen sources, and were examined under different light regimes and growth conditions. We find surprisingly high variability in the isotopic difference (? 15N biomass - ? 15N chloropigment) for prokaryotes, with average values for species ranging from -12.2‰ to +11.7‰. We define this difference as ?por, a term that encompasses diagenetic porphyrins and chlorins, as well as chlorophyll. Negative values of ?por reflect chloropigments that are 15N-enriched relative to biomass. Notably, this enrichment appears to occur only in cyanobacteria. The average value of ?por for freshwater cyanobacterial species is -9.8 ± 1.8‰, while for marine cyanobacteria it is -0.9 ± 1.3‰. These isotopic effects group environmentally but not phylogenetically, e.g., ?por values for freshwater Chroococcales resemble those of freshwater Nostocales but differ from those of marine Chroococcales. Our measured values of ?por for eukaryotic algae (range = 4.7-8.7‰) are similar to previous reports for pure cultures. For all taxa studied, values of ?por do not depend on the type of nitrogen substrate used for growth. The observed environmental control of ?por suggests that values of ?por could be useful for determining the fractional burial of eukaryotic vs. cyanobacterial organic matter in the sedimentary record.

Higgins, Meytal B.; Wolfe-Simon, Felisa; Robinson, Rebecca S.; Qin, Yelun; Saito, Mak A.; Pearson, Ann

2011-11-01

106

Population abundance of Frankliniella occidentalis (Thysanoptera: Thripidae) and natural enemies on plant hosts in central Chile.  

PubMed

Populations of the invasive Frankliniella occidentalis (Pergande) are serious pests of agricultural crops in the Aconcagua Valley of central Chile. An extensive survey was conducted of 55 plant species in 24 families to identify plant hosts of F. occidentalis and to determine its relative abundance on each host during each season. A more intensive study was conducted on selected plant species serving as reproductive hosts to determine the population dynamics of F. occidentalis and to evaluate the potential importance of Orius species and other natural enemies for controlling F. occidentalis. Adults of F. occidentalis were active during each season of the year inhabiting the flowers of 91% of the sampled plant species in 22 families, and 86% of these plant species in 19 families served as reproductive hosts. The number of host plant species used was greatest in the spring and least in the winter. All of the hosts except Medicago sativa L. were used only when flowering. Populations of F. occidentalis were significantly aggregated in M. sativa in the terminal buds over the leaves when the host was not flowering, and in the flowers, followed by the terminal buds, followed by the leaves when the host was flowering. Larvae were 1.3-2.3 times more abundant on dates when M. sativa was flowering. There were no identifiable patterns in plant hosts based on endemicity or plant family. Most of the plant species used by F. occidentalis were inferior quality hosts where populations either declined or were stable. Populations of F. occidentalis on low-quality hosts generally escaped predation by Orius species and competition by other species of thrips. Only 25% of the food hosts and 28% of the reproductive hosts for F. occidentalis in the extensive survey, respectively, were host plants for Orius. Parasitoids and other predators were not found to be important in suppressing thrips on any of the plant hosts. Populations of F. occidentalis increased on only a few hosts, including M. sativa and Sisymbrium officinale L. Scop. These apparently are major sources of F. occidentalis adults invading crops. We conclude that F. occidentalis is established in central Chile and that it has replaced and possibly displaced the native Frankliniella australis (Morgan) as the most common thrips species. PMID:19389281

Ripa, Renato; Funderburk, Joe; Rodriguez, Fernando; Espinoza, Fernanda; Mound, Laurence

2009-04-01

107

Soil organic matter stability in agricultural land: New insights using ?15N, ?13C and C:N ratio  

NASA Astrophysics Data System (ADS)

Soil organic matter (SOM) contains three times more carbon than in the atmosphere or terrestrial vegetation. This major pool of organic carbon is sensitive to climate change, but the mechanisms for carbon stabilization in soils are still not well understood and the ultimate potential for carbon stabilization is unknown. For predicting SOM dynamics, it is necessary to gain information on the turnover rates or stability of different soil organic carbon pools. The common method to determine stability and age of SOM is the 14C radio carbon technique, which is very expensive and therefore limited in use. Conen et al. (2008) developed a model to estimate the SOM stability based on the isotopic discrimination of 15N natural abundance by soil micro-organisms, and the decreasing C:N ratio during organic matter decomposition. This model has been developed for permanent grasslands in the Swiss Alps under steady-state conditions. The objective of our study was to validate whether this model could be used or adapted, in combination with 13C isotope signatures of SOM, to predict the relative age and stability of SOM fractions in more disturbed agricultural ecosystems. The present study was carried out on soils collected from six long-term experimental trials (from 12 to 50 years) under different agricultural management practices (e.g. no tillage vs conventional tillage, and mulch, fertilizer, green or animal manure application), located in Austria, Belgium, Kenya and China. Top and subsoil were sampled until 80-100 cm depth. Particulate organic matter (POM) fraction was obtained by wet sieving (> 63?m) after sonification and density separation (<1.8 g cm?3). Carbon and nitrogen contents and their stable isotopic ratios (i.e. 15N and 13C) were measured in POM and bulk soils. The mineral associated matter fraction (mOM), as the protected carbon, was calculated by difference to the bulk soil organic carbon. The relative age of the SOM was calculated using the Conen model and preliminary validated by 14C dating. At all sites, the POM has a higher C:N ratio and a lower ?15N signature compared to the mOM fraction. The POM in top soil layers (<30 cm) has a lower C:N ratio than in deep soil. The C:N ratio and ?15N of POM was influenced by agricultural management. The mOM fraction has 53 to 2063 times longer turnover rate than POM, the relative age of the SOM raised with increasing soil depth. The combination of the above results with ?13C data lead to a more comprehensive understanding of the processes underlying SOM dynamics. Tillage practices increased the bulk ?13C signature of the SOM in the deeper subsoil, suggesting the presence of more stable decomposed materials. The results of this research seem to indicate that the model, developed for grasslands, can be used to determine the stability of SOM in agricultural ecosystems. The C:N ratio and ?15N signature of the POM and mOM fraction follow the expected model pattern. The isotopic ?13C signature can further enhance the understanding of the processes driving SOM stability.

Mao, Yanling; Heiling, Maria; De Clercq, Tim; Resch, Christian; Aigner, Martina; Mayr, Leo; Vanlauwe, Bernard; Thuita, Moses; Steier, Peter; Leifeld, Jens; Merckx, Roel; Spiegel, Heide; Cepuder, Peter; Nguyen, Minh-Long; Zaman, Mohammad; Dercon, Gerd

2014-05-01

108

Natural abundance-level measurement of the nitrogen isotopic composition of oceanic nitrate: an adaptation of the ammonia diffusion method  

Microsoft Academic Search

We have adapted the “ammonia diffusion” method of nitrate extraction for natural-abundance level nitrogen isotopic measurement of oceanic nitrate. The method involves: (1) sample concentration (by boiling or evaporation); (2) conversion of nitrate to ammonia using Devarda's alloy; and (3) the gas-phase diffusion of ammonia onto an acidified glass fiber disk which is sandwiched between two porous Teflon membranes. We

D. M. Sigman; M. A. Altabet; R. Michener; D. C. McCorkle; B. Fry; R. M. Holmes

1997-01-01

109

The Determination of the Natural Abundance of the Isotopes of Chlorine: An Introductory Experiment in Mass Spectrometry.  

ERIC Educational Resources Information Center

Describes a laboratory experiment which introduces basic principles and experimental techniques of mass spectrometry for fourth year undergraduate (B.Sc.) students. Laboratory procedures, background information, and discussion of results are provided for the experiment in which the natural isotopic abundance of chlorine is determined. (Author/JN)

O'Malley, Rebecca M.

1982-01-01

110

Nitrification of 15 N -ammonium sulphate and crop recovery of 15 N -labelled ammonium nitrates injected in bands  

Microsoft Academic Search

The influence of fertiliser incorporation and band injection on immobilisation and nitrification of ammonium-nitrogen (N) was investigated in a bare soil field experiment. Total and inorganic forms of 15N in the 0–20cm soil layer were measured on days 0, 7 and 16 after (15NH4)2SO4 application in framed micro-plots. Injection of the nitrogen fertiliser in a concentrated band reduced immobilisation, leaving

J. Petersen; B. Hansen; P. Sørensen

2004-01-01

111

Stepwise enrichment of 15 N along food chains: Further evidence and the relation between 15 N and animal age  

Microsoft Academic Search

The isotopic composition of nitrogen was measured in marine and fresh-water animals from the East China Sea, The Bering Sea, Lake Ashinoko and Usujiri intertidal zone. Primary producers, showed average 15 N versus atmospheric nitrogen of +5.0%. (+3.4 to +7.5) in the Bering Sea and Lake Ashinoko, and +6.8%. (+6.0 to +7.6) in Usujiri intertidal zone. Blue green algae from

Masao Minagawa; Eitaro Wada

1984-01-01

112

Estimation of natural mortality coefficient from fish abundance and catch data using Virtual Population Analysis (VPA)  

NASA Astrophysics Data System (ADS)

Natural mortality coefficient ( M) was estimated from fish abundance ( N) and catch ( C) data using a Virtual Population Analysis (VPA) model. Monte Carlo simulations were used to evaluate the impact of different error distributions for the simulated data on the estimates of M. Among the four error structures (normal, lognormal, Poisson and gamma), simulations of normally distributed errors produced the most viable estimates for M, with the lowest relative estimation errors (REEs) and median mean absolute deviations (MADs) for the ratio of the true to the estimated Ms. In contrast, the lognormal distribution had the largest REE value. Errors with different coefficients of variation (CV) were added to N and C. In general, when CVs in the data were less than 10%, reliable estimates of M were obtained. For normal and lognormal distributions, the estimates of M were more sensitive to the CVs in N than in C; when only C had error the estimates were close to the true. For Poisson and gamma distributions, opposite results were obtained. For instance, the estimates were more sensitive to the CVs in C than in N, with the largest REE from the scenario of error only in C. Two scenarios of high and low fishing mortality coefficient ( F) were generated, and the simulation results showed that the method performed better for the scenario with low F. This method was also applied to the published data for the anchovy ( Engraulis japonicus) of the Yellow Sea. Viable estimates of M were obtained for young groups, which may be explained by the fact that the great uncertainties in N and C observed for older Yellow Sea anchovy introduced large variation in the corresponding estimates of M.

Wang, Yingbin; Liu, Qun; Wang, Yanjun

2007-01-01

113

COVALENT BINDING OF REDUCED METABOLITES OF [15N3] TNT TO SOIL ORGANIC MATTER DURING A BIOREMEDIATION PROCESS ANALYZED BY 15N NMR SPECTROSCOPY. (R826646)  

EPA Science Inventory

Evidence is presented for the covalent binding of biologically reduced metabolites of 2,4,6-15N3-trinitrotoluene (TNT) to different soil fractions (humic acids, fulvic acids, and humin) using liquid 15N NMR spectroscopy. A silylation p...

114

Tracer studies on dinoflagellate luciferin with [ 15N]-glycine and [ 15N]- l-glutamic acid in the dinoflagellate Pyrocystis lunula  

Microsoft Academic Search

The bioluminescence of dinoflagellate is a typical luciferin–luciferase reaction. To clarify the biosynthesis of dinoflagellate luciferin, we performed a feeding experiment with [15N]-glycine and [15N]-l-glutamic acid in the dinoflagellate Pyrocystis lunula. In a control experiment, we also examined whether or not chlorophyll a was incorporated with these labeled compounds. We detected by mass spectrometry the incorporation of [15N]-glycine and [15N]-l-glutamic

Chun Wu; Hidetoshi Akimoto; Yoshihiro Ohmiya

2003-01-01

115

Precursors of glutamic acid nitrogen in primary neuronal cultures: Studies with 15 N  

Microsoft Academic Search

We utilized gas chromatography-mass spectrometry to study the transfer of15N from [2-15N]glutamine, [15N]leucine, [15N]alanine, or15NH4Cl to [15N]glutamate and [15N]aspartate in cultured cerebrocortical GABA-ergic neurons from the mouse. Initial rates of15N appearance (atom % excess) were somewhat higher with 2mM [2-15N]glutamine as a precursor than with 1mM [15N]leucine or 1mM [15N]alanine, but initial net formation (nmol [15N]glutamate\\/mg protein.min-1) was roughly comparable

Marc Yudkoff; Itzhak Nissim; Leif Hertz

1990-01-01

116

The fellowship of natural abundance 2H-isotopomers of monoterpenes.  

PubMed

Site-specific natural abundance hydrogen isotope ratios have been measured by deuterium-NMR in a wide variety of monoterpenes from numerous kinds of plants grown in different environments. Once the NMR signals have been assigned to the whole sets of isotopomers in the different molecules and schemes of connections to the parent isotopomers in the geranyl diphosphate (GPP) precursor have been defined, a very consistent set of isotopic profiles is evidenced. The results, which are incompatible with the mevalonate pathway, can be satisfactorily interpreted by considering the deoxyxylulose pathway (DOXP), which is now recognized as the usual route for monoterpene biosynthesis in plants. Strong deuterium depletion at ex-site 2 of GPP, accompanied by high isotope ratio values at site ex-6, are consistent with synthesis of GPP from isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) molecules independently produced by the DOXP pathway. However, for a given molecular species, significant differences are observed as a function of the plant source, in particular at site ex-6 of GPP. Thus, monoterpenes from plants with a C3 metabolism are mostly characterized by relatively high values of (D/H)6, whereas C4 plants tend to show much lower values. This behavior may be attributed to more or less significant contributions of GPP resulting from the condensation of IPP with DMAPP produced by isomerization. The isotopic profile therefore enables the role of physiological and environmental factors on the relative importance of the "independent" and "isomerized" model to be estimated. More generally, isotope ratios at individual sites in geraniol can be traced back to the corresponding sites in GPP, then to sites of the IPP and DMAPP building blocks, then to the pyruvate and glyceraldehyde 3-phosphate DOXP active molecules, and finally to the carbohydrate photosynthetic precursor. Furthermore, the methylenic hydrogen atoms, which are enantiotopic in geraniol, become diastereotopic in chiral, and more specially in cyclic, monoterpenes. This provides an isotopic verification for the complete stereochemical chain of affiliation, and a way of estimating enantiomeric purity and whether intermolecular exchanges have taken place. PMID:15474569

Martin, Gérard J; Lavoine-Hanneguelle, Sophie; Mabon, Françoise; Martin, Maryvonne L

2004-10-01

117

Accurate rest frequencies for the submillimetre-wave lines of the 15{N}-containing isotopologues of N2H+ and N2D^+  

NASA Astrophysics Data System (ADS)

The submillimetre-wave spectrum of the molecular ions N15NH^+, 15NNH^+, N15ND^+, and 15NND+ have been investigated in the laboratory using a source-modulation microwave spectrometer equipped with a negative glow discharge cell. The diazenylium ion was produced in a Ar/N2/H2(D2) discharge plasma and the 15N-containing isotopologues were observed in natural abundance. Six new rotational transitions for the protonated species and seven for the deuterated ones were accurately measured in the frequency range 270-760 GHz. These new laboratory measurements of the rare isotopologues of N2H+ provide very precise rest frequencies at millimetre and submillimetre wavelengths useful for the radioastronomical identification of their rotational lines in the ISM.

Dore, L.; Bizzocchi, L.; Degli Esposti, C.; Tinti, F.

2009-03-01

118

Ureide assay for measuring nitrogen fixation by nodulated soybean calibrated by sup 15 N methods. [Glycine max  

SciTech Connect

We report experiments to quantify the relationships between the relative abundance of ureide-N in root-bleeding sap, vacuum-extracted sap, and hot water extracts of stems and petioles of nodulated soybean (Glycine max (L.) Merrill cv Bragg) and the proportion of plant N derived from nitrogen fixation. Additional experiments examined the effects of plant genotype and strain of rhizobia on these relationships. In each of the five experiments reported, plants of cv Bragg (experiment 1), cv Lincoln (experiments 3, 4, 5), or six cultivars/genotypes (experiment 2) were grown in a sand:vermiculite mixture in large pots in a naturally lit, temperature-controlled glasshouse during summer. Pots were inoculated at sowing with effective Bradyrhizobium japonicum CB 1809 (USDA 136) or with one of 21 different strains of rhizobia. The proportions of plant N derived from nitrogen fixation were determined using {sup 15}N dilution. Results show that assessment of nitrogen fixation by soybean using the ureide technique should now be possible with the standard curves presented, irrespective of genotype or strain of rhizobia occupying the nodules.

Herridge, D.F. (New South Wales Agriculture Fisheries, Tamworth (Australia)); Peoples, M.B. (CSIRO Division of Plant Industry, Canberra (Australia))

1990-06-01

119

Studies of physicochemical properties of NH•••N hydrogen bonds in DNA, using selective 15N-labeling and direct 15N 1D NMR  

Microsoft Academic Search

15N-15N scalar coupling constants across base pair hydrogen bonds (2hJNN) were studied using residue- and atom-specifically 15N labeled DNA oligomers. The N3 atom selectively 15N enriched 2'-deoxycytidine and thymidine, and the uniformly 15N enriched 2'-deoxyadenosine and 2'-deoxyguanosine, were chemically prepared and incorporated into two DNA oligomers, d(CGCGAATTCGCG)2 and d(CGCAAAAAGCG)•d(CGCTTTTTGCG). This isotope labeling enabled us to determine the 2hJNN value from

Chojiro Kojima; Akira Ono; Masatsune Kainosho

2000-01-01

120

Is the multicolored Asian ladybeetle, Harmonia axyridis, the most abundant natural enemy to aphids in agroecosystems?  

PubMed

The multicolored Asian ladybeetle, Harmonia axyridis Pallas (Coleoptera: Coccinellidae), was introduced into Western Europe in the late 1990s. Since the late 2000s, this species has been commonly considered one of the most abundant aphid predators in most Western European countries. In spite of the large amount of research on H. axyridis, information concerning its relative abundance in agroecosystems is lacking. This study aims to evaluate the abundance of H. axyridis within the aphidophage community in four crops situated in southern Belgium: wheat, Triticum aestivum L. (Poales: Poaceae), corn, Zea mays, potato, Solanum tuberosum (Solanales: Solanaceae), and broad bean Vicia faba (Fabales: Fabaceae). In order to assess the species diversity, the collected data were analyzed by considering (1) the species richness and (2) the evenness according to the Shannon diversity index. Eleven aphidophages were observed in every inventoried agroecosystem, including five abundant species: three coccinellids, the seven-spotted ladybug, Coccinella septempunctata L. (Coleoptera: Coccinellidae), the 14-spotted Ladybird, Propylea quatuordecimpunctata, and H. axyridis; one hoverfly, the marmalade hoverfly, Episyrphus balteatus De Geer (Diptera: Syrphidae); and one lacewing, the common green lacewing, Chrysoperla carnea Stephens sensu lato (= s.l.) (Neuroptera: Chrysopidae). Harmonia axyridis has been observed to thrive, breed, and reproduce on the four studied crops. Harmonia axyridis is the most abundant predator of aphids in corn followed by C. septempunctata, which is the main aphid predator observed in the three other inventoried crops. In wheat and potato fields, H. axyridis occurs in low numbers compared to other aphidophage. These observations suggest that H. axyridis could be considered an invasive species of agrosystems, and that potato and wheat may intermittently act as refuges for other aphidophages vulnerable to intraguild predation by this invader. Harmonia axyridis is not the most abundant aphid predator in the main Belgian crops. PMID:24785375

Vandereycken, Axel; Durieux, Delphine; Joie, Emilie; Sloggett, John J; Haubruge, Eric; Verheggen, François J

2013-01-01

121

Is the Multicolored Asian Ladybeetle, Harmonia axyridis, the Most Abundant Natural Enemy to Aphids in Agroecosystems?  

PubMed Central

The multicolored Asian ladybeetle, Harmonia axyridis Pallas (Coleoptera: Coccinellidae), was introduced into Western Europe in the late 1990s. Since the late 2000s, this species has been commonly considered one of the most abundant aphid predators in most Western European countries. In spite of the large amount of research on H. axyridis, information concerning its relative abundance in agroecosystems is lacking. This study aims to evaluate the abundance of H. axyridis within the aphidophage community in four crops situated in southern Belgium: wheat, Triticum aestivum L. (Poales: Poaceae), corn, Zea mays, potato, Solanum tuberosum (Solanales: Solanaceae), and broad bean Vicia faba (Fabales: Fabaceae). In order to assess the species diversity, the collected data were analyzed by considering (1) the species richness and (2) the evenness according to the Shannon diversity index. Eleven aphidophages were observed in every inventoried agroecosystem, including five abundant species: three coccinellids, the seven-spotted ladybug, Coccinella septempunctata L. (Coleoptera: Coccinellidae), the 14-spotted Ladybird, Propylea quatuordecimpunctata, and H. axyridis; one hoverfly, the marmalade hoverfly, Episyrphus balteatus De Geer (Diptera: Syrphidae); and one lacewing, the common green lacewing, Chrysoperla carnea Stephens sensu lato (= s.l.) (Neuroptera: Chrysopidae). Harmonia axyridis has been observed to thrive, breed, and reproduce on the four studied crops. Harmonia axyridis is the most abundant predator of aphids in corn followed by C. septempunctata, which is the main aphid predator observed in the three other inventoried crops. In wheat and potato fields, H. axyridis occurs in low numbers compared to other aphidophage. These observations suggest that H. axyridis could be considered an invasive species of agrosystems, and that potato and wheat may intermittently act as refuges for other aphidophages vulnerable to intraguild predation by this invader. Harmonia axyridis is not the most abundant aphid predator in the main Belgian crops.

Vandereycken, Axel; Durieux, Delphine; Joie, Emilie; Sloggett, John J.; Haubruge, Eric; Verheggen, Francois J.

2013-01-01

122

Nitrogen mineralization, denitrification, and nitrate ammonification by soil-feeding termites: a 15 N-based approach  

Microsoft Academic Search

Soil-feeding termites are abundant and play important roles in the biogeochemical processes in tropical soils. Previous studies\\u000a indicated that they preferentially utilize the peptidic components of soil organic matter as a nutrient resource. Here, we\\u000a determined the corresponding mineralization fluxes and elucidated other N transformation processes that occur during soil\\u000a gut passage using 15N tracer techniques. Termite-based rates of N

David Kamanda Ngugi; Rong Ji; Andreas Brune

2011-01-01

123

Assignment of 15N chemical shifts and 15N relaxation measurements for oxidized and reduced iso-1-cytochrome c.  

PubMed

A protocol for complete isotopic labeling of iso-1-cytochrome c from the eukaryote Saccharomyces cerevisiae is reported. Assignments are reported for the vast majority of the 15N amide resonances in both oxidized and reduced states. 15N heteronuclear relaxation experiments were collected to study the picosecond-nanosecond backbone dynamics of this protein. Relaxation rates were computed and fit to spectral density functions by a model-free analysis. Backbone amides in the overlapping loop B/C region are the most flexible on the picosecond-nanosecond time scale in both forms of the protein. The results show that, on average, the protein backbone is slightly more dynamic in the oxidized than the reduced state, though not significantly so. Exchange terms, which suggest significant motion on a time scale at least an order of magnitude slower than the overall correlation time of 5.2 ns, were required for only two residues in the reduced state and 27 residues in the oxidized state. When analyzed on a per-residue basis, the lower order parameters found in the oxidized state were scattered throughout the protein, with a few continuous segments found in loop C and the C-terminal helix, suggesting greater flexibility of these regions in the oxidized state. The results provide dynamic interpretations for previously presented structural and functional data, including redox-dependent changes that occur in the protein. The way is now paved for extensive dynamic analysis of variant cytochromes c. PMID:10194370

Fetrow, J S; Baxter, S M

1999-04-01

124

Theoretical and experimental 1H, 13C and 15N NMR studies of N-alkylation of substituted tetrazolo[1,5-a]pyridines.  

PubMed

The (15)N as well as (1)H and (13)C chemical shifts of nine substituted tetrazolopyridines and their corresponding tetrazolopyridinium salts have been determined by using NMR spectroscopy at the natural abundance level of all nuclei in CD(3)CN. In this paper, we report, for the first time, the N-alkylation reaction of electron deficient tetrazolopyridines. The treatment of tetrazolopyridines 5-13 with one equivalent of trialkyloxonium tetrafluoroborate leads to a mixture of two isomers, i.e. N3- and N2-alkyl tetrazolo[1,5-a]pyridinium salts. It has been observed that the N3-isomer is always the major isomer, except in the case of the CF(3) substituent, where the two isomers are obtained in the same amount. The quaternary tetrazolopyridinium nitrogen N3 is shielded by around 100 ppm (parts per million) with respect to the parent tetrazolopyridine. Experimental data are interpreted by means of density functional theory (DFT) calculations, including solvent-induced effects, within the conductor-like polarizable continuum model (CPCM). Good agreements between theoretical and experimental (1)H, (13)C and (15)N NMR were found. The combination of multinuclear magnetic resonance spectroscopy with gauge including atomic orbital (GIAO) DFT calculations is a powerful tool in the structural elucidation for both neutral and cationic heterocycles and in the determination of the orientation of N-alkylation of tetrazolopyridines. PMID:19937909

Berionni, Guillaume; Pégot, Bruce; Goumont, Régis

2010-02-01

125

Nitrate turnover in a peat soil under drained and rewetted conditions: results from a [(15)N]nitrate-bromide double-tracer study.  

PubMed

Under natural conditions, peatlands are generally nitrate-limited. However, recent concerns about an additional N input into peatlands by atmospheric N deposition have highlighted the risk of an increased denitrification activity and hence the likelihood of a rise of emissions of the greenhouse gas nitrous oxide. Therefore, the aim of the present study was to investigate the turnover of added nitrate in a drained and a rewetted peatland using a [(15)N]nitrate-bromide double-tracer method. The double-tracer method allows a separation between physical effects (dilution, dispersion and dislocation) and microbial and chemical nitrate transformation by comparing with the conservative Br(-) tracer. In the drained peat site, low NO3(-) consumption rates have been observed. In contrast, NO3(-) consumption at the rewetted peat site rises rapidly to about 100% within 4 days after tracer application. Concomitantly, the (15)N abundances of nitrite and ammonium in soil water increased and lead to the conclusion that, besides commonly known NO3(-) reduction to nitrite (i.e. denitrification), a dissimilatory nitrate reduction to ammonium has simultaneously taken place. The present study reveals that increasing NO3(-) inputs into rewetted peatlands via atmospheric deposition results in a rapid NO3(-) consumption, which could lead to an increase in N2O emissions into the atmosphere. PMID:24313368

Russow, Rolf; Tauchnitz, Nadine; Spott, Oliver; Mothes, Sibylle; Bernsdorf, Sabine; Meissner, Ralph

2013-01-01

126

Nitrogen-containing compounds in two CR2 meteorites: 15N composition, molecular distribution and precursor molecules  

NASA Astrophysics Data System (ADS)

Amino acids, amines and aldehydes were obtained from the water extracts of two CR2 carbonaceous chondrites from Antarctica and analyzed for their molecular and 15N isotopic content. These compounds were found to differ significantly from those of CM chondrites in both overall abundances and molecular distribution. The amino acids suites comprise a preponderant abundance of linear, 2-H amino acids, show rapid non-linear decrease with the compounds' increasing chain length and include protein amino acids never identified in meteorites before, such as threonine, tyrosine and phenylalanine. The presence of tertiary amines as well as a diverse, large abundance of aldehydes and ketones also distinguishes both CR2 organic suites. The ? 15N values determined for CR2 amino acids have a distribution between molecular subgroups that is opposite to the one of their ?D values, with 2-H amino acids having higher ? 15N and lower ?D values than 2-methyl amino acids, while the opposite is true for 2-methyl amino acids. Based on theoretical data, these isotopic findings would place the formation of the two amino acid groups or their direct precursors at different ISM stages of star formation.

Pizzarello, Sandra; Holmes, William

2009-04-01

127

Maize planting time and arthropod abundance in southern Mindanao, Philippines. II. Population dynamics of natural enemies  

Microsoft Academic Search

Beneficial arthropods were monitored in monthly plantings over 4 years in a rainfed, triple-maize cropping system in southern Mindanao, Philippines. Generalist predators and two egg parasitoids of the Asian corn borer Ostrinia furnacalis (Guenée) (ACB) did not show significant differences in abundance with respect to calendar month of planting over 39 crops. Two species of Trichogramma (T. evanescens Westwood and

J. A. Litsinger; C. G. Dela Cruz; B. L. Canapi; A. T. Barrion

2007-01-01

128

Ground-state photoneutron reactions in /sup 15/N  

SciTech Connect

Photoneutron angular distributions were measured by time-of-flight techniques for the reaction /sup 15/N(..gamma..,n/sub 0/) /sup 14/N over the region of excitation energy from 15 to 25 MeV. Ground state cross sections were obtained by stepping the bremsstrahlung end point over the energy region of interest in 2 MeV intervals. By fitting the spectral data to a series of Legendre polynomials, angular distribution coefficients were extracted and interpreted on the basis of a simple single particle model. It appears that a large fraction of the photoabsorption strength leading to decays via the ground state channel is due to the formation of J/sup ..pi../ = (3/2)/sup +/, T = (1/2) states in /sup 15/N which decay by d-wave neutron emission. The data support an approximation of purely electric dipole absorption in the region measured. Some small amount of s-wave neutron emission interfering with the dominant p/sub 1/2/..-->..d/sub 3/2/ transition is consistent with an observed value for the a/sub 2//a/sub 0/ coefficient of -0.7 +- 0.2. The (..gamma..,n/sub 0/) cross section integrated between threshold and 30 MeV is estimated to represent about one-third of the total strength in the neutron channel. A state identified at 17.3 MeV is consistent in energy and composition with a theoretical prediction based on a shell model calculation using a residual interaction with a Soper mixture of exchange forces.

Watson, J.D.; Jury, J.W.; Kuo, P.C.; Davidson, W.F.; Sherman, N.K.; McNeill, K.G.

1983-02-01

129

Flow and habitat effects on juvenile fish abundance in natural and altered flow regimes  

USGS Publications Warehouse

Conserving biological resources native to large river systems increasingly depends on how flow-regulated segments of these rivers are managed. Improving management will require a better understanding of linkages between river biota and temporal variability of flow and instream habitat. However, few studies have quantified responses of native fish populations to multiyear (>2 yr) patterns of hydrologic or habitat variability in flow-regulated systems. To provide these data, we quantified young-of-year (YOY) fish abundance during four years in relation to hydrologic and habitat variability in two segments of the Tallapoosa River in the southeastern United States. One segment had an unregulated flow regime, whereas the other was flow-regulated by a peak-load generating hydropower dam. We sampled fishes annually and explored how continuously recorded flow data and physical habitat simulation models (PHABSIM) for spring (April-June) and summer (July-August) preceding each sample explained fish abundances. Patterns of YOY abundance in relation to habitat availability (median area) and habitat persistence (longest period with habitat area continuously above the long-term median area) differed between unregulated and flow-regulated sites. At the unregulated site, YOY abundances were most frequently correlated with availability of shallow-slow habitat in summer (10 species) and persistence of shallow-slow and shallow-fast habitat in spring (nine species). Additionally, abundances were negatively correlated with 1-h maximum flow in summer (five species). At the flow-regulated site, YOY abundances were more frequently correlated with persistence of shallow-water habitats (four species in spring; six species in summer) than with habitat availability or magnitude of flow extremes. The associations of YOY with habitat persistence at the flow-regulated site corresponded to the effects of flow regulation on habitat patterns. Flow regulation reduced median flows during spring and summer, which resulted in median availability of shallow-water habitats comparable to the unregulated site. However, habitat persistence was severely reduced by flow fluctuations resulting from pulsed water releases for peak-load power generation. Habitat persistence, comparable to levels in the unregulated site, only occurred during summer when low rainfall or other factors occasionally curtailed power generation. As a consequence, summer-spawning species numerically dominated the fish assemblage at the flow-regulated site; five of six spring-spawning species occurring at both study sites were significantly less abundant at the flow-regulated site. Persistence of native fishes in flow-regulated systems depends, in part, on the seasonal occurrence of stable habitat conditions that facilitate reproduction and YOY survival.

Freeman, M.C.; Bowen, Z.H.; Bovee, K.D.; Irwin, E. R.

2001-01-01

130

[15N,1H]\\/[13C,1H]-TROSY for simultaneous detection of backbone 15N–1H, aromatic 13C–1H and side-chain 15N–1H2 correlations in large proteins  

Microsoft Academic Search

This paper describes a [15N,1H]\\/[13C,1H]-TROSY experiment for the simultaneous acquisition of the heteronuclear chemical shift correlations of backbone amide 15N–1H groups, side chain 15N–1H2 groups and aromatic 13C–1H groups in otherwise highly deuterated proteins. The 15N–1H and 13C–1H correlations are extracted from two subspectra of the same data set, thus preventing possible spectral overlap of aromatic and amide protons in

Konstantin Pervushin; Daniel Braun; César Fernández; Kurt Wüthrich

2000-01-01

131

Natural Abundance of Mass 47 in CO2 Emitted in Car Exhaust and Human Breath  

NASA Astrophysics Data System (ADS)

Atmospheric CO2 is widely studied using records of concentration, ? 13C and ? 18O, although the number and variability of sources and sinks prevents these alone from uniquely defining the budget. CO2 of mass 47 (mainly 13C18O16O) provides an additional potential tracer, but little is known about its ability to differentiate among various budget components. We present study of differences in 13C18O16O abundance between combustion and respiration. We define ? 47 as the difference in permil between the measured R47 (=[mass 47]/[mass 44]) and R47 expected for CO2 whose isotopes are distributed randomly among all isotopologues. Previous studies have shown that ? 47 values at thermodynamic equilibrium vary between zero at 1000\\deg C and 0.9\\permil at room temperature, raising the possibility that it could differentiate between CO2 produced by high temperature processes, such as combustion, and that produced in respiration. Values of ? 47 are non-linear in mixing. Therefore, it is useful to discuss the ? 47=(R47/R47ST-1)1000, where R47ST is the R47 expected for CO2 having ? 13C-VPDB=0, ? 18O-VSMOW=0 and ? 47=0. We used a Keeling plot approach to estimate ? 13C, ? 18O, ? 47 and ? 47 in CO2 from car exhaust and from human breath. Air sampled at 10am in the Caltech campus in Pasadena, CA, varied in CO2 concentration from 383 to 404ppm, in ? 13C and ? 18O from -9.2 to -10.2\\permil and from 40.7 to 42.0\\permil, respectively, in ? 47 of from 32.6 to 34.0\\permil, and in ? 47 from 0.73 to 0.96\\permil. We then sampled at varying distances from a car exhaust pipe. The intercepts in Keeling plots defined by these data, reflecting the car exhaust end-member, were similar to the values obtained very close to the exhaust pipe: ? 13C was found to equal -24.4±0.2\\permil, similar to the measured value of the gasoline used; ? 18O =30.0±0.4\\permil; ? 47=6.7±0.6\\permil; and ? 47=0.41±0.03\\permil. Both ? 18O and ? 47 are consistent with that expected for thermodynamic equilibrium at 200\\deg C between water and CO2 generated by combustion of gasoline-air mixtures. This temperature is lower than that of the catalytic converter, suggesting re-equilibration in the cooling exhaust as it travels through the tail pipe. This can explain why the ? 18O of CO2 from car exhaust is substantially greater than that of O2 in air. Samples of CO2 in human breath had ? 13C and ? 18O values broadly similar to those of car exhaust (-22.3±0.2 and 34.4±0.3\\permil, respectively), ? 47 of 13.5±0.4\\permil, but ? 47 of 0.74±0.02\\permil, far higher than exhaust and similar to that of background Pasadena air. ? 13C of human breath is similar to that of car exhaust, much as other respiration and fossil-fuel sources of CO2 generally overlap. Similarly, ? 18O of human breath and soil respiration are close to that of car exhaust. Therefore, conventional stable isotope constraints do not easily differentiate fossil-fuel and respiratory sources. In contrast, the ? 47 value of CO2 from car exhaust is easily differentiated from those of CO2 in human breath, largely due to enhanced thermodynamic stability of 13C18O16O at the low temperatures characteristic of respiration. Hence, ? 47 is a potentially useful tracer to distinguish anthropogenic, mostly combustion, CO2 sources from natural, low temperature, sources.

Affek, H. P.; Eiler, J. M.

2004-12-01

132

Automated protein turnover calculations from 15N partial metabolic labeling LC/MS shotgun proteomics data.  

PubMed

Protein turnover is a well-controlled process in which polypeptides are constantly being degraded and subsequently replaced with newly synthesized copies. Extraction of composite spectral envelopes from complex LC/MS shotgun proteomics data can be a challenging task, due to the inherent complexity of biological samples. With partial metabolic labeling experiments this complexity increases as a result of the emergence of additional isotopic peaks. Automated spectral extraction and subsequent protein turnover calculations enable the analysis of gigabytes of data within minutes, a prerequisite for systems biology high throughput studies. Here we present a fully automated method for protein turnover calculations from shotgun proteomics data. The approach enables the analysis of complex shotgun LC/MS 15N partial metabolic labeling experiments. Spectral envelopes of 1419 peptides can be extracted within an hour. The method quantifies turnover by calculating the Relative Isotope Abundance (RIA), which is defined as the ratio between the intensity sum of all heavy (15N) to the intensity sum of all light (14N) and heavy peaks. To facilitate this process, we have developed a computer program based on our method, which is freely available to download at http://promex.pph.univie.ac.at/protover. PMID:24736476

Lyon, David; Castillejo, Maria Angeles; Staudinger, Christiana; Weckwerth, Wolfram; Wienkoop, Stefanie; Egelhofer, Volker

2014-01-01

133

Automated Protein Turnover Calculations from 15N Partial Metabolic Labeling LC/MS Shotgun Proteomics Data  

PubMed Central

Protein turnover is a well-controlled process in which polypeptides are constantly being degraded and subsequently replaced with newly synthesized copies. Extraction of composite spectral envelopes from complex LC/MS shotgun proteomics data can be a challenging task, due to the inherent complexity of biological samples. With partial metabolic labeling experiments this complexity increases as a result of the emergence of additional isotopic peaks. Automated spectral extraction and subsequent protein turnover calculations enable the analysis of gigabytes of data within minutes, a prerequisite for systems biology high throughput studies. Here we present a fully automated method for protein turnover calculations from shotgun proteomics data. The approach enables the analysis of complex shotgun LC/MS 15N partial metabolic labeling experiments. Spectral envelopes of 1419 peptides can be extracted within an hour. The method quantifies turnover by calculating the Relative Isotope Abundance (RIA), which is defined as the ratio between the intensity sum of all heavy (15N) to the intensity sum of all light (14N) and heavy peaks. To facilitate this process, we have developed a computer program based on our method, which is freely available to download at http://promex.pph.univie.ac.at/protover.

Lyon, David; Castillejo, Maria Angeles; Staudinger, Christiana; Weckwerth, Wolfram; Wienkoop, Stefanie; Egelhofer, Volker

2014-01-01

134

Compound-Specific ?15N Amino Acid Measurements in Littoral Mussels in the California Upwelling Ecosystem: A New Approach to Generating Baseline ?15N Isoscapes for Coastal Ecosystems  

PubMed Central

We explored ?15N compound-specific amino acid isotope data (CSI-AA) in filter-feeding intertidal mussels (Mytilus californianus) as a new approach to construct integrated isoscapes of coastal primary production. We examined spatial ?15N gradients in the California Upwelling Ecosystem (CUE), determining bulk ?15N values of mussel tissue from 28 sites between Port Orford, Oregon and La Jolla, California, and applying CSI-AA at selected sites to decouple trophic effects from isotopic values at the base of the food web. Bulk ?15N values showed a strong linear trend with latitude, increasing from North to South (from ?7‰ to ?12‰, R2?=?0.759). In contrast, CSI-AA trophic position estimates showed no correlation with latitude. The ?15N trend is therefore most consistent with a baseline ?15N gradient, likely due to the mixing of two source waters: low ?15N nitrate from the southward flowing surface California Current, and the northward transport of the California Undercurrent (CUC), with15N-enriched nitrate. This interpretation is strongly supported by a similar linear gradient in ?15N values of phenylalanine (?15NPhe), the best AA proxy for baseline ?15N values. We hypothesize ?15NPhe values in intertidal mussels can approximate annual integrated ?15N values of coastal phytoplankton primary production. We therefore used ?15NPhe values to generate the first compound-specific nitrogen isoscape for the coastal Northeast Pacific, which indicates a remarkably linear gradient in coastal primary production ?15N values. We propose that ?15NPhe isoscapes derived from filter feeders can directly characterize baseline ?15N values across major biochemical provinces, with potential applications for understanding migratory and feeding patterns of top predators, monitoring effects of climate change, and study of paleo- archives.

Vokhshoori, Natasha L.; McCarthy, Matthew D.

2014-01-01

135

Quantitative Community Fingerprinting Methods for Estimating the Abundance of Operational Taxonomic Units in Natural Microbial Communities?  

PubMed Central

Molecular fingerprinting techniques offer great promise for analyzing changes in microbial community structure, especially when dealing with large number of samples. However, a serious limitation has been the lack of quantification offered by such techniques since the relative abundances of the identified operational taxonomic units (OTUs) in the original samples are not measured. A quantitative fingerprinting approach designated “qfingerprinting” is proposed here. This method involves serial dilutions of the sample of interest and further systematic fingerprinting of all dilution series. Using the ultimate dilutions for which OTU are still PCR amplifiable and taking into account peak size inaccuracy and peak reproducibility, the relative abundance of each OTU is then simultaneously determined over a scale spanning several orders of magnitude. The approach was illustrated by using a quantitative version of automated ribosomal intergenic spacer analysis (ARISA), here called qARISA. After validating the concept with a synthetic mixture of known DNA targets, qfingerprinting was applied to well-studied marine sediment samples to examine specific changes in OTU abundance associated with sediment depth. The new strategy represents a major advance for the detailed quantitative description of specific OTUs within complex communities. Further ecological applications of the new strategy are also proposed.

Ramette, Alban

2009-01-01

136

Using natural isotopic abundances to determine the source of nitrous oxide (N2O) emissions  

NASA Astrophysics Data System (ADS)

Numerous greenhouse gas studies have focused on carbon dioxide (CO2), whereas nitrous oxide (N2O) also plays a major role in global warming. Indeed, while nitrous oxide is 1000 times less concentrated than CO2 in the atmosphere, it is 300 times more efficient in terms of global warming potential. In addition, its atmospheric concentration increases with 0,3 % per year. According to the literature, nitrous oxide is produced, in soils and sediments, by two major processes: (1) Nitrification, mediated by autotrophic nitrifying bacteria under oxic conditions; (2) Denitrification, mediated by heterotrophic denitrifying bacteria under anoxic conditions. Denitrification induces intensive, localized and instantaneous fluxes. N2O emissions can be easily measured and modeled. In contrast, nitrification induces weak emissions, but spatially and temporally extended. Therefore, this process could represent a large potential of N2O emissions from soils and sediments. The study of isotopomer's isotopic composition of N2O, i.e. the intramolecular distribution or site preference (SP) determined by 15N measurement allows the determination of the origin of N2O emissions (nitrification vs. denitrification). Recent studies on pure cultures have showed that SP associated with nitrification is 35 ‰ while SP associated with denitrification is 0 ‰. The aim of this study was to determine SP associated with denitrification in soils and sediments, taking into account the environmental denitrifying bacterial communities, and under different environmental variables. To this end, flow-through reactors were used to determine denitrification rates at different temperatures and varying substrate (nitrate) concentrations. Site preference was measured for the different experiments. Different experiments of denitrification were realized in sediment flow through reactors under denitrifying conditions (anoxia, presence of organic matter and nitrate). We used acetylene (25°C) to block the enzyme nitrous oxide reductase, resulting in accumulation of N2O originating only from denitrification. Despite the fact that the isotopic composition of the produced N2O (15N and 18O) varies, the SP did not change significantly (SP = 6 ‰). These results compared to those of chemical denitrification show that despite very different isotopic compositions, the SP value is independent of the type of denitrification. Different nitrate concentrations (5 mM, 3 mM, 1,5 mM and 1 mM) at ambient temperature (25°C). The results of N2O production kinetics were not related to nitrate concentrations. SP of N2O are currently being analyzed. Different temperatures (35°C, 25°C and 12°C) and a nitrate concentration of 5 mM. The results of N2O production kinetics at different temperatures show an increase in N2O emissions with increasing temperature. SP of N2O are currently being analyzed. The goal for future work is to study the SP in these systems relative to salinity, pH and carbon organic concentration in denitrifying conditions but also in nitrifying conditions.

Mothet, A.; Sebilo, M.; Laverman, A. M.; Vaury, V.; Mariotti, A.

2012-04-01

137

Determining the Absolute Abundances of Natural Radioactive Elements on the Lunar Surface by the Kaguya Gamma-ray Spectrometer  

NASA Astrophysics Data System (ADS)

The Kaguya gamma-ray spectrometer (KGRS) has great potential to precisely determine the absolute abundances of natural radioactive elements K, Th and U on the lunar surface because of its excellent spectroscopic performance. In order to achieve the best performance of the KGRS, it is important to know the spatial response function (SRF) that describes the directional sensitivity of the KGRS. The SRF is derived by a series of Monte Carlo simulations of gamma-ray transport in the sensor of the KGRS using the full-fledged simulation model of the KGRS, and is studied in detail. In this paper, the method for deriving absolute abundance of natural radioactive elements based on the SRF is described for the analysis of KGRS data, which is also applicable to any gamma-ray remote sensings. In the preliminary analysis of KGRS data, we determined the absolute abundances of K and Th on the lunar surface without using any previous knowledge of chemical information gained from Apollo samples, lunar meteorites and/or previous lunar remote sensings. The results are compared with the previous measurements and the difference and the correspondence are discussed. Future detailed analysis of KGRS data will provide new and more precise maps of K, Th and U on the lunar surface.

Kobayashi, S.; Hasebe, N.; Shibamura, E.; Okudaira, O.; Kobayashi, M.; Yamashita, N.; Karouji, Y.; Hareyama, M.; Hayatsu, K.; D'Uston, C.; Maurice, S.; Gasnault, O.; Forni, O.; Diez, B.; Reedy, R. C.; Kim, K. J.

2010-07-01

138

Estimation of N(sub 2)-fixation in cowpea grown in monoculture or in mixture with maize using (sup 15) N.  

National Technical Information Service (NTIS)

A pot experiment was carried out under natural climatic conditions to determine the proportion of different nitrogen sources (air, soil, fertilizer) in cowpea and maize grown alone or in mixture using (sup 15) N isotope dilution technique. On average, the...

M. Shammaa F. Kurd Ali

1994-01-01

139

Solid state NMR studies of oligourea foldamers: interaction of 15N-labelled amphiphilic helices with oriented lipid membranes.  

PubMed

Synthetic oligomers that are derived from natural polypeptide sequences, albeit with unnatural building blocks, have attracted considerable interest in mimicking bioactive peptides and proteins. Many of those compounds adopt stable folds in aqueous environments that resemble protein structural elements. Here we have chemically prepared aliphatic oligoureas and labeled them at selected positions with (15)N for structural investigations using solid-state NMR spectroscopy. In the first step, the main tensor elements and the molecular alignment of the (15)N chemical shift tensor were analyzed. This was possible by using a two-dimensional heteronuclear chemical shift/dipolar coupling correlation experiment on a model compound that represents the chemical, and thereby also the chemical shift characteristics, of the urea bond. In the next step (15)N labeled versions of an amphipathic oligourea, that exert potent antimicrobial activities and that adopt stable helical structures in aqueous environments, were prepared. These compounds were reconstituted into oriented phospholipid bilayers and the (15)N chemical shift and (1)H-(15)N dipolar couplings of two labeled sites were determined by solid-state NMR spectroscopy. The data are indicative of an alignment of this helix parallel to the membrane surface in excellent agreement with the amphipathic character of the foldamer and consistent with previous models explaining the antimicrobial activities of ?-peptides. PMID:22218372

Aisenbrey, Christopher; Pendem, Nagendar; Guichard, Gilles; Bechinger, Burkhard

2012-02-21

140

15N2 Fixation and H2 Evolution by Six Species of Tropical Leguminous Trees 1  

PubMed Central

The C2H4/15N2 and H2/15N2 ratios for six species of tropical leguminous trees are reported. C2H4/15N2 ratios ranged from 2.4 to 4.7; values for the H2/15N2 ratios were between 0.6 and 1.4. Relative efficiency values, based on C2H2 reduction, 15N incorporation, and H2 evolution during 15N incorporation varied between 0.68 and 0.84 for the six species. Overall, approximately 30% of the electron flow through nitrogenase was used for H2 evolution.

van Kessel, Christopher; Roskoski, Joann P.; Wood, Timothy; Montano, Jorge

1983-01-01

141

An sup 15 N NMR method for the characterization of organic sulfur in coal and coal products via iminosulfurane formation  

SciTech Connect

The indirect of organic sulfur by {sup 15}N NMR spectroscopy in the solid state is feasible by facile reactions providing the iminosulfurane structures. Unfortunately, nitrogen chemical shifts appear to be insufficiently sensitive to the nature of the sulfur substituent to be useful for structural studies. Further work is underway to determine the {sup 15}N chemical shifts of iminosulfuranes formed from dibenzothiophene, 4-4{prime}-dimethoxydiphenyl sulfide, and a sulfur-containing, methylated asphaltene to determine the sensitivity of {sup 15}N shifts to a broader variation of aromatic structure. Although double cross-polarization experiments or rotational echo experiments could make use of iminosulfurane formation for detection of carbon in proximity to sulfur, the difficulties in quantitation using these methods are not encouraging for coal product mixtures. 6 refs., 1 fig., 1 tab.

Franz, J.A.; Lamb, C.N.; Linehan, J.C.

1991-09-01

142

Probing the interaction between N(1),N(4)-dibenzylputrescine and tRNA through (15)N NMR: biological implications.  

PubMed

NMR spectroscopy was used to characterize the binding properties of polyamines to Escherichia coli tRNA. The (15)N NMR spectra of three (15)N-enriched N-substituted putrescine derivatives (DMP, DEP and DBP) were recorded in the presence of tRNA, and the spin relaxation times of the nitrogen nuclei were measured. From these data, the activation parameters for the rotational correlation times of the (15)N nuclei were determined. The present data indicate that the nature of the amino substituents does play a relevant role in controlling the polyamine-tRNA interaction. This study also provides a rationale for the in vivo antiproliferative effect of DBP against tumoral cells. PMID:10669796

Fernández, C O; Buldain, G; Samejima, K

2000-02-01

143

New Method for Estimating Bacterial Cell Abundances in Natural Samples by Use of Sublimation  

Microsoft Academic Search

We have developed a new method based on the sublimation of adenine from Escherichia coli to estimate bacterial cell counts in natural samples. To demonstrate this technique, several types of natural samples, including beach sand, seawater, deep-sea sediment, and two soil samples from the Atacama Desert, were heated to a temperature of 500°C for several seconds under reduced pressure. The

Daniel P. Glavin; H. James Cleaves; Michael Schubert; Andrew Aubrey; Jeffrey L. Bada

2004-01-01

144

Resolving isotopic fine structure to detect and quantify natural abundance- and hydrogen/deuterium exchange-derived isotopomers.  

PubMed

Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) is used for analyzing protein dynamics, protein folding/unfolding, and molecular interactions. Until this study, HDX MS experiments employed mass spectral resolving powers that afforded only one peak per nominal mass in a given peptide's isotope distribution, and HDX MS data analysis methods were developed accordingly. A level of complexity that is inherent to HDX MS remained unaddressed, namely, various combinations of natural abundance heavy isotopes and exchanged deuterium shared the same nominal mass and overlapped at previous resolving powers. For example, an A + 2 peak is comprised of (among other isotopomers) a two-(2)H-exchanged/zero-(13)C isotopomer, a one-(2)H-exchanged/one-(13)C isotopomer, and a zero-(2)H-exchanged/two-(13)C isotopomer. Notably, such isotopomers differ slightly in mass as a result of the ?3 mDa mass defect between (2)H and (13)C atoms. Previous HDX MS methods did not resolve these isotopomers, requiring a natural-abundance-only (before HDX or "time zero") spectrum and data processing to remove its contribution. It is demonstrated here that high-resolution mass spectrometry can be used to detect isotopic fine structure, such as in the A + 2 profile example above, deconvolving the isotopomer species resulting from deuterium incorporation. Resolving isotopic fine structure during HDX MS therefore permits direct monitoring of HDX, which can be calculated as the sum of the fractional peak magnitudes of the deuterium-exchanged isotopomers. This obviates both the need for a time zero spectrum as well as data processing to account for natural abundance heavy isotopes, saving instrument and analysis time. PMID:24328359

Liu, Qian; Easterling, Michael L; Agar, Jeffrey N

2014-01-01

145

Probing the local structural environment of calcium by natural-abundance solid-state 43 Ca NMR  

NASA Astrophysics Data System (ADS)

New natural-abundance 43 Ca magic angle spinning (MAS) NMR data measured at high magnetic field ( 14.1 T ) is presented for a range of crystalline calcium-containing binary and ternary inorganic compounds. The combination of high field, moderate MAS (up to 4.5 kHz ), and large sample volume (a 9.5 mm diameter MAS rotor) means that a good signal-to-noise ratio can generally be obtained in a time ( ˜12 h ) that makes 43 Ca NMR a feasible approach for determining information about calcium siting in a wide range of materials of physical interest. This study greatly increases the number of 43 Ca NMR parameters determined for solid materials in the literature, extending reports to local nearest-neighbor coordinations to other than oxygen. These data show that the isotropic chemical shift range is >250 ppm and typically that the quadrupole interaction is <4 MHz . In ternary compounds where Ca is coordinated in the nearest-neighbor shell by only oxygen, the isotropic 43 Ca chemical shift correlates well to the mean Ca-O distance, consistent with the only previous study. In binary compounds the isotropic 43 Ca chemical shift does not appear to be correlated with the mean Ca-X bond length. The extension of natural-abundance 43 Ca MAS NMR studies to amorphous materials are reported by examining sol-gel prepared calcium silicate materials. The data show that in the initial amorphous mixture at lower temperatures (120 350°C) the calcium environment is more like that in the parent calcium nitrate than a silicate, and that further heat treatment causes very significant broadening of the calcium resonance. The implications of this observation for the use of natural-abundance 43 Ca MAS NMR structural studies of amorphous materials are examined.

Lin, Zhongjie; Smith, M. E.; Sowrey, F. E.; Newport, R. J.

2004-06-01

146

ASSESSING ABUNDANCE DISTRIBUTIONS IN NATURAL COMMUNITIES OF ECTOMYCORRHIZAS ALONG AN ENVIRONMENTAL GRADIENT  

EPA Science Inventory

Alpha diversity indices often fail to distinguish between natural populations that a more detailed investigation of the distribution of ramets among types would show are quite different. We studied the effectiveness of applying SHE analyses to morphotype classifications of ectom...

147

Apelin, the natural ligand of the orphan receptor APJ, is abundantly secreted in the colostrum  

Microsoft Academic Search

By using a strategy that we have developed to search for the ligands of orphan seven-transmembrane-domain receptors [S. Hinuma et al., Nature 393 (1998) 272–276], we have recently identified a natural ligand, apelin, for the orphan 7TMR, APJ [K. Tatemoto et al., Biochem. Biophys. Res. Commun. 251 (1998) 471–476]. In this paper, we isolated rat and mouse apelin cDNAs, and

Yugo Habata; Ryo Fujii; Masaki Hosoya; Shoji Fukusumi; Yuji Kawamata; Shuji Hinuma; Chieko Kitada; Naoki Nishizawa; Shinji Murosaki; Tsutomu Kurokawa; Haruo Onda; Kazuhiko Tatemoto; Masahiko Fujino

1999-01-01

148

Intercontinental Differences in the Abundance of Solenopsis Fire Ants (Hymenoptera: Formicidae): Escape from Natural Enemies?  

Microsoft Academic Search

Environ. Entomol. 26(2): 373-384 (1997) ABSTRACT The absence of natural enemies often allows exotic pests to reach densities that are much higher than normally occur in their native habitats. When SoLnopsis fire ants were introduced into the United States, their numerous natural enemies were left behind in South America. To compare intercontinental fire ant densities, we selected 13 areas in

SANFORD D. PORTER; DAVID F. WILLIAMS; RICHARD S. PATTERSON; HAROLD G. FOWLERl

149

Paleoenvironmental implications of taxonomic variation among ??15N values of chloropigments  

USGS Publications Warehouse

Natural variations in the ratios of nitrogen isotopes in biomass reflect variations in nutrient sources utilized for growth. In order to use ??15N values of chloropigments of photosynthetic organisms to determine the corresponding ??15N values of biomass - and by extension, surface waters - the isotopic offset between chlorophyll and biomass must be constrained. Here we examine this offset in various geologically-relevant taxa, grown using nutrient sources that may approximate ocean conditions at different times in Earth's history. Phytoplankton in this study include cyanobacteria (diazotrophic and non-diazotrophic), eukaryotic algae (red and green), and anoxygenic photosynthetic bacteria (Proteobacteria), as well as environmental samples from sulfidic lake water. Cultures were grown using N2, NO3-, and NH4+ as nitrogen sources, and were examined under different light regimes and growth conditions. We find surprisingly high variability in the isotopic difference (??15Nbiomass-??15Nchloropigment) for prokaryotes, with average values for species ranging from -12.2??? to +11.7???. We define this difference as ??por, a term that encompasses diagenetic porphyrins and chlorins, as well as chlorophyll. Negative values of ??por reflect chloropigments that are 15N-enriched relative to biomass. Notably, this enrichment appears to occur only in cyanobacteria. The average value of ??por for freshwater cyanobacterial species is -9.8??1.8???, while for marine cyanobacteria it is -0.9??1.3???. These isotopic effects group environmentally but not phylogenetically, e.g., ??por values for freshwater Chroococcales resemble those of freshwater Nostocales but differ from those of marine Chroococcales. Our measured values of ??por for eukaryotic algae (range=4.7-8.7???) are similar to previous reports for pure cultures. For all taxa studied, values of ??por do not depend on the type of nitrogen substrate used for growth. The observed environmental control of ??por suggests that values of ??por could be useful for determining the fractional burial of eukaryotic vs. cyanobacterial organic matter in the sedimentary record. ?? 2011 Elsevier Ltd.

Higgins, M. B.; Wolfe-Simon, F.; Robinson, R. S.; Qin, Y.; Saito, M. A.; Pearson, A.

2011-01-01

150

A theory for 15 N\\/ 14 N fractionation in nitrate-grown vascular plants  

Microsoft Academic Search

.   We present a theory describing how the ?15N values of the nitrogen (N) pools in a vascular plant depend on that of its source N (nitrate), on 15N\\/14N fractionations during N assimilation, and on N transport within and N loss from the plant. The theory allows measured ?15N values to be interpreted in terms of physiological processes. The ?15N

David Robinson; L. L. Handley; C. M. Scrimgeour

1998-01-01

151

Trends in Fishing Mortality Rate along with Errors in Natural Mortality Rate can cause Spurious Time Trends in Fish Stock Abundances Estimated by Virtual Population Analysis (VPA)  

Microsoft Academic Search

Many researchers have reported biases in estimates of fish abundance reconstructed by virtual population analysis (VPAI. We document that VPA can produce changing levels of bias through time, thereby creating spurious time trends in recruitment and stock biomass estimates. We generated catch data from empirically based simulations oi nine fish populations. estimated abundances using VPA with a deliberately mis-specified natural

Michael F. Lapointe; Randall M. Peterman; Alec D. MacCall

1989-01-01

152

Avifauna of Sierra Nevada Network Parks Assessing Distribution, Abundance, Stressors, and Conservation Opportunities for 145 Bird Species (Appendix A - Species Accounts), Natural Resource Report.  

National Technical Information Service (NTIS)

To inform and support the Sierra Nevada Network's long-term bird monitoring program and the Sequoia and Kings Canyon Natural Resource Condition Assessment, we assessed distribution, abundance, ecological stressors, and conservation opportunities for 145 b...

M. L. Bond P. Pyle R. B. Siegel Z. L. Steel

2012-01-01

153

Natural abundance solid-state 67Zn NMR characterization of microporous zinc phosphites and zinc phosphates at ultrahigh magnetic field.  

PubMed

Zinc-phosphite and -phosphate based microporous materials are crystalline open framework materials with potential industrial applications. Although (31)P MAS NMR has been used for characterization of these materials, the local environments around zinc centres have never been directly probed by solid-state NMR due to the many unfavourable NMR characteristics of (67)Zn. In this work, we have characterized the local structure around the Zn centres in several representative microporous zinc phosphites and zinc phosphates by acquiring natural abundance (67)Zn solid-state NMR spectra at ultrahigh magnetic field of 21.1 T. The observed line-shapes are mainly determined by the second order quadrupolar interaction. The NMR tensor parameters were extracted from the spectra and are related to the local geometry around the Zn centre. Computational study of the electric field gradient (EFG) tensor at Zn was performed using hybrid density functional theory (DFT) calculations at B3LYP level of theory on model clusters. The calculations using Projector Augmented-Wave (PAW) method were also carried out with the CASTEP code wherever it was possible. The work has shown that it is possible to study Zn environments in porous materials which often have very low Zn concentration by natural abundance (67)Zn SSNMR at very high magnetic fields. PMID:21850324

Sutrisno, Andre; Liu, Li; Xu, Jun; Huang, Yining

2011-10-01

154

Dynamic nuclear polarization NMR enables the analysis of sn-Beta zeolite prepared with natural abundance (119)sn precursors.  

PubMed

The catalytic activity of tin-containing zeolites, such as Sn-Beta, is critically dependent on the successful incorporation of the tin metal center into the zeolite framework. However, synchrotron-based techniques or solid-state nuclear magnetic resonance (ssNMR) of samples enriched with (119)Sn isotopes are the only reliable methods to verify framework incorporation. This work demonstrates, for the first time, the use of dynamic nuclear polarization (DNP) NMR for characterizing zeolites containing ?2 wt % of natural abundance Sn without the need for (119)Sn isotopic enrichment. The biradicals TOTAPOL, bTbK, bCTbK, and SPIROPOL functioned effectively as polarizing sources, and the solvent enabled proper transfer of spin polarization from the radical's unpaired electrons to the target nuclei. Using bCTbK led to an enhancement (?) of 75, allowing the characterization of natural-abundance (119)Sn-Beta with excellent signal-to-noise ratios in <24 h. Without DNP, no (119)Sn resonances were detected after 10 days of continuous analysis. PMID:24697321

Gunther, William R; Michaelis, Vladimir K; Caporini, Marc A; Griffin, Robert G; Román-Leshkov, Yuriy

2014-04-30

155

Detection of 15NNH+ in L1544: non-LTE modelling of dyazenilium hyperfine line emission and accurate 14N/15N values  

NASA Astrophysics Data System (ADS)

Context. Samples of pristine solar system material found in meteorites and interplanetary dust particles are highly enriched in 15N. Conspicuous nitrogen isotopic anomalies have also been measured in comets, and the 14N/15N abundance ratio of the Earth is itself higher than the recognised presolar value by almost a factor of two. Low-temperature ion/molecule reactions in the proto-solar nebula have been repeatedly indicated as being responsible for these 15N-enhancements. Aims: We have searched for 15N variants of the N2H+ ion in L1544, a prototypical starless cloud core that is one of the best candidate sources for detection owing to its low central core temperature and high CO depletion. The goal is to evaluate accurate and reliable 14N/15N ratio values for this species in the interstellar gas. Methods: A deep integration of the 15NNH+(1-0) line at 90.4 GHz was obtained with the IRAM 30 m telescope. Non-LTE radiative transfer modelling was performed on the J = 1-0 emissions of the parent and 15N-containing dyazenilium ions, using a Bonnor-Ebert sphere as a model for the source. Results: A high-quality fit of the N2H+(1-0) hyperfine spectrum has allowed us to derive a revised value of the N2H+ column density in L1544. Analysis of the observed N15NH+ and 15NNH+ spectra yielded an abundance ratio N(N15NH+)/N(15NNH+) = 1.1 ± 0.3. The obtained 14N/15N isotopic ratio is ~1000 ± 200, suggestive of a sizeable 15N depletion in this molecular ion. Such a result is not consistent with the prediction of the current nitrogen chemical models. Conclusions: Since chemical models predict high 15N fractionation of N2H+, we suggest that 15N14N, or 15N in some other molecular form, tends to deplete onto dust grains. Based on observations carried out with the IRAM 30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).Full Tables B.1-B.6 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A109

Bizzocchi, L.; Caselli, P.; Leonardo, E.; Dore, L.

2013-07-01

156

Natural N-terminal fragments of brain abundant myristoylated protein BASP1.  

PubMed

BASP1 (also known as CAP-23 and NAP-22) is a novel myristoylated calmodulin-binding protein, abundant in nerve terminals. It is considered as a signal protein participating in neurite outgrowth and synaptic plasticity. BASP1 is also present in significant amounts in kidney, testis, and lymphoid tissues. In this study, we show that BASP1 is accompanied by at least six BASP1 immunologically related proteins (BIRPs), which are present in all animal species studied (rat, bovine, human, chicken). BIRPs have lower molecular masses than that of BASP1. Similarly to BASP1, they are myristoylated. Peptide mapping and partial sequencing have shown that BIRPs represent a set of BASP1 N-terminal fragments devoid of C-terminal parts of different length. In a definite species, the same set of BASP1 fragments is present in both brain and other tissues. The sum amount of the fragments is about 50% of the BASP1 amount in a tissue. Obligatory accompanying of BASP1 by a set of specific fragments indicates that these fragments are of physiological significance. PMID:12829256

Zakharov, Vladislav V; Capony, Jean-Paul; Derancourt, Jean; Kropolova, Ekaterina S; Novitskaya, Vera A; Bogdanova, Marina N; Mosevitsky, Mark I

2003-06-20

157

Effect of the Squid Host on the Abundance and Distribution of Symbiotic Vibrio fischeri in Nature  

PubMed Central

Euprymna scolopes, a Hawaiian species of bioluminescent squid, harbors Vibrio fischeri as its specific light organ symbiont. The population of symbionts grew inside the adult light organ with an average doubling time of about 5 h, which produced an excess of cells that were expelled into the surrounding seawater on a diurnal basis at the beginning of each period of daylight. These symbionts, when expelled into the ambient seawater, maintain or slightly increase their numbers for at least 24 h. Hence, locations inhabited by their hosts periodically receive a daily input of symbiotic V. fischeri cells and, as a result, become significantly enriched with these bacteria. As estimated by hybridization with a species-specific luxA gene probe, the typical number of V. fischeri CFU, both in the water column and in the sediments of E. scolopes habitats, was as much as 24 to 30 times that in similar locations where squids were not observed. In addition, the number of symbiotic V. fischeri CFU in seawater samples that were collected along a transect through Kaneohe Bay, Hawaii, decreased as a function of the distance from a location inhabited by E. scolopes. These findings constitute evidence for the first recognized instance of the abundance and distribution of a marine bacterium being driven primarily by its symbiotic association with an animal host.

Lee, Kyu-Ho; Ruby, Edward G.

1994-01-01

158

New method for estimating bacterial cell abundances in natural samples by use of sublimation  

NASA Technical Reports Server (NTRS)

We have developed a new method based on the sublimation of adenine from Escherichia coli to estimate bacterial cell counts in natural samples. To demonstrate this technique, several types of natural samples, including beach sand, seawater, deep-sea sediment, and two soil samples from the Atacama Desert, were heated to a temperature of 500 degrees C for several seconds under reduced pressure. The sublimate was collected on a cold finger, and the amount of adenine released from the samples was then determined by high-performance liquid chromatography with UV absorbance detection. Based on the total amount of adenine recovered from DNA and RNA in these samples, we estimated bacterial cell counts ranging from approximately 10(5) to 10(9) E. coli cell equivalents per gram. For most of these samples, the sublimation-based cell counts were in agreement with total bacterial counts obtained by traditional DAPI (4,6-diamidino-2-phenylindole) staining.

Glavin, Daniel P.; Cleaves, H. James; Schubert, Michael; Aubrey, Andrew; Bada, Jeffrey L.

2004-01-01

159

Linking nitrogen dynamics to climate variability off central California: a 51 year record based on 15N/ 14N in CalCOFI zooplankton  

NASA Astrophysics Data System (ADS)

Long-term variability in zooplankton 15N/ 14N was investigated in two species of calanoid copepods ( Calanus pacificus and Eucalanus californicus) and two chaetognaths ( Sagitta bierii and Sagitta euneritica) sampled in the spring of selected years from 1951 to 2001 off the central California coast. No statistically significant trend in 15N/ 14N was detected for any of the four species, with isotopic ratios in 2001 resembling those in copepods and chaetognaths sampled five decades earlier. Zooplankton body lengths also showed no long-term trends. With respect to proposed regime shifts in this region, heterogeneity in 15N/ 14N was detected only for S. bierii when comparing the periods 1951-1975, 1978-1998, and 1999-2001. In this species the 15N/ 14N in the most recent, brief period (1999-2001) averaged slightly lower than in the previous period. Three of the four species ( C. pacificus, S. bierii, and S. euneritica) showed significant increases in 15N/ 14N during major El Niños. El Niño-related enrichment in 15N could arise as a consequence of increased nitrate demand:supply at the base of the food web or advection of 15N-enriched nitrate from more southerly waters. While a range of physical and climate indices were evaluated, anomalies of 15N/ 14N from the long-term mean were found to be significantly related only to: (i) the Southern Oscillation Index in the case of both chaetognath species, (ii) a regional surface water temperature record ( S. bierii only), (iii) an index of wind-driven coastal upwelling for the surface-dwelling C. pacificus, and (iv) variability in the Pacific Decadal Oscillation for the somewhat deeper-dwelling E. californicus. The relationships among each species' 15N/ 14N averaged over the total sampling period was: E. californicus?C. pacificus?S. euneritica < S. bierii, consistent with trophic 15N biomagnification and the predatory nature of Sagitta.

Rau, Greg H.; Ohman, Mark D.; Pierrot-Bults, Annelies

2003-08-01

160

/sup 15/N tracer kinetic studies on the validity of various /sup 15/N tracer substances for determining whole-body protein parameters in very small preterm infants  

SciTech Connect

Reliable /sup 15/N tracer substances for tracer kinetic determination of whole-body protein parameters in very small preterm infants are still a matter of intensive research, especially after some doubts have been raised about the validity of (/sup 15/N)glycine, a commonly used /sup 15/N tracer. Protein turnover, synthesis, breakdown, and further protein metabolism data were determined by a paired comparison in four preterm infants. Their post-conceptual age was 32.2 +/- 0.8 weeks, and their body weight was 1670 +/- 181 g. Tracer substances applied in this study were a (/sup 15/N)amino acid mixture (Ia) and (/sup 15/N)glycine (Ib). In a second group of three infants with a post conceptual age of /sup 15/N-labeled 32.0 +/- 1.0 weeks and a body weight of 1,907 +/- 137 g, yeast protein hydrolysate (II) was used as a tracer substance. A three-pool model was employed for the analysis of the data. This model takes into account renal and fecal /sup 15/N losses after a single /sup 15/N pulse. Protein turnovers were as follows: 11.9 +/- 3.1 g kg-1 d-1 (Ia), 16.2 +/- 2.5 g kg-1 d-1 (Ib), and 10.8 +/- 3.0 g kg-1 d-1 (II). We were able to demonstrate an overestimation of the protein turnover when Ib was used. There was an expected correspondence in the results obtained from Ia and II. The /sup 15/N-labeled yeast protein hydrolysate is a relatively cheap tracer that allows reliable determination of whole-body protein parameters in very small preterm infants.

Plath, C.; Heine, W.; Wutzke, K.D.; Krienke, L.; Toewe, J.M.; Massute, G.; Windischmann, C.

1987-05-01

161

The metabolic effect of resistant starch and yoghurt on the renal and faecal nitrogen and ammonia excretion in humans as measured by lactose-[(15)N2]ureide.  

PubMed

Resistant starch (RS) and Lactobacillus acidophilus yoghurt (LC1) were supplemented simultaneously in healthy adults to evaluate the effect on the urinary and faecal nitrogen and ammonia excretion by means of lactose-[(15)N2]ureide ((15)N-LU) degradation. Nineteen subjects received a regular daily diet either without or with supplementation of an RS-LC1-mixture composed of fibre of potatoes (RS type 1), wrinkle pea starch (RS type 2), and LC1 over a 20-day period in randomised order. Thereafter, (15)N-LU was administered together with breakfast. Urine and faeces were collected over a period of 48 and 72 h, respectively. The (15)N abundances were measured by isotope ratio mass spectrometry. The intake of the pre- and probiotic mixture composed of RS of type 1, type 2 and of LC1 significantly lowered the colonic generation and the renal excretion of toxic (15)NH3 and functioned as an ammonia shift from urinary to faecal (15)N excretion when using (15)N-LU as a xenobiotic marker. PMID:23937067

Wutzke, Klaus D; Scholübbers, Debora

2013-01-01

162

A New Method for Estimating Bacterial Abundances in Natural Samples using Sublimation  

NASA Technical Reports Server (NTRS)

We have developed a new method based on the sublimation of adenine from Escherichia coli to estimate bacterial cell counts in natural samples. To demonstrate this technique, several types of natural samples including beach sand, seawater, deep-sea sediment, and two soil samples from the Atacama Desert were heated to a temperature of 500 C for several seconds under reduced pressure. The sublimate was collected on a cold finger and the amount of adenine released from the samples then determined by high performance liquid chromatography (HPLC) with UV absorbance detection. Based on the total amount of adenine recovered from DNA and RNA in these samples, we estimated bacterial cell counts ranging from approx. l0(exp 5) to l0(exp 9) E. coli cell equivalents per gram. For most of these samples, the sublimation based cell counts were in agreement with total bacterial counts obtained by traditional DAPI staining. The simplicity and robustness of the sublimation technique compared to the DAPI staining method makes this approach particularly attractive for use by spacecraft instrumentation. NASA is currently planning to send a lander to Mars in 2009 in order to assess whether or not organic compounds, especially those that might be associated with life, are present in Martian surface samples. Based on our analyses of the Atacama Desert soil samples, several million bacterial cells per gam of Martian soil should be detectable using this sublimation technique.

Glavin, Daniel P.; Cleaves, H. James; Schubert, Michael; Aubrey, Andrew; Bada, Jeffrey L.

2004-01-01

163

Apelin, the natural ligand of the orphan receptor APJ, is abundantly secreted in the colostrum.  

PubMed

By using a strategy that we have developed to search for the ligands of orphan seven-transmembrane-domain receptors [S. Hinuma et al., Nature 393 (1998) 272-276], we have recently identified a natural ligand, apelin, for the orphan 7TMR, APJ [K. Tatemoto et al., Biochem. Biophys. Res. Commun. 251 (1998) 471-476]. In this paper, we isolated rat and mouse apelin cDNAs, and analyzed the tissue distribution of apelin mRNA in rats. Although apelin mRNA was widely detected in a variety of tissues, the highest expression of apelin mRNA was detected in the mammary gland of pregnant rats. In the mammary gland, biologically active apelin and its mRNA considerably increased during pregnancy and lactation, and reached a maximal level around parturition. Moreover, a large amount of apelin (14-93 pmol/ml) was found to be secreted in the bovine colostrum, and it was still detectable even in commercial bovine milk. Since apelin partially suppressed cytokine production by mouse spleen cells in response to T cell receptor/CD3 cross-linking, the oral intake of apelin in the colostrum and milk might modulate immune responses in neonates. PMID:10525157

Habata, Y; Fujii, R; Hosoya, M; Fukusumi, S; Kawamata, Y; Hinuma, S; Kitada, C; Nishizawa, N; Murosaki, S; Kurokawa, T; Onda, H; Tatemoto, K; Fujino, M

1999-10-13

164

Nature and abundance of organic radicals in natural organic matter: effect of pH and irradiation.  

PubMed

Dissolved natural organic matter (NOM) plays an essential role in freshwater geochemical and biochemical processes. A major property, its redox behavior, can be attributed to the chinone building blocks, which can form stable radicals. However, electron paramagnetic resonance (EPR) data indicating free radicals on solid NOM are sparse. Here we present EPR spectra of 23 NOM from European surface waters isolated by reverse osmosis. The organic radical concentrations of NOM ranged from 5 x 10(15) to 1.84 x 10(17) spins g(-1), and g values ranged from 2.0031 to 2.0045. Number and type of organic radicals in solid NOM are significantly influenced by the pH of raw water. EPR experiments indicate the presence of semiquinone-type radicals in coexistence with carbon-centered "aromatic" radicals, with the semiquinone-type radicals dominating at alkaline pH. Basically these processes are reversible. Organic radical concentrations in NOM adjusted to pH 6.5 before freeze-drying correlate with iron and aluminum contents. UV- and VIS-irradiation of solid NOM can lead to more than a 10-fold increase of the concentration of organic radicals. These radicals were long-lived and had the same g value as the original radical. Similar effects were not observed with isolated humic and fulvic acids, demonstrating the limited reflection of environmental properties of organic carbon by the classical isolation procedure. PMID:17051776

Paul, Andrea; Stösser, Reinhard; Zehl, Andrea; Zwirnmann, Elke; Vogt, Rolf D; Steinberg, Christian E W

2006-10-01

165

Determination of 15N/14N and 13C/12C in Solid and Aqueous Cyanides  

USGS Publications Warehouse

The stable isotopic compositions of nitrogen and carbon in cyanide compounds can be determined by combusting aliquots in sealed tubes to form N2 gas and CO2 gas and analyzing the gases by mass spectrometry. Free cyanide (CN-aq + HCNaq) in simple solutions can also be analyzed by first precipitating the cyanide as copper(II) ferrocyanide and then combusting the precipitate. Reproducibility is ??0.5??? or better for both ??15N and ??13C. If empirical corrections are made on the basis of carbon yields, the reproducibility of ??13C can be improved to ??0.2???. The analytical methods described herein are sufficiently accurate and precise to apply stable isotope techniques to problems of cyanide degradation in natural waters and industrial process solutions.

Johnson, C. A.

1996-01-01

166

Test for the shell-model-Weinberg treatment of the reaction 15 N( n,n? ) 15 N * with a separable interaction  

Microsoft Academic Search

A modification of Weinberg's method in connection with the Born approximation was first employed by Ebenhöhet al. to describe the reaction15N(n, n')15N* using a delta-force as residual interaction. This method is now applied to the same reaction but using a surface-delta-interaction. For this separable interaction also the exact solution of the problem is presented. We were not interested in adjusting

Bertram Pöpel; Gerhard Schütte

1970-01-01

167

Stabilization dynamics of root versus needle-derived 13C and 15N during 10 years in a temperate forest soil.  

NASA Astrophysics Data System (ADS)

Belowground plant carbon (C) allocation as fine roots can result in greater retention of C in soils compared with aboveground litter in temperate forest ecosystems. However, much of our understanding of the fate of fine root C and nitrogen (N) in soils comes from short-term studies, often lasting only a few months to a few years. In 2011, we concluded a 10-year field study that compared the fate of dual-labeled (13C/15N) Ponderosa pine fine roots (<2 mm diameter) with needles in a temperate forest soil of the Sierra Nevada, CA, USA. The 13C- and 15N-labeled fine roots or needles were added to mesocosms at two soil depths (top of O or A horizon) to compare C and N stabilization in mineral versus organic soil horizons. We will present data on retention of litter C and N in soil after 0.5, 1.5, 5 and 10 years in situ. For soil samples recovered after 5 years, litter-derived C and N recovered in the mineral soil was partitioned into several operationally-defined physical and chemical soil organic matter (SOM) fractions, which were also characterized by natural abundance 14C. In addition, we compared two fractionation methods (i.e., with and without occluded light fraction isolation) on the partitioning of litter-derived C and N in mineral soil. After 5 years in situ the retention of fine root C in soil (59.9±3.8%) was significantly greater than that of added needle C (38.4±2.0%); however the depth of litter placement in the soil did not affect total litter C or N recovery. Our results provide a direct, decade-scale measure of stabilization of above- and belowground plant inputs to soil, including a portrait of the dominant stabilization mechanisms.

Bird, J. A.; Hatton, P. J.; Castanha, C.; Torn, M. S.

2012-12-01

168

Effects of weed cover composition on insect pest and natural enemy abundance in a field of Dracaena marginata (Asparagales: Asparagaceae) in Costa Rica.  

PubMed

Weeds and their influence on pest and natural enemy populations were studied on a commercial ornamental farm during 2009 in the Atlantic Zone of Costa Rica. A baseline survey of the entire production plot was conducted in February, along a 5 by 5 m grid to characterize and map initial weed communities of plants, cicadellids, katydids, and armored scales. In total, 50 plant species from 21 families were found. Seven weed treatments were established to determine how weed manipulations would affect communities of our targeted pests and natural enemies. These treatments were selected based on reported effects of specific weed cover on herbivorous insects and natural enemies, or by their use by growers as a cover crop. Treatments ranged from weed-free to being completely covered with endemic species of weeds. Although some weed treatments changed pest abundances, responses differed among arthropod pests, with the strongest effects observed for Caldwelliola and Empoasca leafhoppers. Removal of all weeds increased the abundance of Empoasca, whereas leaving mostly cyperacaeous weeds increased the abundance of Caldwelliola. Weed manipulations had no effect on the abundance of katydid and scale populations. No weed treatment reduced the abundance of all three of the target pests. Differential responses of the two leafhopper species to the same weed treatments support hypotheses, suggesting that noncrop plants can alter the abundance of pests through their effects on arthropod host finding and acceptance, as well as their impacts on natural enemies. PMID:24517852

Sadof, Clifford S; Linkimer, Mildred; Hidalgo, Eduardo; Casanoves, Fernando; Gibson, Kevin; Benjamin, Tamara J

2014-04-01

169

Sources of material for 'loess' deposits at 15°N in North Africa  

NASA Astrophysics Data System (ADS)

Africa is not a loess-rich continent. Lacking are the large expanses of glacial terrain and the high cold mountain regions, which would have provided the material and processes for loess deposits. African geomorphology and climatic history did not favour the formation of major loess deposits. However, within the African setting there are situations which could lead to particle formation and loess deposition. Loess deposits are made from 'large' dust (i.e. particles around 30µm). Small dust (around 3µm) is generated in large amounts in Africa, and distributed over large distances. Large dust is not generated in significant amounts in Africa, and this accounts for the relative lack of loess deposits. It is a relative lack; examination of the map of loess distribution in the World by Scheidig 1934 (still the best world loess map) shows some possible loess in Africa. In particular there is a band across the continent at around 15°N. We propose some possible sources for this material, and fit these sources into a recently revised deterministic model of loess deposit formation. And look at some exotic but possible indicators of the loessic nature of the 15°N band. Three possible material sources are: (1). The Fonta-Djalon highlands to the west of the loess band, (2). The Bodélé Depression, towards the centre of the loess band, and (3). The Ethiopian highlands to the east. There is a convenient river associated with the loess band; the Niger rises in the Fonta-Djalon region and carries material through the loess zone. The catchment of the Niger is well placed to receive large dust material from the Bodélé depression. Most Bodélé material is small dust carried away in high suspension but small amounts of large dust could be transported to the Niger catchment. Material from the Ethiopian highlands makes up the Nile silt but again some could be transported to the west to contribute to the loess band- which is a modest loess deposit. The deposit can be examined with respect to the deterministic model of loess deposit formation which sets out four event aspects which must be accommodated. PTDC: provenance (of material), transportation, deposition and change- all need to be considered when loess deposit genesis is examined. In the case of the 15°N loess the P actions are speculative, and probably not very effective. In fact the deposits they deliver, as mapped by Scheidig, still have to be established as genuine loess. There are indicators of loessic nature; one is that they are favoured by tunnel nesting birds, in particular bee-eaters. Merops apiaster (the European bee-eater) travels large distances to nest in the European loess. The bee-eater nesting zones map nicely on to European loess distribution. In the 15°N zone there is a concentration of nesting activity by the Northern Carmine bee-eater (Merops nubicus) and we take this as an indicator of ground nature.

McLaren, Sue; Smalley, Ian; O'Hara-Dhand, Ken

2014-05-01

170

Nutrient regime shift in the western North Atlantic indicated by compound-specific ?15N of deep-sea gorgonian corals  

PubMed Central

Despite the importance of the nitrogen (N) cycle on marine productivity, little is known about variability in N sources and cycling in the ocean in relation to natural and anthropogenic climate change. Beyond the last few decades of scientific observation, knowledge depends largely on proxy records derived from nitrogen stable isotopes (?15N) preserved in sediments and other bioarchives. Traditional bulk ?15N measurements, however, represent the combined influence of N source and subsequent trophic transfers, often confounding environmental interpretation. Recently, compound-specific analysis of individual amino acids (?15N-AA) has been shown as a means to deconvolve trophic level versus N source effects on the ?15N variability of bulk organic matter. Here, we demonstrate the first use of ?15N-AA in a paleoceanographic study, through analysis of annually secreted growth rings preserved in the organic endoskeletons of deep-sea gorgonian corals. In the Northwest Atlantic off Nova Scotia, coral ?15N is correlated with increasing presence of subtropical versus subpolar slope waters over the twentieth century. By using the new ?15N-AA approach to control for variable trophic processing, we are able to interpret coral bulk ?15N values as a proxy for nitrate source and, hence, slope water source partitioning. We conclude that the persistence of the warm, nutrient-rich regime since the early 1970s is largely unique in the context of the last approximately 1,800 yr. This evidence suggests that nutrient variability in this region is coordinated with recent changes in global climate and underscores the broad potential of ?15N-AA for paleoceanographic studies of the marine N cycle.

Sherwood, Owen A.; Lehmann, Moritz F.; Schubert, Carsten J.; Scott, David B.; McCarthy, Matthew D.

2011-01-01

171

15 N 2 Incorporation and metabolism in the lichen Peltigera aphthosa Willd  

Microsoft Academic Search

The Nostoc in the cephalodia of the lichen Peltigera aphthosa Willd. fixed 15N2 and the bulk of the nitrogen fixed was continuously transferred from it to its eukaryotic partners (a fungus and a green alga, Coccomyxa sp.). Kinetic studies carried out over the first 30 min, after exposure of isolated cephalodia to 15N2, showed that highest initial 15N2-labelling was into

A. N. Rai; P. Rowell; W. D. P. Stewart

1981-01-01

172

Sources of ?15N variability in sinking particulate nitrogen in the Cariaco Basin, Venezuela  

NASA Astrophysics Data System (ADS)

Ten years of monthly observations of the ?15N of sinking particulate nitrogen (?15N-PN (in ‰ versus atmospheric N2)=[(15N/14N)sample/(15N/14N)standard)-1]1000) in the Cariaco Basin, Venezuela, confirm that the basin's bottom sediments store information about nitrogen dynamics related to seasonal and interannual variability in regional surface ocean processes. During the upwelling period of the southern Caribbean Sea (February-April), the ?15N-PN is similar to that of the thermocline nitrate (˜3.5‰). This nitrate is imported into the Cariaco Basin with Subtropical Underwater (SUW), which wells up near the coast. Thus, particles generated by phytoplankton photosynthesis during this productive period bear a sub-tropical North Atlantic isotopic imprint of N2 fixation (low compared to the global average of nitrate ?15N?5‰). During the non-upwelling period when surface waters are stratified (September-November), the ?15N-PN is also 3.5-4.0‰, and reflects a mixture of local N2 fixation within the mixed layer, inputs of terrigenous organic matter and SUW nitrate consumption by phytoplankton below the mixed layer, which most likely exerts the strongest control on the ?15N-PN signal during this time. In the transition periods of May-July and December-January, the ?15N-PN increases to 4.5-6.5‰. This coincides with maxima of continental material fluxes (terrestrial PON ?15N is >6‰) into the Cariaco Basin. The ?15N signal in the sediments of the Cariaco Basin thus provides information about the relative strength of the local coastal upwelling, the relative input of continental material via river runoff, and local N2 fixation. The findings contribute to interpretations of the basin's paleoclimatic nitrogen cycle variations based on observations of the sedimentary ?15N record at this location.

Montes, Enrique; Thunell, Robert; Muller-Karger, Frank E.; Lorenzoni, Laura; Tappa, Eric; Troccoli, Luis; Astor, Yrene; Varela, Ramón

2013-09-01

173

Binding of thiocyanate to lactoperoxidase: 1H and 15N nuclear magnetic resonance studies  

SciTech Connect

The binding of thiocyanate to lactoperoxidase (LPO) has been investigated by 1H and 15N NMR spectroscopy. 1H NMR of LPO shows that the major broad heme methyl proton resonance at about 61 ppm is shifted upfield by addition of the thiocyanate, indicating binding of the thiocyanate to the enzyme. The pH dependence of line width of 15N resonance of SC15N- in the presence of the enzyme has revealed that the binding of the thiocyanate to the enzyme is facilitated by protonation of an ionizable group (with pKa of 6.4), which is presumably distal histidine. Dissociation constants (KD) of SC15N-/LPO, SC15N-/LPO/I-, and SC15N-/LPO/CN- equilibria have been determined by 15N T1 measurements and found to be 90 +/- 5, 173 +/- 20, and 83 +/- 6 mM, respectively. On the basis of these values of KD, it is suggested that the iodide ion inhibits the binding of the thiocyanate but cyanide ion does not. The thiocyanate is shown to bind at the same site of LPO as iodide does, but the binding is considerably weaker and is away from the ferric ion. The distance of 15N of the bound thiocyanate ion from the iron is determined to be 7.2 +/- 0.2 A from the 15N T1 measurements.

Modi, S.; Behere, D.V.; Mitra, S. (Tata Institute of Fundamental Research, Bombay (India))

1989-05-30

174

Measurement of 15 N relaxation in the detergent-solubilized tetrameric KcsA potassium channel  

Microsoft Academic Search

A set of TROSY-HNCO (tHNCO)-based 3D experiments is presented for measuring 15N relaxation parameters in large, membrane-associated proteins, characterized by slow tumbling times and significant spectral\\u000a overlap. Measurement of backbone 15N R\\u000a 1, R\\u000a 1?, 15N–{1H} NOE, and 15N CSA\\/dipolar cross correlation is demonstrated and applied to study the dynamic behavior of the homotetrameric KcsA potassium\\u000a channel in SDS micelles

Jordan H. Chill; John M. Louis; James L. Baber; Ad Bax

2006-01-01

175

Nutrient Status and ?15N Values in Leaves and Soils: A Cross-Biome Comparison  

NASA Astrophysics Data System (ADS)

Stable nitrogen (N) isotope ratios (?15N) are often assumed to provide an integrated measure of multiple nitrogen cycling processes. For instance, shifts in the bioavailability of soil N forms are thought to alter plant ?15N values. Demonstrating this relationship is important as ecosystems undergo anthropogenic disturbances. We evaluated patterns and implied mechanisms of the N cycle using ecosystem ?15N values from 16 plots in boreal black spruce (Picea mariana) forest and lowland wet tropical forest. Fertilizer N and phosphorus (P) was applied annually for five and 11 years prior to measurement of ecosystem ?15N values. Full sun canopy foliage and soil extractable nitrate, ammonium, and dissolved organic N (DON) were sampled in fertilized and control plots and analyzed for ?15N. In boreal forest, N fertilization reduced DON concentrations and caused a depletion of ?15N in foliage and fungal sporocarps. Of four species occurring in all plots in the tropical forest, one (Alseis blackiana) had increased foliar ?15N values following N fertilization, one (Tetragastris panamensis) had increased foliar ?15N values following P fertilization, and one (Oenocarpus mapora) had increased foliar ?15N following N+P fertilization. Surprisingly, soil nitrate in the boreal forest became substantially 15N-enriched under P fertilization, whereas nitrate in the tropical forest soil was enriched only under N or N+P fertilization. Collectively, nitrate enrichment is likely due to enhanced rates of soil denitrification as evidenced by elevated resin extractable soil nitrate concentrations and close correlations between ?15N and ?18O values. On average, foliar ?15N in tropical trees corresponded well with ?15N in soil nitrate in control and P fertilized plots, but was 2-3% more enriched than DON under N and N+P fertilization. In boreal forests, N and N+P fertilization increased foliar N concentration and ?15N values indicating substantial use of applied fertilizer. Taken together, these results suggest that altering soil fertility changes soil N fractionation pathways and resulting foliar ?15N values, although the direction and magnitude of the changes varies by biome and species, notwithstanding soil types. The utility of ?15N measurements for detecting changes in the N cycle will be discussed.

Mayor, J. R.; Schuur, E. A.; Turner, B. L.; Wright, S. J.

2011-12-01

176

Female offspring desertion and male-only care increase with natural and experimental increase in food abundance  

PubMed Central

In species with biparental care, one parent may escape the costs of parental care by deserting and leaving the partner to care for the offspring alone. A number of theoretical papers have suggested a link between uniparental offspring desertion and ecological factors, but empirical evidence is scarce. We investigated the relationship between uniparental desertion and food abundance in a natural population of Tengmalm's owl Aegolius funereus, both by means of a 5-year observational study and a 1-year experimental study. Parents and offspring were fitted with radio-transmitters in order to reveal the parental care strategy (i.e. care or desert) of individual parents, and to keep track of the broods post-fledging. We found that 70 per cent of the females from non-experimental nests deserted, while their partner continued to care for their joint offspring alone. Desertion rate was positively related to natural prey population densities and body reserves of the male partner. In response to food supplementation, a larger proportion of the females deserted, and females deserted the offspring at an earlier age. Offspring survival during the post-fledging period tended to be lower in deserted than in non-deserted broods. We argue that the most important benefit of deserting may be remating (sequential polyandry).

Eldegard, Katrine; Sonerud, Geir A.

2009-01-01

177

Factors Driving the Abundance of Ixodes ricinus Ticks and the Prevalence of Zoonotic I. ricinus-Borne Pathogens in Natural Foci  

PubMed Central

Environmental factors may drive tick ecology and therefore tick-borne pathogen (TBP) epidemiology, which determines the risk to animals and humans of becoming infected by TBPs. For this reason, the aim of this study was to analyze the influence of environmental factors on the abundance of immature-stage Ixodes ricinus ticks and on the prevalence of two zoonotic I. ricinus-borne pathogens in natural foci of endemicity. I. ricinus abundance was measured at nine sites in the northern Iberian Peninsula by dragging the vegetation with a cotton flannelette, and ungulate abundance was measured by means of dung counts. In addition to ungulate abundance, data on variables related to spatial location, climate, and soil were gathered from the study sites. I. ricinus adults, nymphs, and larvae were collected from the vegetation, and a representative subsample of I. ricinus nymphs from each study site was analyzed by PCR for the detection of Borrelia burgdorferi sensu lato and Anaplasma phagocytophilum DNA. Mean prevalences of these pathogens were 4.0% ± 1.8% and 20.5% ± 3.7%, respectively. Statistical analyses confirmed the influence of spatial factors, climate, and ungulate abundance on I. ricinus larva abundance, while nymph abundance was related only to climate. Interestingly, cattle abundance rather than deer abundance was the main driver of B. burgdorferi sensu lato and A. phagocytophilum prevalence in I. ricinus nymphs in the study sites, where both domestic and wild ungulates coexist. The increasing abundance of cattle seems to increase the risk of other hosts becoming infected by A. phagocytophilum, while reducing the risk of being infected by B. burgdorferi sensu lato. Controlling ticks in cattle in areas where they coexist with wild ungulates would be more effective for TBP control than reducing ungulate abundance.

Fernandez-de-Mera, Isabel G.; Acevedo, Pelayo; Gortazar, Christian; de la Fuente, Jose

2012-01-01

178

?15N constraints on long-term nitrogen balances in temperate forests.  

PubMed

Biogeochemical theory emphasizes nitrogen (N) limitation and the many factors that can restrict N accumulation in temperate forests, yet lacks a working model of conditions that can promote naturally high N accumulation. We used a dynamic simulation model of ecosystem N and ?(15)N to evaluate which combination of N input and loss pathways could produce a range of high ecosystem N contents characteristic of forests in the Oregon Coast Range. Total ecosystem N at nine study sites ranged from 8,788 to 22,667 kg ha(-1) and carbon (C) ranged from 188 to 460 Mg ha(-1), with highest values near the coast. Ecosystem ?(15)N displayed a curvilinear relationship with ecosystem N content, and largely reflected mineral soil, which accounted for 96-98% of total ecosystem N. Model simulations of ecosystem N balances parameterized with field rates of N leaching required long-term average N inputs that exceed atmospheric deposition and asymbiotic and epiphytic N(2)-fixation, and that were consistent with cycles of post-fire N(2)-fixation by early-successional red alder. Soil water ?(15)NO(3)(-) patterns suggested a shift in relative N losses from denitrification to nitrate leaching as N accumulated, and simulations identified nitrate leaching as the primary N loss pathway that constrains maximum N accumulation. Whereas current theory emphasizes constraints on biological N(2)-fixation and disturbance-mediated N losses as factors that limit N accumulation in temperate forests, our results suggest that wildfire can foster substantial long-term N accumulation in ecosystems that are colonized by symbiotic N(2)-fixing vegetation. PMID:21614618

Perakis, Steven S; Sinkhorn, Emily R; Compton, Jana E

2011-11-01

179

OPRs Of Ammonia versus. 14N/15N Ratios In CN In 15 Comets  

NASA Astrophysics Data System (ADS)

The solar system was formed from interstellar matter 4.6 Gyrs ago and comets are considered as remnants of icy planetesimals formed in the early solar system. One of interesting primordial characters of cometary ice is an ortho-to-para abundance ratio (OPR) of molecules such as H2O, NH3, etc. The OPR probably indicates the molecular formation temperatures in the solar nebula or in the pre-solar molecular cloud. We determined the OPRs of ammonia by using the high dispersion optical spectra of NH2 in 15 comets: C/1995 O1 (Hale-Bopp), C/1999 S4 (LINEAR), C/2001 A2 (LINEAR), C/2000 WM1 (LINEAR), 153P/Ikeya-Zhang, C/2002 V1 (NEAT), C/2002 X5 (Kudo-Fujikawa), C/2002 Y1 (Juels-Holvorcem), C/2001 Q4 (NEAT), C/2002 T7 (LINEAR), C/2003 K4 (LINEAR), 8P/Tuttle, 88P/Howell, 9P/Tempel 1, and 73P-B and -C/Schwassmann-Wachmann 3. The observations were mainly carried out by the Ultraviolet and Visual Echelle Spectrograph (UVES) mounted on the Very Large Telescope (VLT) in Chile. Other telescopes/instruments were also used in some cases. The OPRs of ammonia are determined from OPRs of NH2 (0,9,0) ro-vibronic band around 600 nm. Although absorption lines (by the telluric atmosphere) and cometary C2 emission lines blended affected to NH2 emission lines in this region, we removed them in our analysis. The determined OPRs of ammonia clustered around 30K but not in the cases of 73P-B and -C. This situation is very similar to that of 14N/15N ratios in CN (i.e., 73P-B and -C are quite peculiar relative to other comets). We discuss about the relationship between the OPRs of ammonia and 14N/15N ratios in CN in these 15 comets. Our results indicate the formation of materials at relatively higher temperatures for 73P-B and -C than other comets.

Shinnaka, Yoshiharu; Kawakita, H.; Kobayashi, H.; Jehin, E.; Manfroid, J.; Hutsemékers, D.; Arpigny, C.

2010-10-01

180

Direct contribution of nitrogen deposition to nitrous oxide emissions in a temperate beech and spruce forest - a 15N tracer study  

NASA Astrophysics Data System (ADS)

The impact of atmospheric nitrogen (N) deposition on nitrous oxide (N2O) emissions in forest ecosystems is still unclear. Our study assessed the direct contribution of N deposition to N2O emissions in temperate forests exposed to chronic high N depositions using a 15N labelling technique. In a Norway spruce stand (Picea abies) and in a beech stand (Fagus sylvatica) at the Solling, Germany, we used a low concentrated 15N-labelled ammonium-nitrate solution to simulate N deposition. Nitrous oxide fluxes and 15N isotope abundances in N2O were measured using the closed chamber method combined with 15N isotope analyses. Emissions of N2O were higher in the beech stand (2.6 ± 0.6 kg N ha-1 yr-1) than in the spruce stand (0.3 ± 0.1 kg N ha-1 yr-1). We observed a direct effect of N input on 15N-N2O emissions, which lasted for less than three weeks and was mainly caused by denitrification. No further increase in 15N enrichment of N2O occurred during a one-year experiment, which was probably due to immobilisation of deposited N. The annual emission factor for N2O from deposited N was 0.1% for the spruce stand and 0.6% for the beech stand. Standard methods used in the literature applied to the same stands grossly overestimated emission factors with values of up to 25%. Only 6-13% of the total N2O emissions were derived from direct N depositions. Whether the remaining emissions resulted from accumulated anthropogenic N depositions or native soil N, could not be distinguished with the applied methods. The 15N tracer technique is a useful tool, which may improve estimates of the current contribution of N deposition to N2O emissions.

Eickenscheidt, N.; Brumme, R.; Veldkamp, E.

2011-03-01

181

Resolving the bulk ? 15N values of ancient human and animal bone collagen via compound-specific nitrogen isotope analysis of constituent amino acids  

NASA Astrophysics Data System (ADS)

Stable nitrogen isotope analysis is a fundamental tool in assessing dietary preferences and trophic positions within contemporary and ancient ecosystems. In order to assess more fully the dietary contributions to human tissue isotope values, a greater understanding of the complex biochemical and physiological factors which underpin bulk collagen ? 15N values is necessary. Determinations of ? 15N values of the individual amino acids which constitute bone collagen are necessary to unravel these relationships, since different amino acids display different ? 15N values according to their biosynthetic origins. A range of collagen isolates from archaeological faunal and human bone ( n = 12 and 11, respectively), representing a spectrum of terrestrial and marine protein origins and diets, were selected from coastal and near-coastal sites at the south-western tip of Africa. The collagens were hydrolysed and ? 15N values of their constituent amino acids determined as N-acetylmethyl esters (NACME) via gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). The analytical approach employed accounts for 56% of bone collagen nitrogen. Reconstruction of bulk bone collagen ? 15N values reveals a 2‰ offset from bulk collagen ? 15N values which is attributable to the ? 15N value of the amino acids which cannot currently be determined by GC-C-IRMS, notably arginine which comprises 53% of the nitrogen unaccounted for (23% of the total nitrogen). The ? 15N values of individual amino acids provide insights into both the contributions of various amino acids to the bulk ? 15N value of collagen and the factors influencing trophic position and the nitrogen source at the base of the food web. The similarity in the ? 15N values of alanine, glutamate, proline and hydroxyproline reflects the common origin of their amino groups from glutamate. The depletion in the ? 15N value of threonine with increasing trophic level indicates a fundamental difference between the biosynthetic pathway of threonine and the other amino acids. The ? 15N value of phenylalanine does not change significantly with trophic level, reflecting its conservative nature as an essential amino acid, and thus represents the isotopic composition of the nitrogen at the base of the food web. ? 15N Glu-Phe values in particular are shown to reflect trophic level nitrogen sources within a food web. In relation to the reconstruction of ancient human diet the contribution of marine and terrestrial protein are strongly reflected in ? 15N Glu-Phe values. Differences in nitrogen metabolism are also shown to have an influence upon individual amino acid ? 15N values with ? 15N Glu-Phe values emphasising differences between the different physiological adaptations. The latter is demonstrated in tortoises, which can excrete nitrogen in the form of uric acid and urea and display negative ? 15N Glu-Phe values whereas those for marine and terrestrial mammals are positive. The findings amplify the potential advantages of compound-specific nitrogen isotope analysis in the study of nitrogen flow within food webs and in the reconstruction of past human diets.

Styring, Amy K.; Sealy, Judith C.; Evershed, Richard P.

2010-01-01

182

Sources of variation in consumer-diet ? 15 N enrichment: a meta-analysis  

Microsoft Academic Search

Measurements of 15N of consumers are usually higher than those of their diet. This general pattern is widely used to make inferences about trophic relationships in ecological studies, although the underlying mechanisms causing the pattern are poorly understood. However, there can be substantial variation in consumer-diet 15N enrichment within this general pattern. We conducted an extensive literature review, which yielded

Mathew A. Vanderklift; Sergine Ponsard

2003-01-01

183

Patterns of plant ? 15N values on a Greenland Norse farm  

Microsoft Academic Search

In a further empirical study of the impact of past human activities on modern plant ?15N values, plants were collected in each of two growing seasons from several defined contexts of an inland Norse farm in southwest Greenland. The ?15N measures of the plants show a clear distinction between areas with definite evidence of past human activity and those without.

R. G. Commisso; D. E. Nelson

2007-01-01

184

Accessible NMR Experiments Studying the Hydrodynamics of [superscript 15]N-Enriched Ubiquitin at Low Fields  

ERIC Educational Resources Information Center

We have recently developed and implemented two experiments in biomolecular NMR for an undergraduate-level biophysical chemistry laboratory with commercially available [superscript 15]N-enriched human ubiquitin. These experiments take advantage of [superscript 15]N direct detection of the NMR signal. The first experiment develops skills in…

Thompson, Laura E.; Rovnyak, David

2007-01-01

185

Accessible NMR Experiments Studying the Hydrodynamics of [subscript 15]N-Enriched Ubiquitin at Low Fields  

ERIC Educational Resources Information Center

We have recently developed and implemented two experiments in biomolecular NMR for an undergraduate-level biophysical chemistry laboratory with commercially available [subscript 15]N-enriched human ubiquitin. These experiments take advantage of [subscript 15]N direct detection of the NMR signal. The first experiment develops skills in acquiring…

Thompson, Laura E.; Rovnyak, David

2007-01-01

186

Efeito da materia organica e de um inibidor da nitrificacao na absorcao de (sup 15)N H(sub 4) e (sup 15)N O(sub 3) pelo milho. (The effect of organic matter and nitrification inhibitor on (sup 15) N H(sub 4) and (sup 15) N O(sub 3) absorption by the maize).  

National Technical Information Service (NTIS)

The effect of the forms (sup 15) N H(sub 4) and (sup 15) N O(sub 3) in presence or absence of organic matter and of the nitrification inhibitor AM (2-amino-4-chloro-6-methyl-pyrimidine) in dry matter weight and nitrogen content of the plant derived from s...

S. M. T. Saito

1974-01-01

187

15N and13C NMR investigation of hydroxylamine-derivatized humic substances  

USGS Publications Warehouse

Five fulvic and humic acid samples of diverse origins were derivatized with 15N-labeled hydroxylamine and analyzed by liquid-phase 15N NMR spectrometry. The 15N NMR spectra indicated that hydroxylamine reacted similarly with all samples and could discriminate among carbonyl functional groups. Oximes were the major derivatives; resonances attributable to hydroxamic acids, the reaction products of hydroxylamine with esters, and resonances attributable to the tautomeric equilibrium position between the nitrosophenol and monoxime derivatives of quinones, the first direct spectroscopic evidence for quinones, also were evident. The 15N NMR spectra also suggested the presence of nitriles, oxazoles, oxazolines, isocyanides, amides, and lactams, which may all be explained in terms of Beckmann reactions of the initial oxime derivatives. INEPT and ACOUSTIC 15N NMR spectra provided complementary information on the derivatized samples. 13C NMR spectra of derivatized samples indicated that the ketone/quinone functionality is incompletely derivatized with hydroxylamine. ?? 1991 American Chemical Society.

Thorn, K. A.; Arterburn, J. B.; Mikita, M. A.

1992-01-01

188

Using a macroalgal ?15N bioassay to detect cruise ship waste water effluent inputs.  

PubMed

Green macroalgae bioassays were used to determine if the ?15N signature of cruise ship waste water effluent (CSWWE) could be detected in a small harbor. Opportunistic green macroalgae (Ulva spp.) were collected, cultured under nutrient depleted conditions and characterized with regard to N content and ?15N. Samples of algae were used in controlled incubations to evaluate the direction of isotope shift from exposure to CSWWE. Algae samples exposed to CSWWE exhibited an increase of 1-2.5‰ in ?15N values indicating that the CSWWE had an enriched isotope signature. In contrast, algae samples exposed to field conditions exhibited a significant decrease in the observed ?15N indicating that a light N source was used. Isotopically light, riverine nitrogen derived from N2-fixing trees in the watershed may be a N source utilized by algae. These experiments indicate that the ?15N CSWWE signature was not detectable under the CSWWE loading conditions of this experiment. PMID:21683418

Kaldy, James

2011-08-01

189

Silver(I) complexes of selenourea ( 13 C and 15 N labeled); characterization by 13 C, 15 N and 107 Ag NMR  

Microsoft Academic Search

Silver(I) complexes of selenourea (Seu), Ag(Seu)NO3 and Ag(Seu)2NO3 have been prepared and characterized by elemental analysis, IR and NMR (1H,13C,15N and 107Ag) spectroscopy. An upfield shift in 13C NMR and downfield shifts in 1H and 15N NMR for selenourea resonances are consistent with the selenium coordination to Ag(I). In 107Ag NMR, the AgNO3 signal is deshielded by more than 600

Saeed Ahmad; Anvarhusein A. Isab

2002-01-01

190

Natural Abundance 43Ca NMR Spectroscopy of Tobermorite and Jennite: Model Compounds for C–S–H  

SciTech Connect

There are few effective methods for characterizing the molecular scale structural environments of Ca21 in hydrated cements, which has limited our ability to understand the structure of, for example, Ca–silicate hydrate (C–S–H). 43Ca nuclear magnetic resonance (NMR) spectroscopy has long been considered too insensitive to provide useful data in this regard, but 43Ca magic angle spinning (MAS) NMR spectra reported here for synthetic tobermorite and jennite with naturally abundant levels of 43Ca demonstrate that this is a viable approach.We show that spectra with useful signal/noise ratios can be obtained in a reasonable acquisition period (B2 days) using an H0 field strength of 21.1 T, 5 mm rotors spinning at a frequency of 5 kHz, and a double frequency sweep preparatory pulse sequence. Tobermorite and jennite produce relatively broad resonances due to their complex structures and structural disorder, however, the chemical shift differences between six-coordinate 43Ca in jennite and seven-coordinate 43Ca in 11A ° tobermorite are large enough that the signals are entirely resolved at this field. These data suggest that signal from ideal tobermorite-like and jennite-like sites in cement C–S–H can most likely be distinguished by 43Ca NMR and that this method will be a powerful approach for studying cement-based ceramic materials in the coming decade.

Bowers, Geoffrey M.; Kirkpatrick, Robert J.

2009-02-13

191

Natural Abundance 43Ca NMR Spectroscopy of Tobermorite and Jennite: Model Compounds for C–S–H  

SciTech Connect

There are few effective methods for characterizing the molecular scale structural environments of Ca2? in hydrated cements, which has limited our ability to understand the structure of, for example, Ca–silicate hydrate (C–S–H). 43Ca nuclear magnetic resonance (NMR) spectroscopy has long been considered too insensitive to provide useful data in this regard, but 43Ca magic angle spinning (MAS) NMR spectra reported here for synthetic tobermorite and jennite with naturally abundant levels of 43Ca demonstrate that this is a viable approach.We show that spectra with useful signal/noise ratios can be obtained in a reasonable acquisition period (~2 days) using an H? field strength of 21.1 T, 5 mm rotors spinning at a frequency of 5 kHz, and a double frequency sweep preparatory pulse sequence. Tobermorite and jennite produce relatively broad resonances due to their complex structures and structural disorder, however, the chemical shift differences between six-coordinate 43Ca in jennite and seven-coordinate 43Ca in 11? tobermorite are large enough that the signals are entirely resolved at this field. These data suggest that signal from ideal tobermorite-like and jennite-like sites in cement C–S–H can most likely be distinguished by 43Ca NMR and that this method will be a powerful approach for studying cement-based ceramic materials in the coming decade.

Bowers, Geoffrey M.; Kirkpatrick, Robert J.

2009-02-13

192

Mapping the dynamics of ligand reorganization via 13CH3 and 13CH2 relaxation dispersion at natural abundance  

PubMed Central

Flexible ligands pose challenges to standard structure-activity studies since they frequently reorganize their conformations upon protein binding and catalysis. Here, we demonstrate the utility of side chain 13C relaxation dispersion measurements to identify and quantify the conformational dynamics that drive this reorganization. The dispersion measurements probe methylene 13CH2 and methyl 13CH3 groups; the latter are highly prevalent side chain moieties in known drugs. Combining these side chain studies with existing backbone dispersion studies enables a comprehensive investigation of µs–ms conformational dynamics related to binding and catalysis. We perform these measurements at natural 13C abundance, in congruence with common pharmaceutical research settings. We illustrate these methods through a study of the interaction of a phosphopeptide ligand with the peptidyl-prolyl isomerase, Pin1. The results illuminate the side-chain moieties that undergo conformational readjustments upon complex formation. In particular, we find evidence that multiple exchange processes influence the side chain dispersion profiles. Collectively, our studies illustrate how side-chain relaxation dispersion can shed light on ligand conformational transitions required for activity, and thereby suggest strategies for its optimization.

Wilson, Brian D.; Namanja, Andrew T.

2010-01-01

193

Natural Abundance Carbon Isotope Composition of Isoprene Reflects Incomplete Coupling between Isoprene Synthesis and Photosynthetic Carbon Flow  

PubMed Central

Isoprene emission from leaves is dynamically coupled to photosynthesis through the use of primary and recent photosynthate in the chloroplast. However, natural abundance carbon isotope composition (?13C) measurements in myrtle (Myrtus communis), buckthorn (Rhamnus alaternus), and velvet bean (Mucuna pruriens) showed that only 72% to 91% of the variations in the ?13C values of fixed carbon were reflected in the ?13C values of concurrently emitted isoprene. The results indicated that 9% to 28% carbon was contributed from alternative, slow turnover, carbon source(s). This contribution increased when photosynthesis was inhibited by CO2-free air. The observed variations in the ?13C of isoprene under ambient and CO2-free air were consistent with contributions to isoprene synthesis in the chloroplast from pyruvate associated with cytosolic Glc metabolism. Irrespective of alternative carbon source(s), isoprene was depleted in 13C relative to mean photosynthetically fixed carbon by 4‰ to 11‰. Variable 13C discrimination, its increase by partially inhibiting isoprene synthesis with fosmidomicin, and the associated accumulation of pyruvate suggested that the main isotopic discrimination step was the deoxyxylulose-5-phosphate synthase reaction.

Affek, Hagit P.; Yakir, Dan

2003-01-01

194

In VivoQuantitation of Cerebral Metabolite Concentrations Using Natural Abundance 13C MRS at 1.5 T  

NASA Astrophysics Data System (ADS)

A method for the quantitation of cerebral metabolites on a clinical MR scanner by natural abundance 13C MRS in vivois described. Proton-decoupled spectra were acquired with a power deposition within FDA guidelines using a novel coil design. myo-Inositol, quantified by a separate proton MRS, and readily detectable in 13C MRS, was used as an internal reference. Normal concentrations, measured in four control subjects, age 7 months to 12 years, were glutamate 9.9 ± 0.7, glutamine 5.6 ± 1.0, and NAA 8.8 ± 2.8 mmol/kg. In a patient diagnosed with Canavan disease, examined four times, glutamate was reduced to 46% of normal, 4.6 ± 0.5 mmol/kg. NAA was increased by 50% to 13.2 ± 1.6 mmol/kg in 13C MRS, consistent with the 41% increase to 12.3 ± 1.1 from control 8.7 ± 1.1 mmol/kg assayed by 1H MRS. Limited concentration of glutamate may impact on glutamatergic neurons and excitatory neurotransmission in Canavan disease. Quantitation of cerebral glutamate in human brain may have clinical value in human neuropathologies in which glutamate is believed to play a central role.

Blüml, Stefan

1999-02-01

195

Climate-Dependence of Plant-Soil 15N/14N Interactions Across Tropical Rainforests  

NASA Astrophysics Data System (ADS)

In most areas of the world, the 15N/14N of bulk soils is higher than that of plant leaves, and the isotopic signatures of these two ecosystem N pools progressively diverge with increasing rainfall. However, both the cause for this isotopic trend and its implications for understanding interactions between climate and N cycles are largely unknown. We report 15N/14N measurements of nitrate, ammonium, and total dissolved N in soil extracts from a highly constrained rainfall sequence in Hawaii, across which this trend in ecosystem 15N/14N is captured, to examine the competing explanations for plant-soil 15N/14N uncouplings. While the isotopic influences of microbial transfers of N between nitrate and ammonium pools and plant-mycorrhizae interactions have been posited in plant-soil 15N/14N relationships, our data did not support an important role for either of these mechanisms. Instead, preferential regeneration of 14N during the breakdown of DON to ammonium explains why the 15N/14N of plants is lower than that of bulk soils. Fractionation at this step leads to two isotopically distinct N subcycles in each forest, a lower-15N/14N subcycle composed of ammonium, nitrate, and bulk plant biomass N that `spins' rapidly and a higher-15N/14N subcycle composed of bulk soil N and DON that is much less dynamic. The increased difference between soil and plant 15N/14N is due to changes in the impacts of nitrification and denitrification on the 15N/14N of ammonium and nitrate, coupled with a switch from nitrate to ammonium uptake by plants under the wettest conditions. For instance, the particularly large (~6 per mil) 15N/14N difference between plants and soils in the wettest sites is due to the lack of 15N-enrichment of ammonium by nitrification coupled with plant dependence on ammonium uptake only. Our results highlight the importance of interactions between DON breakdown, ecosystem N recycling, and gaseous N losses in the explaining the interactions between the 15N signatures of soils and plants across these tropical rainforests. We also show that these interactions are climate-dependent.

Houlton, B. Z.; Sigman, D. M.; Hedin, L. O.

2005-12-01

196

Production of 15N-depleted biomass during cyanobacterial N2-fixation at high Fe concentrations  

NASA Astrophysics Data System (ADS)

In this study we examine the effects of varying Fe, Mo, and P concentrations on ?15N fractionation during N2 fixation in the cyanobacterium Anabaena variabilis. We show that when grown in Fe-enriched media ([Fe] ? 50 nM), this organism produces biomass up to 3‰ lower in ?15N than when grown in Fe-limited media ([Fe] < 50 nM). A compilation of our data with previous measurements of ?15N in N2-fixing cyanobacteria reveals a general trend toward the production of more 15N-depleted biomass at higher Fe concentrations. We discuss our results in the context of negative ?15N values preserved in Archean and some Phanerozoic sediments, generally attributed to the production of marine organic matter with low ?15N by N2 fixation (and potentially NH4+ regeneration) during periods of fluctuating nutrient dynamics. We suggest that enhanced Fe availability during periods of widespread ocean anoxia can further stimulate the production of 15N-depleted biomass by N2-fixing organisms, contributing to the isotopic record.

Zerkle, Aubrey L.; Junium, Christopher K.; Canfield, Donald E.; House, Christopher H.

2008-09-01

197

A Survey of \\\\delta18O and \\\\delta15N Ratios in Ground Water from an Agricultural Community in the San Joaquin Valley, California  

Microsoft Academic Search

We studied ground water samples from domestic and monitoring wells in an agricultural community in the eastern side of the San Joaquin Valley, California. The study area is rich in alluvial soils creating an extremely fertile farmland. Livestock farms and agricultural fields are abundant in the area. Fifty-four ground water samples were analyzed for \\\\delta18O and \\\\delta15N in dissolved nitrate,

S. D. Glowacki; C. J. Suen

2004-01-01

198

Linking dynamics of soil microbial phospholipid fatty acids to carbon mineralization in a 13C natural abundance experiment: Impact of heavy metals and acid rain  

Microsoft Academic Search

A 13C natural abundance experiment including GC-c-IRMS analysis of phospholipid fatty acids (PLFAs) was conducted to assess the temporal dynamics of the soil microbial community and carbon incorporation during the mineralization of plant residues under the impact of heavy metals and acid rain. Maize straw was incorporated into (i) control soil, (ii) soil irrigated with acid rain, (iii) soil amended

Michael Stemmer; Andrea Watzinger; Karl Blochberger; Georg Haberhauer; Martin H. Gerzabek

2007-01-01

199

sup 14,15 N, sup 13 C, sup 57 Fe, and sup 1,2 H Q-band ENDOR study of Fe-S proteins with clusters that have endogenous sulfur ligands  

SciTech Connect

The benefits of performing ENDOR experiments at higher microwave frequency are demonstrated in a Q-band (35 GHz) ENDOR investigation of a number of proteins with (nFe-mS) clusters, n = 2,3,4. Each protein displays several resonances in the frequency range of 0-20 MHz. In all instances, features are seen near {nu} {approx} 13 and 8 MHz that can be assigned, respectively, to distant ENDOR from {sup 13}C in natural-abundance (1.1%) and from {sup 14}N. In addition, a number of proteins show local {sup 13}C ENDOR signals with resolved hyperfine interactions; these are assigned to the {beta} carbons of cysteines bound to the cluster. Quadrupole coupling constants are derived for both local and distant {sup 14}N signals. The interpretation of the data is supported by studies on {sup 15}N- and {sup 13}C-enriched ferredoxin (Fd) from Anabaena 7120, where the {sup 15}N signals can be clearly correlated with the corresponding {sup 14}N signals and where the {sup 13}C signals are strongly enhanced. Thus, the observation of {sup 14}N {Delta}m{sub I} = {plus minus} 2 signals at Q-band provides a new technique for examining weak interactions with a cluster. Six proteins show an additional pattern near {nu} {approx} 18 MHz that arises from {sup 57}Fe in natural abundance (2.2%) with A({sup 57}Fe) {approx} 36 MHz, which opens the possibility of studying proteins for which enrichment is impractical. Q-band ENDOR studies also have been carried out on four {sup 2}H-exchanged Fe-S proteins, and ENDOR detects exchangeable protons in each. The importance of these findings for the interpretation of X- and Q-band ENDOR at low radiofrequencies is discussed.

Houseman, A.L.P.; Chaoliang Fan; Werst, M.M.; Hoffman, B.M. (Northwestern Univ., Evanston, IL (United States)); Byungha Oh; Markley, J.L. (Univ. of Wisconsin, Madison (United States)); Kennedy, M.C.; Beinert, H. (Medical College of Wisconsin, Milwaukee (United States))

1992-02-25

200

Covalent binding of reduced metabolites of [{sup 15}N{sub 3}]TNT to soil organic matter during a bioremediation process analyzed by {sup 15}N NMR spectroscopy  

SciTech Connect

Evidence is presented for the covalent binding of biologically reduced metabolites of 2,4,6-{sup 15}N{sub 3}-trinitrotoluene (TNT) to different soil fractions, using liquid {sup 15}N NMR spectroscopy. A silylation procedure was used to release soil organic matter from humin and whole soil for spectroscopic measurements. TNT-contaminated soil was spiked with 2,4,6-{sup 15}N{sub 3}-trinitrotoluene and {sup 14}C-ring labeled TNT, before treatment in a soil slurry reactor. During the anaerobic/aerobic incubation the amount of radioactivity detected in the fulvic and humic acid fractions did not change significantly whereas the radioactivity bound to humin increased to 71%. The {sup 15}N NMR spectra of the fulvic acid samples were dominated by a large peak that corresponded to aliphatic amines or ammonia. In the early stages of incubation, {sup 15}N NMR analysis of the humic acids indicated bound azoxy compounds. The signals arising from nitro and azoxy groups disappeared with further anaerobic treatment. At the end of incubation, the NMR shifts showed that nitrogen was covalently bound to humic acid as substituted amines and amides. The NMR spectra of the silylated humin suggest formation of azoxy compounds and imine linkages. Bound metabolites possessing nitro groups were also detected. Primary amines formed during the anaerobic incubation disappeared during the aerobic treatment. Simultaneously, the amount of amides and tertiary amines increased. Nitro and azoxy groups of bound molecules were still present in humin at the end of the incubation period. Formation of azoxy compounds from partially reduced TNT followed by binding and further reduction appears to be an important mechanism for the immobilization of metabolites of TNT to soil.

Achtnich, C.; Fernandes, E.; Bollag, J.M.; Knackmuss, H.J.; Lenke, H.

1999-12-15

201

Mammalian DNA ?15N exhibits 40? intramolecular variation and is unresponsive to dietary protein level  

PubMed Central

We report the first high precision characterization of molecular and intramolecular ?15N of nucleosides derived from mammalian DNA. The influence of dietary protein level on brain amino acids and deoxyribonucleosides was determined to investigate whether high protein turnover would alter amino acid 15N or 13C. Pregnant guinea pig dams were fed control diets, or high or low levels of dietary protein throughout gestation, and all pups were fed control diets. Cerebellar DNA of offspring was extracted at 2 and 120 days of life, nucleosides isolated and ?15N and ?13C characterized. Mean diet ?15N = 0.45±0.33‰, compared to cerebellar whole tissue and DNA ?15N = +4.1±0.7‰ and ?4.5±0.4‰, respectively. Cerebellar deoxythymidine (dT), deoxycytidine (dC), deoxyadenosine (dA), and deoxyguanosine (dG) ?15N were +1.4±0.4, ?2.1±0.9, ?7.2±0.3, and ?10.4±0.5‰, respectively. There were no changes in amino acid or deoxyribonucleoside ?15N due to dietary protein level. Using known metabolic relationships, we developed equations to calculate the intramolecular ?15N originating from aspartate (asp) in purines (pur) or pyrimidines (pyr), glutamine (glu), and glycine (gly) to be ?15NASP-PUR, ?15NASP-PYR, ?15NGLN, and ?15NGLY +11.9±2.3‰, +7.0±2.0‰, ?9.1±2.4‰, and ?31.8±8.9‰, respectively. A subset of twelve amino acids from food and brain had mean ?15N of 4.3±3.2‰ and 13.8±3.1‰, respectively, and ?15N for gly and asp were 12.6±2.2‰ and 15.2±0.8‰, respectively. A separate isotope tracer study detected no significant turnover of cerebellar DNA in the first six months of life. The large negative ?15N difference between gly and cerebellar purine N at the gly (7) position implies either that there is a major isotope effect during DNA synthesis, or that in utero gly has a different isotope ratio during rapid growth and metabolism than in adult life. Our data show that cerebellar nucleoside intramolecular ?15N vary over more than 40‰ and are not influenced by dietary protein level or age.

Strable, Maggie S.; Tschanz, Carolyn L.; Varamini, Behzad; Chikaraishi, Yoshito; Ohkouchi, Naohiko; Brenna, J. Thomas

2014-01-01

202

Biomonitoring of traffic-related nitrogen oxides in the Maurienne valley (Savoie, France), using purple moor grass growth parameters and leaf (15)N/(14)N ratio.  

PubMed

Effects of traffic-related nitrogenous emissions on purple moor grass (Molinia caerulea (L.) Moench) transplants, used here as a new biomonitoring species, were assessed along 500 m long transects orthogonal to roads located in two open areas in the Maurienne valley (French Alps). Leaves were sampled during summer 2004 and 2005 for total N-content and (15)N-abundance determination while nitrogen oxides (NO and NO(2)) concentrations were determined using passive diffusion samplers. A significant and negative correlation was observed between plant total N-content, and (15)N-abundance and the logarithm of the distance to the road axis. The strongest decreases in plant N parameters were observed between 15 and 100 m from road axis. They were equivalent to background levels at a distance of about 800 m from the roads. In addition, motor vehicle pollution significantly affected vegetation at road edge, as was established from the relationship between leaf (15)N-abundance, total N-content and road traffic densities. PMID:20045586

Laffray, Xavier; Rose, Christophe; Garrec, Jean-Pierre

2010-05-01

203

Continuous field measurement of N2O isotopologues using FTIR spectroscopy following 15N addition  

NASA Astrophysics Data System (ADS)

Anthropogenic additions of fertilizer nitrogen (N) have significantly increased the mole fraction of nitrous oxide (N2O) in the troposphere. Tracking the fate of fertilizer N and its transformation to N2O is important to advance knowledge of greenhouse gas emissions from soils. Transport and transformations are frequently studied using 15N labeling experiments, but instruments capable of continuous measurements of 15N-N2O at the surface of soil have only recently come to the fore. Our primary aim was to quantify emissions of N2O and the fraction of 15N emitted as N2O from an agricultural soil following 15N addition using a mobile Fourier Transform Infrared (FTIR) spectrometer. We set up a short-term field experiment on a coastal floodplain site near Nowra, New South Wales. We deployed an automated chamber system connected to a multi-pass cell (optical pathlength 24 m) and low resolution FTIR spectrometer to measure fluxes of all N2O isotopologues collected from five 0.25 m2 chambers every three hours. We measured N2O fluxes pre and post-application of 15N-labeled substrate as potassium nitrate (KNO3) or urea [CO(NH2)2] to the soil surface. Root mean square uncertainties for all isotopologue measurements were less than 0.3 nmol mol-1 for 1 minute average concentration measurements, and minimum detectable fluxes for each isotopologue were <0.1 ng N m-2 s-1. Emissions of all N2O isotopologues were evident immediately following 15N addition. Emissions of 14N15NO, 15N14NO and 15N15NO isotopologues subsided within 10 d, but 14N14NO fluxes were evident over the entire experiment. The figure provides an overview of the emissions. Cumulative 15N-N2O fluxes (sum of the three 15N isotopologues) per chamber for the 14 days following 15N addition ranged from 1.5 to 10.3 mg 15N-N2O m-2. The chambers were destructively sampled after 2 weeks and 15N analyzed in soil and plant material using isotope ratio mass spectrometry. Approximately 1% (range 0.7 - 1.9%) of the total amount of 15N applied was emitted as N2O. Average fractions of 15N recovered in soil, root, shoot, and microbial biomass pools varied between trials but were approximately 0.4, 0.08, 0.1 and 0.03, respectively. The results indicate that the portable FTIR spectroscopic technique can effectively trace transfer of 15N to the atmosphere as N2O after 15N addition, allowing for powerful quantification of N2O emissions under field conditions.

Phillips, R. L.; Griffith, D. W.; Dijkstra, F. A.; Lugg, G.; Lawrie, R.; Macdonald, B.

2012-12-01

204

?(15)N variation in Ulva lactuca as a proxy for anthropogenic nitrogen inputs in coastal areas of Gulf of Gaeta (Mediterranean Sea).  

PubMed

We tested the capacity of Ulva lactuca to mark N sources across large marine areas by measuring variation in its ?(15)N at several sites in the Gulf of Gaeta. Comparisons were made with the macroalga Cystoseira amentacea. Variation of ?(15)N values was assessed also in the coastal waters off the Circeo Natural Park, where U. lactuca and C. amentacea were harvested, as these waters are barely influenced by human activities and were used as reference site. A small fragment from each frond was preserved before deployment in order to characterize the initial isotopic values. After 48h of submersion, U. lactuca was more responsive than C. amentacea to environmental variation and ?(15)N enrichment in the Gulf of Gaeta was observed. The spatial distribution of ?(15)N enrichment indicated that different macro-areas in the Gulf were affected by N inputs from different origins. Comparison of the ?(15)N values of fragments taken from the same transplanted frond avoided bias arising from natural isotopic variability. PMID:24923814

Orlandi, Lucia; Bentivoglio, Flavia; Carlino, Pasquale; Calizza, Edoardo; Rossi, David; Costantini, Maria Letizia; Rossi, Loreto

2014-07-15

205

Natural-abundance stable carbon isotopes of small-subunit ribosomal RNA (SSU rRNA) from Guaymas Basin (Mexico)  

NASA Astrophysics Data System (ADS)

Small-subunit ribosomal RNA (SSU rRNA) is a phylogenetically informative molecule found in all species. Because it is poorly preserved in most environments, it is a useful marker for active microbial populations. We are using the natural-abundance stable carbon isotopic composition of specific microbial groups to help identify the carbon substrates contributing to microbial biomass in a variety of marine environments. At Guaymas Basin, hydrothermal fluids interact with abundant sedimentary organic carbon to produce natural gas and petroleum. Where this reaches the sediment surface, it can support dense patches of seafloor life, including Beggiatoa mats. We report here on the stable carbon isotopic composition of SSU rRNA from a Beggiatoa mat transect, a cold background site, a warm site with high oil concentration, and a second Beggiatoa mat. The central part of the transect mat overlay the steepest temperature gradient, and was visually dominated by orange Beggiatoa. This was fringed by white Beggiatoa mat and bare, but still warm, sediment. Methane concentrations were saturating beneath the orange and white mats and at the oily site, lower beneath bare sediment, and below detection at the background site. Our initial hypotheses were that rRNA isotopic composition would be strongly influenced by methane supply, and that archaeal rRNA might be lighter than bacterial due to contributions from methanogens and anaerobic methane oxidizers. We used biotin-labeled oligonucleotides to capture Bacterial and Archaeal SSU rRNA for isotopic determination. Background-site rRNA was isotopically heaviest, and bacterial RNA from below 2 cm at the oily site was lightest, consistent with control by methane. Within the transect mat, however, the pattern was more complicated; at some sediment depths, rRNA from the mat periphery was isotopically lightest. Part of this may be due to the spatially and temporally variable paths followed by hydrothermal fluid, which can include horizontal flow. There was no consistent isotopic difference between rRNAs captured by the two probes, although RNA recoveries were too low for isotopic determinations at depths where methanogens and methane oxidizers are expected. Our prediction that rRNA stable carbon isotopic composition would correlate with methane supply was borne out by the comparison between background and mat sediments, but may be an oversimplification for sites within hydrothermal features. Future work will include the isotopic characterization of other potential carbon substrates, such as acetate. We are also investigating cold-seep sediments and brine pools in the Gulf of Mexico, where methane is significantly more 13C-depleted than at Guaymas Basin and may therefore leave a stronger imprint on microbial biomass.table carbon isotopes of rRNA captured with Bacterial and Archaeal probes at mat transect and background sites.

MacGregor, B. J.; Mendlovitz, H.; Albert, D.; Teske, A. P.

2012-12-01

206

Acceleration of natural-abundance solid-state MAS NMR measurements on bone by paramagnetic relaxation from gadolinium-DTPA.  

PubMed

Reducing the data collection time without affecting the signal intensity and spectral resolution is one of the major challenges for the widespread application of multidimensional nuclear magnetic resonance (NMR) spectroscopy, especially in experiments conducted on complex heterogeneous biological systems such as bone. In most of these experiments, the NMR data collection time is ultimately governed by the proton spin-lattice relaxation times (T1). For over two decades, gadolinium(III)-DTPA (Gd-DTPA, DTPA=Diethylene triamine pentaacetic acid) has been one of the most widely used contrast-enhancement agents in magnetic resonance imaging (MRI). In this study, we demonstrate that Gd-DTPA can also be effectively used to enhance the longitudinal relaxation rates of protons in solid-state NMR experiments conducted on bone without significant line-broadening and chemical-shift-perturbation side effects. Using bovine cortical bone samples incubated in different concentrations of Gd-DTPA complex, the (1)H T1 values were calculated from data collected by (1)H spin-inversion recovery method detected in natural-abundance (13)C cross-polarization magic angle spinning (CPMAS) NMR experiments. Our results reveal that the (1)H T1 values can be successfully reduced by a factor of 3.5 using as low as 10mM Gd-DTPA without reducing the spectral resolution and thus enabling faster data acquisition of the (13)C CPMAS spectra. These results obtained from (13)C-detected CPMAS experiments were further confirmed using (1)H-detected ultrafast MAS experiments on Gd-DTPA doped bone samples. This approach considerably improves the signal-to-noise ratio per unit time of NMR experiments applied to bone samples by reducing the experimental time required to acquire the same number of scans. PMID:24881032

Mroue, Kamal H; Zhang, Rongchun; Zhu, Peizhi; McNerny, Erin; Kohn, David H; Morris, Michael D; Ramamoorthy, Ayyalusamy

2014-07-01

207

Acceleration of natural-abundance solid-state MAS NMR measurements on bone by paramagnetic relaxation from gadolinium-DTPA  

NASA Astrophysics Data System (ADS)

Reducing the data collection time without affecting the signal intensity and spectral resolution is one of the major challenges for the widespread application of multidimensional nuclear magnetic resonance (NMR) spectroscopy, especially in experiments conducted on complex heterogeneous biological systems such as bone. In most of these experiments, the NMR data collection time is ultimately governed by the proton spin-lattice relaxation times (T1). For over two decades, gadolinium(III)-DTPA (Gd-DTPA, DTPA = Diethylene triamine pentaacetic acid) has been one of the most widely used contrast-enhancement agents in magnetic resonance imaging (MRI). In this study, we demonstrate that Gd-DTPA can also be effectively used to enhance the longitudinal relaxation rates of protons in solid-state NMR experiments conducted on bone without significant line-broadening and chemical-shift-perturbation side effects. Using bovine cortical bone samples incubated in different concentrations of Gd-DTPA complex, the 1H T1 values were calculated from data collected by 1H spin-inversion recovery method detected in natural-abundance 13C cross-polarization magic angle spinning (CPMAS) NMR experiments. Our results reveal that the 1H T1 values can be successfully reduced by a factor of 3.5 using as low as 10 mM Gd-DTPA without reducing the spectral resolution and thus enabling faster data acquisition of the 13C CPMAS spectra. These results obtained from 13C-detected CPMAS experiments were further confirmed using 1H-detected ultrafast MAS experiments on Gd-DTPA doped bone samples. This approach considerably improves the signal-to-noise ratio per unit time of NMR experiments applied to bone samples by reducing the experimental time required to acquire the same number of scans.

Mroue, Kamal H.; Zhang, Rongchun; Zhu, Peizhi; McNerny, Erin; Kohn, David H.; Morris, Michael D.; Ramamoorthy, Ayyalusamy

2014-07-01

208

15N/ 14N and 18O/ 16O stable isotope ratios of nitrous oxide produced during denitrification in temperate forest soils  

NASA Astrophysics Data System (ADS)

Anaerobic incubations of upland and wetland temperate forest soils from the same watershed were conducted under different moisture and temperature conditions. Rates of nitrous oxide (N 2O) production by denitrification of nitrate ( NO3-) and the stable isotopic composition of the N 2O (? 15N, ? 18O) were measured. In all soils, N 2O production increased with elevated temperature and soil moisture. At each temperature and moisture level, the rate of N 2O production in the wetland soil was greater than in the upland soil. The 15N isotope effect (?) (product - substrate) ranged from -20‰ to -29‰. These results are consistent with other published estimates of 15N fractionation from both single species culture experiments and soil incubation studies from different ecosystems. A series of incubations were conducted with 18O-enriched water (H 2O) to determine if significant oxygen exchange (O-exchange) occurred between H 2O and N 2O precursors during denitrification. The exchange of H 2O-O with nitrite ( NO2-) and/or nitric oxide (NO) oxygen has been documented in single organism culture studies but has not been demonstrated in soils prior to this study. The fraction of N 2O-O derived from H 2O-O was confined to a strikingly narrow range that differed between soil types. H 2O-O incorporation into N 2O produced from upland and wetland soils was 86% to 94% and 64% to 70%, respectively. Neither the temperature, soil moisture, nor the rate of N 2O production influenced the magnitude of O-exchange. With the exception of one treatment, the net 18O isotope effect (? net) (product-substrate) ranged from +37‰ to +43‰. Most previous studies that have reported 18O isotope effects for denitrification of NO3- to N 2O have failed to account for the effect of oxygen exchange with H 2O. When high amounts of O-exchange occur after fractionation during reductive O-loss, the 18O-enrichment is effectively lost or diminished and ? 18O-N 2O values will be largely dictated by ? 18O-H 2O values and subsequent fractionation. The process and extent of O-exchange, combined with the magnitude of oxygen isotope fractionation at each reduction step, appear to be the dominant controls on the observed oxygen isotope effect. In these experiments, significant oxygen isotope fractionation was observed to occur after the majority of water O-exchange. Due to the importance of O-exchange, the net oxygen isotope effect for N 2O production in soils can only be determined using ? 18O-H 2O addition experiments with ? 18O-H 2O close to natural abundance. The results of this study support the continued use of ? 15N-N 2O analysis to fingerprint N 2O produced from the denitrification of NO3-. The utilization of 18O/ 16O ratios of N 2O to study N 2O production pathways in soil environments is complicated by oxygen exchange with water, which is not usually quantified in field studies. The oxygen isotope fractionation observed in this study was confined to a narrow range, and there was a clear difference in water O-exchange between soil types regardless of temperature, soil moisture, and N 2O production rate. This suggests that 18O/ 16O ratios of N 2O may be useful in characterizing the actively denitrifying microbial community.

Snider, David M.; Schiff, Sherry L.; Spoelstra, John

2009-02-01

209

Variability in the bulk composition and abundance of dissolved organic matter in the lower Mississippi and Pearl rivers  

Microsoft Academic Search

In this study, we examined the temporal and spatial variability of dissolved organic matter (DOM) abundance and composition in the lower Mississippi and Pearl rivers and effects of human and natural influences. In particular, we looked at bulk C\\/N ratio, stable isotopes (?15N and ?13C) and 13C nuclear magnetic resonance (NMR) spectrometry of high molecular weight (HMW; 0.2 ?m to

Shuiwang Duan; Thomas S. Bianchi; Alan M. Shiller; Karl Dria; Patrick G. Hatcher; Kevin R. Carman

2007-01-01

210

Variability in the bulk composition and abundance of dissolved organic matter in the lower Mississippi and Pearl rivers  

Microsoft Academic Search

In this study, we examined the temporal and spatial variability of dissolved organic matter (DOM) abundance and composition in the lower Mississippi and Pearl rivers and effects of human and natural influences. In particular, we looked at bulk C\\/N ratio, stable isotopes (delta 15N and delta 13C) and 13C nuclear magnetic resonance (NMR) spectrometry of high molecular weight (HMW; 0.2

Shuiwang Duan; Thomas S. Bianchi; Alan M. Shiller; Karl Dria; Patrick G. Hatcher; Kevin R. Carman

2007-01-01

211

Stable delta(15)N and delta(13)C isotope ratios in aquatic ecosystems.  

PubMed

In the past 20 years, rapid progress in stable isotope (SI) studies has allowed scientists to observe natural ecosystems from entirely new perspectives. This report addresses the fundamental concepts underlying the use of the SI ratio. The unique characteristics of the SI ratio make it an interdisciplinary parameter that acts as a chemical fingerprint of biogenic substances and provides a key to the world of isotopomers. Variations in SI ratios of biogenic substances depend on the isotopic compositions of reactants, the pathways and kinetic modes of reaction dynamics, and the physicochemical conditions. In fact, every biogenic material has its own isotopic composition, its "dynamic SI fingerprint", which is governed by its function and position in the material flow. For example, the relative SI ratio in biota is determined by dietary lifestyle, e.g., the modes of drinking, eating, and excreting, and appears highly regular due to the physicochemical differences of isotopomers. Our primary goal here is to elucidate the general principals of isotope partitioning in major biophilic elements in molecules, biogenic materials, and ecosystems (Wada, E. et al., 1995). To this end, the nitrogen and carbon SI distribution ratios (delta(15)N and delta(13)C, respectively) are used to examine materials cycling, food web structures, and their variability in various kinds of watershed-including aquatic ecosystems to elucidate an "isotopically ordered world". PMID:19282646

Wada, Eitaro

2009-01-01

212

Evaluating microbial carbon sources in Athabasca oil sands tailings ponds using natural abundance stable and radiocarbon isotopes  

NASA Astrophysics Data System (ADS)

Natural abundance stable (?13C) and radiocarbon (?14C) isotopes of phospholipid fatty acids (PLFAs) were used to evaluate the carbon sources utilized by the active microbial populations in surface sediments from Athabasca oil sands tailings ponds. The absence of algal-specific PLFAs at three of the four sites investigated, in conjunction with ?13C signatures for PLFAs that were generally within ~3‰ of that reported for oil sands bitumen (~ -30‰), indicated that the microbial communities growing on petroleum constituents were dominated by aerobic heterotrophs. The ?14C values of PLFAs ranged from -906 to -586‰ and pointed to a significant uptake of fossil carbon (up to ~90% of microbial carbon derived from petroleum), particularly in PLFAs (e.g., cy17:0 and cy19:0) often associated with petroleum hydrocarbon degrading bacteria. The comparatively higher levels of 14C in other, less specific PLFAs (e.g., 16:0) indicated the preferential uptake of younger organic matter by the general microbial population (~50-80% of microbial carbon derived from petroleum). Since the main carbon pools in tailings sediment were essentially 'radiocarbon dead' (i.e., no detectable 14C), the principal source for this modern carbon is considered to be the Athabasca River, which provides the bulk of the water used in the bitumen extraction process. The preferential uptake of the minor amount of young and presumably more biodegradable material present in systems otherwise dominated by recalcitrant petroleum constituents has important implications for remediation strategies. On the one hand, it implies that mining-related organic contaminants could persist in the environment long after tailings pond reclamation has begun. Alternatively, it may be that the young, labile organic matter provided by the Athabasca River plays an important role in stimulating or supporting the microbial utilization of petroleum carbon in oil sands tailings ponds via co-metabolism or priming processes. Further research needs to examine the role which priming processes play in controlling the fate of organic contaminants in Athabasca oil sands tailings ponds, such as understanding to what extent the addition of labile material may hinder or enhance microbial uptake of fossil carbon. This knowledge can be subsequently used to optimize conditions which favour natural attenuation processes in reclamation sites following mine closure.

Ahad, J. M.; Pakdel, H.

2013-12-01

213

Effect of High-energy Resonances on the 18O(p, ?)15N Reaction Rate at AGB and Post-AGB Relevant Temperatures  

NASA Astrophysics Data System (ADS)

The 18O(p, ?)15N reaction is of great importance in several astrophysical scenarios, as it influences the production of key isotopes such as 19F, 18O, and 15N. Fluorine is synthesized in the intershell region of asymptotic giant branch (AGB) stars, together with s-elements, by ? radiative capture on 15N, which in turn is produced in the 18O proton-induced destruction. Peculiar 18O abundances are observed in R-Coronae Borealis stars, having 16O/18O <~ 1, hundreds of times smaller than the galactic value. Finally, there is no definite explanation of the 14N/15N ratio in pre-solar grains formed in the outer layers of AGB stars. Again, such an isotopic ratio is influenced by the 18O(p, ?)15N reaction. In this work, a high accuracy 18O(p, ?)15N reaction rate is proposed, based on the simultaneous fit of direct measurements and of the results of a new Trojan Horse experiment. Indeed, current determinations are uncertain because of the poor knowledge of the resonance parameters of key levels of 19F. In particular, we have focused on the study of the broad 660 keV 1/2+ resonance corresponding to the 8.65 MeV level of 19F. Since ? ~ 100-300 keV, it determines the low-energy tail of the resonant contribution to the cross section and dominates the cross section at higher energies. Here, we provide a reaction rate that is a factor of two larger above T ~ 0.5 109 K based on our new improved determination of its resonance parameters, which could strongly influence present-day astrophysical model predictions.

La Cognata, M.; Spitaleri, C.; Mukhamedzhanov, A. M.

2010-11-01

214

EFFECT OF HIGH-ENERGY RESONANCES ON THE {sup 18}O(p, {alpha}){sup 15}N REACTION RATE AT AGB AND POST-AGB RELEVANT TEMPERATURES  

SciTech Connect

The {sup 18}O(p, {alpha}){sup 15}N reaction is of great importance in several astrophysical scenarios, as it influences the production of key isotopes such as {sup 19}F, {sup 18}O, and {sup 15}N. Fluorine is synthesized in the intershell region of asymptotic giant branch (AGB) stars, together with s-elements, by {alpha} radiative capture on {sup 15}N, which in turn is produced in the {sup 18}O proton-induced destruction. Peculiar {sup 18}O abundances are observed in R-Coronae Borealis stars, having {sup 16}O/{sup 18}O {approx}< 1, hundreds of times smaller than the galactic value. Finally, there is no definite explanation of the {sup 14}N/{sup 15}N ratio in pre-solar grains formed in the outer layers of AGB stars. Again, such an isotopic ratio is influenced by the {sup 18}O(p, {alpha}){sup 15}N reaction. In this work, a high accuracy {sup 18}O(p, {alpha}){sup 15}N reaction rate is proposed, based on the simultaneous fit of direct measurements and of the results of a new Trojan Horse experiment. Indeed, current determinations are uncertain because of the poor knowledge of the resonance parameters of key levels of {sup 19}F. In particular, we have focused on the study of the broad 660 keV 1/2{sup +} resonance corresponding to the 8.65 MeV level of {sup 19}F. Since {Gamma} {approx} 100-300 keV, it determines the low-energy tail of the resonant contribution to the cross section and dominates the cross section at higher energies. Here, we provide a reaction rate that is a factor of two larger above T {approx} 0.5 10{sup 9} K based on our new improved determination of its resonance parameters, which could strongly influence present-day astrophysical model predictions.

La Cognata, M.; Spitaleri, C. [INFN-Laboratori Nazionali del Sud and University of Catania, I-95123 Catania (Italy); Mukhamedzhanov, A. M., E-mail: lacognata@lns.infn.i [Cyclotron Institute-Texas A and M University, College Station, TX (United States)

2010-11-10

215

Nitrification rates and 15N abundances of N2O and NO3- in the western North Pacific  

Microsoft Academic Search

NITROUS oxide plays an important part in atmospheric chemistry; it is a 'greenhouse' gas and has the potential to destroy ozone. Concentrations of N2O in surface waters of the oceans are generally close to equilibrium with the atmosphere, but sub-surface sea water is supersaturated with N2O1-5. The oceans are now regarded as a source4 for atmospheric N2O by production through

Naohiro Yoshida; Hajime Morimoto; Mitsuhiro Hirano; Isao Koike; Sadao Matsuo; Eitaro Wada; Toshiro Saino; Akihiko Hattori

1989-01-01

216

Preparation of 13C/15N-labeled oligomers using the polymerase chain reaction  

DOEpatents

Preparation of .sup.13 C/.sup.15 N-labeled DNA oligomers using the polymerase chain reaction (PCR). A PCR based method for uniform (.sup.13 C/.sup.15 N)-labeling of DNA duplexes is described. Multiple copies of a blunt-ended duplex are cloned into a plasmid, each copy containing the sequence of interest and restriction Hinc II sequences at both the 5' and 3' ends. PCR using bi-directional primers and uniformly .sup.13 C/.sup.15 N-labeled dNTP precursors generates labeled DNA duplexes containing multiple copies of the sequence of interest. Twenty-four cycles of PCR, followed by restriction and purification, gave the uniformly .sup.13 C/.sup.15 N-labeled duplex sequence with a 30% yield. Such labeled duplexes find significant applications in multinuclear magnetic resonance spectroscopy.

Chen, Xian (Los Alamos, NM); Gupta, Goutam (Santa Fe, NM); Bradbury, E. Morton (Santa Fe, NM)

2001-01-01

217

Secondary sup 15 N isotope effects on the reactions catalyzed by alcohol and formate dehydrogenases  

SciTech Connect

Secondary {sup 15}N isotope effects at the N-1 position of 3-acetylpyridine adenine dinucleotide have been determined, by using the internal competition technique, for horse liver alcohol dehydrogenase (LADH) with cyclohexanol as a substrate and yeast formate dehydrogenase (FDH) with formate as a substrate. On the basis of less precise previous measurements of these {sup 15}N isotope effects, the nicotinamide ring of NAD has been suggested to adopt a boat conformation with carbonium ion character at C-4 during hydride transfer. If this mechanism were valid, as N-1 becomes pyramidal an {sup 15}N isotope effect for the reaction catalyzed by LADH was measured. These values suggest that a significant {sup 15}N kinetic isotope effect is not associated with hydride transfer for LADH and FDH. Thus, in contrast with the deformation mechanism previously postulated, the pyridine ring of the nucleotide apparently remains planar during these dehydrogenase reactions.

Rotberg, N.S.; Cleland, W.W. (Univ. of Wisconsin, Madison (USA))

1991-04-23

218

Eastern oyster (Crassostrea virginica) ?15N as a bioindicator of nitrogen sources: Observations and modeling  

PubMed Central

Stable nitrogen isotopes (?15N) in bioindicators are increasingly employed to identify nitrogen sources in many ecosystems and biological characteristics of the eastern oyster (Crassostrea virginica) make it an appropriate species for this purpose. To assess nitrogen isotopic fractionation associated with assimilation and baseline variations in oyster mantle, gill, and muscle tissue ?15N, manipulative fieldwork in Chesapeake Bay and corresponding modeling exercises were conducted. This study (1) determined that five individuals represented an optimal sample size; (2) verified that ?15N in oysters from two locations converged after shared deployment to a new location reflecting a change in nitrogen sources; (3) identified required exposure time and temporal integration (four months for muscle, two to three months for gill and mantle); and (4) demonstrated seasonal ?15N increases in seston (summer) and oysters (winter). As bioindicators, oysters can be deployed for spatial interpolation of nitrogen sources, even in areas lacking extant populations.

Fertig, B.; Carruthers, T.J.B.; Dennison, W.C.; Fertig, E.J.; Altabet, M.A.

2013-01-01

219

Modeling the flow of 15N after a 15N pulse to study long-term N dynamics in a semiarid grassland.  

PubMed

Many aspects of nitrogen (N) cycling in terrestrial ecosystems remain poorly understood. Progress in studying N cycling has been hindered by a lack of effective measurements that integrate processes such as denitrification, competition for N between plants and microbes, and soil organic matter (SOM) decomposition over large time scales (years rather than hours or days). Here I show how long-term measurements of 15N in plants, microbes, and soil after a one-time addition of 15N ("labeled" N) can provide powerful information about long-term N dynamics in a semiarid grassland. I develop a simple dynamic model and show that labeled-N fractions in plant and microbial-N pools (expressed as a fraction of total N in each pool) can change long after 15N application (> or = 5 years). These 15N dynamics are closely tied to the turnover times of the different N pools. The model accurately simulated the labeled-N fractions in aboveground biomass measured annually during five years after addition of 15N to a semiarid grassland. I also tested the sensitivity of five different processes on labeled-N fractions in aboveground plant biomass. Changing plant/microbial competition for N had very little effect on the labeled-N fraction in aboveground biomass in the short and long-term. Changing microbial activity (N mineralization and immobilization), N loss, or N resorption/re-translocation by plants affected the labeled-N fraction in the short-term, but not in the long-term. Large long-term effects on the labeled-N fraction in aboveground biomass could only be established by changing the size of the active soil-N pool. Therefore, the significantly greater long-term decline in the labeled-N fraction in aboveground biomass observed under elevated CO2 in this grassland system could have resulted from an increased active soil-N pool under elevated CO2 (i.e., destabilization of soil organic matter that was relatively recalcitrant under ambient CO2 conditions). I conclude that short- and long-term labeled-N fractions in plant biomass after a 15N pulse are sensitive to processes such as N mineralization and immobilization, N loss, and soil organic matter (de-)stabilization. Modeling these fractions provides a useful tool to better understand N cycling in terrestrial ecosystems. PMID:19739379

Dijkstra, Feike A

2009-08-01

220

Free amino acid turnover in methanogens measured by 15N NMR spectroscopy.  

PubMed

Turnover of the nitrogen moiety from free amino acid pools in two thermophilic methanogens, Methanobacterium thermautotrophicum delta H and Methanococcus thermolithotrophicus SN1, has been monitored with 15N NMR spectroscopy. In cells growing exponentially on 15NH4Cl, glutamate was the major soluble 15N-labeled species in both organisms. When the Mb. thermoautotrophicum cells were harvested, washed, and resuspended into medium containing 14NH4Cl, the resonance for [15N]glutamate decreased with a half-life of 0.5 h. This is considerably faster than the turnover rate for the carbon side chain of glutamate (7 h) obtained when a 13CO2 pulse followed by a 12CO2 chase was incorporated into the 15N/14N-labeling experiment. Such behavior is consistent with recycling of the glutamate carbon skeleton via alpha-ketoglutarate after transamination reactions remove the 15N for biosynthesis of other amino acids, nucleic acids, etc. When the cells were in stationary phase, 15N turnover was considerably slower indicating that transaminase activity had also decreased. Mc. thermolithotrophicus has a much more fragile cell wall and easily lyses. To avoid cell loss in the 15N/14N experiment, 15NH+4 growth followed by 14NH4+ dilution was used. In this organism the glutamate-labeled nitrogen turns over quite rapidly (t1/2 approximately 9 min), at a rate comparable to that for the carbon skeleton (t1/2 approximately 10 min). Beta-Glutamate, the second major carbon and nitrogen pool in this organism, turns over its 15N label very slowly. Therefore, this beta-amino acid does not appear to serve as a nitrogen donor in Mc. thermolithotrophicus. PMID:2211697

Roberts, M F; Choi, B S; Robertson, D E; Lesage, S

1990-10-25

221

1 H, 13 C and 15 N chemical shift referencing in biomolecular NMR  

Microsoft Academic Search

A considerable degree of variability exists in the way that 1H, 13C and 15N chemical shifts are reported and referenced for biomolecules. In this article we explore some of the reasons for this situation and propose guidelines for future chemical shift referencing and for conversion from many common 1H, 13C and 15N chemical shift standards, now used in biomolecular NMR,

David S. Wishart; Colin G. Bigam; Jian Yao; Frits Abildgaard; H. Jane Dyson; Eric Oldfield; John L. Markley; Brian D. Sykes

1995-01-01

222

Low late Pliocene sedimentary \\\\delta15N from a 10 site survey  

Microsoft Academic Search

Comparison of sediment samples from 10 ODP sites in the Pacific, Atlantic and Indian Oceans reveals a widespread change in the \\\\delta15N of sedimentary organic matter between late Pliocene and Holocene times. Late Pliocene \\\\delta15N values from the Pacific, Indian and southwestern Atlantic are 2.3 \\\\permil lower than their modern counterparts while sites in the north and tropical Atlantic show

R. S. Robinson; P. A. Meyers

2001-01-01

223

Microwave spectrum of P 14N and P 15N: Spectroscopic constants and molecular structure  

Microsoft Academic Search

In the present work the J+1?J, with J=1–3, 6, 7, 10–16, rotational transitions of P14N and the J+1?J, with J=1, 2, 7, 8, 10–14, rotational transitions of P15N have been observed in the millimeter- and submillimeter-wave region. These measurements allowed us to improve the ground state rotational parameters of P14N as well as provide those of P15N for the first

Gabriele Cazzoli; Lino Cludi; Cristina Puzzarini

2006-01-01

224

15 N isotope dilution techniques to study soil nitrogen transformations and plant uptake  

Microsoft Academic Search

The use of15N as a tracer in soil\\/plant research is examined. The limitations of the so-called Ndff approach are discussed to show the need to consider not just the fate of the added label but also the path that was followed and the rate of the transformation. The development of15N isotope dilution techniques to determine gross rates of nitrogen transformation

D. Barraclough

1995-01-01

225

Recovery of 15 N from ammonium nitrate and algal biomass-amended soil  

Microsoft Academic Search

A greenhouse experiment was conducted to compare the effectiveness of blue-green algae (Anabaena flos aquae) produced in a simulated inorganic-wastewater medium and NH4NO3 as sources of N for bermudagrass (Cynodon dactylon L.) on a Decatur silt loam soil (clayey, kaolinitic, thermic Rhodic Paleudult).15N-labeled blue-green algae and15N-labeled NH4NO3 were used as N sources to supply up to 300 mg N per

K. R. Sistani; R. W. Taylor; R. D. Hauck; K. R. Kelley

1989-01-01

226

Rotations in ?-15N2 and ?-14N2: Magnetic resonance comparison  

NASA Astrophysics Data System (ADS)

Recent NMR experiments suggested that the rotations in the rotor solid ?-14N2 are different from those in ?-14N2, particularly at low temperatures. Specifically, the orientational average of P2(?), p?<(32?-1)>2, was determined to be | p |~=0.1 in 15N2, while it is known that | p |<~10-3 in 14N2. This would be a surprising isotope effect. We have reexamined this issue by using the quadrupole splitting of dilute 14N2 in a ?-15N2 host as a sensitive probe of p. We find | p |<~10-3, just as in pure ?-14N2. We argue that this value applies to both isotopes in our isotopic mixtures. The second moment of the 15N2 resonance agrees reasonably with the intermolecular part of the Van Vleck second moment, indicating again that p is small in ?-15N2. We find no evidence that the rotations in ?-15N2 differ fromthose in ?14N2. Some of the 14N2 linewidth in the isotopic mixtures arises from random-site occupation by the isotopes. Translational diffusion modulates these electric field gradients and causes a peak in T-12 as a function of temperature. The activation energy for diffusion is found to agree with a previous measurement in pure ?-15N2.

Doverspike, Montee A.; Conradi, Mark S.

1984-11-01

227

Trophic subsidies of Crassostrea gigas, Mytilus edulis and Crepidula fornicata in the Bay of Mont Saint Michel (France): A ? 13C and ? 15N investigation  

Microsoft Academic Search

This study focussed on the determination of the main trophic subsidies for three dominant filter feeding molluscs of the benthic community, namely, Crassostrea gigas (Thunberg), Mytilus edulis (L.) and Crepidula fornicata (L.), cultivated or naturally occurring in the Bay of Mont Michel (France). ?13C and ?15N values revealed that the diet of these filter feeders was primarily based on marine

Pascal Riera

2007-01-01

228

Acetylene inhibition of N2O reduction in laboratory soil and groundwater denitrification assays: evaluation by 15N tracer and 15N site preference of N2O  

NASA Astrophysics Data System (ADS)

The measurement of denitrification in soils and aquifers is still challenging and often enough associated with considerable experimental effort and high costs. Against this background, the acetylene inhibition technique (AIT) applied in laboratory soil and groundwater denitrification assays is by far the most effective approach. However, this method has been largely criticized, as it is susceptible to underestimate denitrification rates and adds an additional carbon source to the substrates to be investigated. Here we provide evidence that the AIT is not necessarily an inappropriate approach to measure denitrification, that its reliability depends on the drivers governing the process, and that the 15N site preference of N2O (SP) may serve as a tool to assess this reliability. Two laboratory batch experiments were conducted, where sandy aquifer material and a peat soil were incubated as slurries. We established (i) a standard anaerobic treatment by adding KNO3 (10 mg N L-1), (ii) an oxygen treatment by adding KNO3 and O2 (5 mg L-1), and (iii) a glucose treatment by adding KNO3 supplemented with glucose (200 mg C L-1). Both experiments were run under 10 % (v/v) acetylene atmosphere and as 15N tracer treatments using labeled K15NO3 (60 atom % 15N). In the case of the standard anaerobic treatments, we found a very good agreement of denitrification potential obtained by the AIT and 15N tracer methods. SP of N2O of the AIT samples from this treatment ranged between -4.8 and 2.6 ‰ which is indicative for N2O production during bacterial denitrification but not for N2O reduction to N2. In contrast, we observed substantial underestimation of denitrification by AIT for the glucose treatments compared to the 15N method, i.e. denitrification was underestimated by 36 % (sandy aquifer material) and 47 % (peat soil). SP of N2O of the AIT samples from this treatment ranged between 4.5 and 9.6 ‰, which suggests occurrence of bacterial N2O reduction. In the case of the oxygen treatments, we observed a very good agreement of denitrification potential obtained by the AIT and 15N tracer methods for the aquifer material, but a significant underestimation of 20 % in the AIT samples of the peat soil. The 15N site preference of N2O again mirrored this and ranged between -1.2 and -3.5 ‰ (aquifer material) and 5.5 and 11.0 (peat soil), respectively. We conclude that the AIT can act as a reliable method in laboratory soil and groundwater bacterial denitrification assays, but our results suggest that this relies on substrate types and incubation conditions. Additional measurements of SP have potential to assess AIT efficacy and can help to reduce parallel time-consuming and expensive 15N tracer experiments.

Weymann, Daniel; Well, Reinhard; Lewicka-Szczebak, Dominika; Lena, Rohe

2013-04-01

229

(15)N 2 Incorporation and metabolism in the lichen Peltigera aphthosa Willd.  

PubMed

The Nostoc in the cephalodia of the lichen Peltigera aphthosa Willd. fixed (15)N2 and the bulk of the nitrogen fixed was continuously transferred from it to its eukaryotic partners (a fungus and a green alga, Coccomyxa sp.). Kinetic studies carried out over the first 30 min, after exposure of isolated cephalodia to (15)N2, showed that highest initial (15)N2-labelling was into NH 4 (+) . After 12 min little further increase in the NH 4 (+) label occurred while that in the amide group of glutamine and in glutamate continued to increase. The (15)N-labelling of the amino group of glutamine and of aspartate increased more slowly, followed by an increase in the labelling of alanine. When total incorporation of (15)N-label was calculated, the overall pattern was found to be rather similar except that, throughout the experiment, the total (15)N incorporated into glutamate was about six times greater than that into the amide group of glutamine. Pulse chase experiments, in which (14)N2 was added to cephalodia previously exposed to (15)N2, showed that the NH 4 (+) pool rapidly became depleted of (15)N-label, followed by decreases in the labelling of glutamate, the amide group of glutamine and aspartate. The (15)N-labelling of alanine, however, continued to increase for a period. When isolated cephalodia were treated with L-methionine-SR-sulphoximine, an inhibitor of glutamine synthetase (EC 6.3.1.2), and azaserine, an inhibitor of glutamate synthase (EC 2.6.1.53), there was no detectable labelling in glutamine although the (15)N-labelling of glutamate increased unimpaired. On treating the cephalodia with amino-oxyacetate, an inhibitor of aminotransferase activity, the alanine pool decreased. Evidence was obtained that glutamine synthetase and glutamate synthase were located in the Nostoc, and that glutamate dehydrogenase (EC 1.4.1.4) and various amino-transferases were located in the cephalodial fungus. Possible implications of these findings are discussed. PMID:24301158

Rai, A N; Rowell, P; Stewart, W D

1981-10-01

230

Using PLFA Biomarkers and Natural Abundance Stable and Radiocarbon Isotopes to Characterize the Microbial Ecology and Metabolism of Methane Cycling  

NASA Astrophysics Data System (ADS)

Methane generated in the subsurface is a major source of atmospheric CH4, but its release is mitigated by CH4-oxidizing bacteria (methanotrophs). Therefore, it is important to understand the ecology of methanotroph communities in various environments. Phospholipid fatty acid (PLFA) analyses are a particularly useful method for characterizing these communities for two reasons: (1) Many type I and II methanotrophs produce specific PLFA biomarkers that can be used to estimate their populations, and (2) because CH4 is often very depleted in 13C and sometimes 14C, natural abundance ?13CPLFA and ?14CPLFA values can be used to trace the flow of CH4- derived carbon through microbial ecosystems. We used these tools to evaluate the role of methanotrophs in carbon flow in three different environments: (1) a soil column overlying a coal bed methane (CBM) seep in southwest CO, and pristine, oligotrophic groundwaters within (2) sedimentary and (3) granitic host rocks in Japan. In the soil column impacted by CBM seepage, concentrations of the biomarker PLFAs for type I (16:1?8cis) and type II (18:1?8cis) methanotrophs were as high as 13 and 18 nmoles (g dry soil)-1, respectively. Depth profiles of methanotroph PLFA concentrations varied over different sampling dates indicating dynamic populations. ?13CPLFA values of the CBM soils (-25.1 to - 66.9‰) were substantially more negative than those for the control soil (-14.5 to -32.5‰) indicating that CBM is an important carbon source for the CBM-impacted soil microbial community. ?14CPLFA values (-351 to -936‰) indicate the importance of 14C-dead CBM as a carbon source to the microbial communities, contributing 32 to 66% of total carbon in PLFA structures isolated from shallow soils and 67 to 97% for those isolated from deeper soils. The biomarker for type II methanotrophs, comprised 3 and 18% of total PLFAs in sedimentary and granitic groundwaters, respectively. The ?14C values determined for type II methanotroph PLFAs in the sedimentary (- 861‰) and granite (-867‰) waters were very similar to the ?14C values of dissolved inorganic carbon (DIC) in each water (ca -850‰) suggesting that type II methanotrophs ultimately derive all of their carbon from DIC. In contrast, ?13C values of type II PLFAs in the sedimentary (- 93‰) and granite (-60‰) waters indicate that these organisms use different carbon assimilation schemes in each environment. These studies show the utility of PLFA biomarkers and ?13CPLFA and ?14CPLFA values to characterize the in situ metabolisms of methanotrophic bacteria and overall CH4 recycling in diverse environments.

Mills, C. T.; Mandernack, K. W.; Slater, G. F.; Dias, R. F.

2008-12-01

231

N-15 NMR spectra of naturally abundant nitrogen in soil and aquatic natural organic matter samples of the International Humic Substances Society  

SciTech Connect

The naturally abundant nitrogen in soil and aquatic NOM samples from the International Humic Substances Society has been characterized by solid state CP/MAS ¹?N NMR. Soil samples include humic and fulvic acids from the Elliot soil, Minnesota Waskish peat and Florida Pahokee peat, as well as the Summit Hill soil humic acid and the Leonardite humic acid. Aquatic samples include Suwannee River humic, fulvic and reverse osmosis isolates, Nordic humic and fulvic acids and Pony Lake fulvic acid. Additionally, Nordic and Suwannee River XAD-4 acids and Suwannee River hydrophobic neutral fractions were analyzed. Similar to literature reports, amide/aminoquinone nitrogens comprised the major peaks in the solid state spectra of the soil humic and fulvic acids, along with heterocyclic and amino sugar/terminal amino acid nitrogens. Spectra of aquatic samples, including the XAD-4 acids, contain resolved heterocyclic nitrogen peaks in addition to the amide nitrogens. The spectrum of the nitrogen enriched, microbially derived Pony Lake, Antarctica fulvic acid, appeared to contain resonances in the region of pyrazine, imine and/or pyridine nitrogens, which have not been observed previously in soil or aquatic humic substances by ¹?N NMR. Liquid state ¹?N NMR experiments were also recorded on the Elliot soil humic acid and Pony Lake fulvic acid, both to examine the feasibility of the techniques, and to determine whether improvements in resolution over the solid state could be realized. For both samples, polarization transfer (DEPT) and indirect detection (¹H–¹?N gHSQC) spectra revealed greater resolution among nitrogens directly bonded to protons. The amide/aminoquinone nitrogens could also be observed by direct detection experiments.

Thorn, Kevin A.; Cox, Larry G.

2009-02-28

232

Distribution of 15N in amino acids during 15N-leucine infusion: impact on the estimation of endogenous flows in dairy cows.  

PubMed

The distribution of (15)N in AA during [(15)N]Leu infusion and its impact on the estimation of endogenous nitrogen (EN) flows in dairy cows was evaluated in 4 lactating cows equipped with ruminal, duodenal (n = 4), and ileal (n = 2) cannulae fed a silage-based diet during a 35-d experimental period. To label EN, starting on d 27, an infusion of L-[(15)N]Leu (0.45 mmol/h) was performed for 200 h. Samples of feed, duodenal and ileal digesta, feces, blood, urine, and mucosa of the rumen and duodenum were taken at 0900, 1100, 1300, and 1500 h on d 34 and at 0800, 1000, 1200, and 1400 h on d 35. The enrichment and fluxes of total N and individual AA were determined and used to calculate the EN flows at the duodenum, ileum, and in the feces. Based on the concept that EN comprises desquamation and secretions, EN flows were estimated, using as representative of the enrichment of EN only the enrichment of the gut mucosa (upper limit) or the average of the mucosa and the export protein enrichment (assumed to have a similar enrichment to casein; lower limit). Estimations of duodenal and fecal EN flows using the isotope dilution of (15)N-total and (15)N-Leu were not different and EN was an important fraction of duodenal and fecal flows, representing 14 to 30% of the duodenal flow and 18 to 31% of the fecal flow, depending on the dilution method used. The total EN flow at the duodenum is present in approximately equal proportions as either free EN or EN incorporated into bacterial protein. Ileal EN flow was 18% greater than the fecal EN flow. Using the combination of the gut and export protein, the duodenal and fecal EN flows estimated with the isotopic dilution of Leu vs. other labeled AA were less different than when estimated using the enrichment of gut mucosa alone. The current approaches have highlighted that present prediction schemes probably underestimate EN flows at the duodenum and, in consequence, overestimate net protein and AA supply. Refinement of the procedures may allow direct and accurate estimation of metabolic fecal protein, an important component of the so-called maintenance requirement of dairy cows. PMID:18565929

Lapierre, H; Ouellet, D R; Berthiaume, R; Martineau, R; Holtrop, G; Lobley, G E

2008-07-01

233

Sewage derive [sup 15]N in the Baltic traced in fucus  

SciTech Connect

Himmerfjarden, a fjord-like bay on the eastern shore of the Baltic, receives treated sewage from 250,000 inhabitants. Because the inorganic N in the effluent is enriched in [sup 15]N through denitrification, nitrification, and ammonia volatilization, an analysis of the distribution of [sup 15]N in the Bay tells how far from the source the sewage nitrogen moves. The attached macroalga Fucus vesiculosus was collected in early May from rocky shore at 0-0.5 m depth and the [sup 15]N content of the tips of the fronds analyzed. This N represents uptake and storage during the previous six months and growth during March and April. The [delta][sup 15]N was uniformly high (11-13[per thousand]) in the main body of the Bay within 15 km from the sewage source. Beyond 15 km values decreased with distance to a low of 4.6[per thousand] at 35 km, where the Bay ends and the coastal waters begin. Using the 11-13 and 4.6[per thousand] as endmembers, the percentage of sewage N making up the Fucus at any point may be calculated. The [delta][sub 15]N of particulate organic matter in the offshore Baltic waters was around 0[per thousand] and Fucus had an [delta][sup 15]N about 1.5[per thousand] higher than the POM. From this and other evidence we conclude that there is a belt of coastal water with an elevated [delta][sup 15]N lying along the east coast of the Baltic. This presumably derives from sewage and perhaps from agriculture and is potentially of use as a tracer of coastal zone/pelagic zone interactions.

Hobbie, J.E.; Fry, B. (The Ecosystems Center, Woods Hole, MA (United States)); Larsson, U.; Elmgren, R. (Univ. of Sotckholm (Sweden))

1990-01-09

234

Estimating modal abundances from the spectra of natural and laboratory pyroxene mixtures using the modified Gaussian model  

NASA Astrophysics Data System (ADS)

The modified Gaussian model (MGM) is used to explore spectra of samples containing multiple pyroxene components as a function of modal abundance. The MGM allows spectra to be analyzed directly, without the use of actual or assumed end-member spectra and therefore holds great promise for remote applications. A series of mass fraction mixtures created from several different particle size fractions are analyzed with the MGM to quantify the properties of pyroxene mixtures as a function of both modal abundance and grain size. Band centers, band widths, and relative band strengths of absorptions from individual pyroxenes in mixture spectra are found to be largely independent of particle size. Spectral properties of both zoned and exsolved pyroxene components are resolved in exsolved samples using the MGM, and modal abundances are accurately estimated to within 5-10 percent without predetermined knowledge of the end-member spectra.

Sunshine, J. M.; Pieters, C. M.

1993-05-01

235

Estimating modal abundances from the spectra of natural and laboratory pyroxene mixtures using the modified Gaussian model  

NASA Technical Reports Server (NTRS)

The modified Gaussian model (MGM) is used to explore spectra of samples containing multiple pyroxene components as a function of modal abundance. The MGM allows spectra to be analyzed directly, without the use of actual or assumed end-member spectra and therefore holds great promise for remote applications. A series of mass fraction mixtures created from several different particle size fractions are analyzed with the MGM to quantify the properties of pyroxene mixtures as a function of both modal abundance and grain size. Band centers, band widths, and relative band strengths of absorptions from individual pyroxenes in mixture spectra are found to be largely independent of particle size. Spectral properties of both zoned and exsolved pyroxene components are resolved in exsolved samples using the MGM, and modal abundances are accurately estimated to within 5-10 percent without predetermined knowledge of the end-member spectra.

Sunshine, Jessica M.; Pieters, Carle M.

1993-01-01

236

Impact of a nucleopolyhedrovirus bioinsecticide and selected synthetic insecticides on the abundance of insect natural enemies on maize in southern Mexico.  

PubMed

The impact of commonly used organophosphate (chlorpyrifos, methamidophos), carbamate (carbaryl), and pyrethroid (cypermethrin) insecticides on insect natural enemies was compared with that of a nucleopolyhedrovirus (Baculoviridae) of Spodoptera frugiperda (J. E. Smith) (Lepidoptera Noctuidae) in maize grown in southern Mexico. Analyses of the SELECTV and Koppert Side Effects (IOBC) databases on the impact of synthetic insecticides on arthropod natural enemies were used to predict approximately 75-90% natural enemy mortality after application, whereas the bioinsecticide was predicted to have no effect. Three field trails were performed in mid- and late-whorl stage maize planted during the growing season in Chiapas State, Mexico. Synthetic insecticides were applied at product label recommended rates using a manual knapsack sprayer fitted with a cone nozzle. The biological pesticide was applied at a rate of 3 x 10(12) occlusion bodies (OBs)/ha using identical equipment. Pesticide impacts on arthropods on maize plants were quantified at intervals between 1 and 22 d postapplication. The biological insecticide based on S. frugiperda nucleopolyhedrovirus had no adverse effect on insect natural enemies or other nontarget insect populations. Applications of the carbamate, pyrethroid, and organophosphate insecticides all resulted in reduced abundance of insect natural enemies, but for a relatively short period (8-15 d). Pesticide applications made to late-whorl stage maize resulted in lesser reductions in natural enemy populations than applications made at the mid-whorl stage, probably because of a greater abundance of physical refuges and reduced spray penetration of late-whorl maize. PMID:12852601

Armenta, R; Martínez, A M; Chapman, J W; Magallanes, R; Goulson, D; Caballero, P; Cave, R D; Cisneros, J; Valle, J; Castillejos, V; Penagos, D I; García, L F; Williams, T

2003-06-01

237

Highly 15N-enriched chondritic clasts in the CB/CH-like meteorite Isheyevo  

NASA Astrophysics Data System (ADS)

The metal-rich carbonaceous chondrites (CB and CH) have the highest whole-rock 15N-enrichments (? 15N up to 1500‰) among planetary materials. They are also characterized by the absence of interchondrule fine-grained matrix. The only fine-grained material is present as lithic clasts, which experienced extensive aqueous alteration in contrast to the surrounding high-temperature components (chondrules, refractory inclusions, metal grains). Hence, the clasts are foreign objects that were incorporated at a late stage into the final parent body of Isheyevo. Their origin is poorly constrained. Based on mineralogy, petrography, and thermal processing of the aromatic carbonaceous component, different types of clasts have been previously identified in the CB/CH-like chondrite Isheyevo. Here, we focus on the rare lithic clasts characterized by the presence of anhydrous silicates (chondrules, chondrule fragments, and CAIs). Their mineralogy and oxygen isotopic compositions reveal them to be micro-chondrules, fragments of chondrules, and refractory inclusions related to those in the Isheyevo host, suggesting accretion in the same region. In contrast to previously studied IDPs or primitive chondritic matrices, the fine-grained material in the clasts we studied is highly and rather uniformly enriched in heavy nitrogen, with bulk ? 15N values ranging between 1000‰ and 1300‰. It is also characterized by the presence of numerous 15N hotspots (? 15N ranging from 1400‰ to 4000‰). No bulk (?D <-240‰) or localized deuterium enrichments were observed. These clasts have the highest bulk enrichment in heavy nitrogen measured to date in a fine-grained material. They represent a unique material, of asteroidal or cometary origin, in our collection of cosmomaterials. We show that they were 15N-enriched before their incorporation in the final parent body of Isheyevo. They experienced an extensive aqueous alteration that most likely played a role in redistributing 15N over the whole fine-grained material and may have significantly modified its initial hydrogen isotopic composition. Based on a review of isotopic fractionation models, we conclude that the nitrogen isotopic fractionation process, its timing, and its location are still poorly constrained. The 15N-rich clasts may represent the surviving original carrier of the 15N anomaly in Isheyevo whole-rock.

Bonal, L.; Huss, G. R.; Krot, A. N.; Nagashima, K.; Ishii, H. A.; Bradley, J. P.

2010-11-01

238

Low-level nitrate export from confined dairy farming detected in North Carolina streams using ? 15 N  

Microsoft Academic Search

Animal waste-produced nitrate in streams can be detected with natural abundance nitrogen isotopes even when stream nitrate concentrations are low and derive predominantly from natural soil nitrate sources. The objective of this limited study was to demonstrate the utility of such an approach with a minimal number of samples and minimal supporting data. These constraints are important in terms of

Jonathan D. Karr; William J. Showers; Gregory D. Jennings

2003-01-01

239

[The determination of a gross utilization of 15N-lysine in laboratory rats. 1. Experiment with normal intestinal flora (without antibiotic supplement)].  

PubMed

Wistar rats of a live weight of about 100 g were divided into 14 groups (5 animals/group). The rations given supplied the animals with 75%, 100% and 125% lysine, which brought about a moderate growth of the animals of approximately 2 g/animal and day achieved by limited feeding. The 3 lysine levels mentioned could be achieved by lysine supplements (L-lysine-HCl) for the following rations: barley (B), wheat (W), and wheat gluten (WG). For isolated soybean protein (assay protein) (S) the lysine levels 100% and 125% and for soybean meal (SM) the levels 116% and 125% could only be achieved. A control group with whole egg ration (W) (with its natural lysine content of 125% of the requirement) were also tested as comparison. During the 10-day period of the main experiment all 14 rations were supplemented with 0.5 g 15N-lysine (alpha amino group, 95% labelled with 15N). The N balance could only be significantly improved by lysine supplements in the rations B, W and SM with the lysine level of 125%. The biologic value of the protein sources was in rations B and WG also significantly improved by the highest lysine supplement. 15N excess (15N') from the deaminated 15N lysine was excreted with diet B rich in crude fibre mainly in faeces (more than 15% of the intake) and only about 10% in urine. With the diets without native crude fibre the excretion quota changed in favour of urine. The following 15N' amounts in per cent of 15N' intake from lysine were excreted in urine and faeces: B 75 = 31.3, B 100 = 30.9, B 125 = 28.0, W 75 = 24.3, W 100 = 32.2, W 125 = 32.6, GW 75 = 18.3, WG 100 = 24.2, WG 125 = 28.1, S 100 = 39.4, S 125 = 50.4, SM 116 = 34.9, SM 125 = 32.9, W 125 = 19.1. 15N excretion in urine and faeces increased in comparable relations in 6 cases of lysine increase levels only. Gross utilization of lysine can only conditionally be quantified by 15N labelled lysine supplement. PMID:1665059

Bergner, H; Schwandt, H

1991-10-01

240

Natural-Abundance Carbon13 FourierTransform Nuclear Magnetic Resonance Spectra and Spin Lattice Relaxation Times of Unfractionated Yeast Transfer-RNA  

Microsoft Academic Search

High-resolution Fourier-transform nuclear magnetic resonance at 15.18 MHz was used to observe the proton-decoupled natural-abundance 13C spectra of aqueous unfractionated tRNA from baker's yeast in the presence of Mg+2 (8 ions per tRNA molecule), as a function of temperature in the range of 27-82 degrees C. The spectrum of thermally denatured tRNA at 82 degrees C showed numerous sharp resonances,

Richard A. Komoroski; Adam Allerhand

1972-01-01

241

Effects of genetically modified potatoes with increased zeaxanthin content on the abundance and diversity of rhizobacteria with in vitro antagonistic activity do not exceed natural variability among cultivars  

Microsoft Academic Search

To assess potential effects of genetically modified (GM) potatoes on the abundance and diversity of rhizobacteria with in\\u000a vitro antagonistic activity in relation to natural variability among cultivars, two GM potato lines accumulating the carotenoid\\u000a zeaxanthin in their tubers, the parental cultivar and four additional commercial cultivars were planted at two field sites\\u000a in Germany. Rhizosphere samples were taken at

Nicole Weinert; Remo Meincke; Christine Gottwald; Viviane Radl; Xia Dong; Michael Schloter; Gabriele Berg; Kornelia Smalla

2010-01-01

242

Sources of nitrate in the Arno River waters: Constraints from ?? 15N and ??18O  

USGS Publications Warehouse

Running waters in anthropogenically affected areas are susceptible to nitrate contamination. Source identification is a fundamental step for the development of effective remediation. Previous studies pointed to pollution by nitrogen-bearing contaminants in the Arno Basin. In this paper, eleven surface water samples have been analysed for main and trace components and 15N/14N and 18O/16O ratios, with the aim of identifying for the first time the origin of nitrate in the Arno River Basin so that further investigations can appropriately be designed. ?? 18O(NO3) and ??15N(NO3) values have allowed to hypothesise the main sources of nitrate, as follows: i) mineralized fertilizer, ii) soil-organic nitrogen, iii) manure and septic waste. The anomalously high ??15N and ??18O values in the Chiana (??15N=24.9??? and ??18O= 15.5???) and Usciana tributaries (??15N=30.1??? and ??18O=7.2???) show a low probability of belonging to the same population as that of the other samples and can be related to denitrification process of nitrate from animal waste/sewage and/or an industrial process (e.g. tanneries).

Nisi, B.; Vaselli, O.; Buccianti, A.; Silva, S. R.

2005-01-01

243

DETERMINATES OF CANOPY EPIPHYTE ABUNDANCE IN A PRIMARY LOWER MONTANE CLOUD FOREST IN CLOUDBRIDGE NATURE RESERVE, COSTA RICA  

Microsoft Academic Search

Epiphytes play an integral role in neotropical rainforest ecosystems. Thus, it is important to understand factors that contribute to the presence or absence of epiphytic growth. The purpose of this study was to determine correlations among height, diameter at breast height (dbh), aspect, slope, and tree species with respect to epiphyte abundance. We sampled 720 trees within a one-hectare study

Debbie L. Valliere; Dario A. Elliott

244

Estimating Modal Abundances From the Spectra of Natural and Laboratory Pyroxene Mixtures Using the Modified Gaussian Model  

Microsoft Academic Search

Spectra of samples containing multiple pyroxene components are explored as a function of modal abundance using the modified Gaussian model (MGM). The MGM, unlike other approaches, allows spectra to be analyzed directly, without the use of actual or assumed end-member spectra and therefore holds great potential for remote applications. Quantitative understanding of the spectral characteristics of lithologies which include mixtures

Jessica M. Sunshine; Carlé M. Pieters

1993-01-01

245

Accurate measurement of 15 N– 13 C residual dipolar couplings in nucleic acids  

Microsoft Academic Search

New 3D HCN quantitative J (QJ) pulse schemes are presented for the precise and accurate measurement of one-bond 15N1\\/9–13C1', 15N1\\/9–13C6\\/8, and 15N1\\/9–13C2\\/4 residual dipolar couplings (RDCs) in weakly aligned nucleic acids. The methods employ 1H–13C multiple quantum (MQ) coherence or TROSY-type pulse sequences for optimal resolution and sensitivity. RDCs are obtained from the intensity ratio of H1'–C1'–N1\\/9 (MQ-HCN-QJ) or H6\\/8–C6\\/8–N1\\/9

Christopher P. Jaroniec; Jérôme Boisbouvier; Izabela Tworowska; Edward P. Nikonowicz; Ad Bax

2005-01-01

246

3D 15N/15N/1H chemical shift correlation experiment utilizing an RFDR-based 1H/1H mixing period at 100 kHz MAS  

NASA Astrophysics Data System (ADS)

Homonuclear correlation NMR experiments are commonly used in the high-resolution structural studies of proteins. While 13C/13C chemical shift correlation experiments utilizing dipolar recoupling techniques are fully utilized under MAS, correlation of the chemical shifts of 15N nuclei in proteins has been a challenge. Previous studies have shown that the negligible 15N-15N dipolar coupling in peptides or proteins necessitates the use of a very long mixing time (typically several seconds) for effective spin diffusion to occur and considerably slows down a 15N/15N correlation experiment. In this study, we show that the use of mixing proton magnetization, instead of 15N, via the recoupled 1H-1H dipolar couplings enable faster 15N/15N correlation. In addition, the use of proton-detection under ultrafast MAS overcomes the sensitivity loss due to multiple magnetization transfer (between 1H and 15N nuclei) steps. In fact, less than 300 nL (?1.1 micromole quantity) sample is sufficient to acquire the 3D spectrum within 5 h. Our results also demonstrate that a 3D 15N/15N/1H experiment can render higher resolution spectra that will be useful in the structural studies of proteins at ultrafast MAS frequencies. 3D 15N/15N/1H and 2D radio frequency-driven dipolar recoupling (RFDR)-based 1H/1H experimental results obtained from a powder sample of N-acetyla-L-15N-valyl-L-15N-leucine at 70 and 100 kHz MAS frequencies are presented.

Nishiyama, Yusuke; Malon, Michal; Ishii, Yuji; Ramamoorthy, Ayyalusamy

2014-07-01

247

3D (15)N/(15)N/(1)H chemical shift correlation experiment utilizing an RFDR-based (1)H/(1)H mixing period at 100kHz MAS.  

PubMed

Homonuclear correlation NMR experiments are commonly used in the high-resolution structural studies of proteins. While (13)C/(13)C chemical shift correlation experiments utilizing dipolar recoupling techniques are fully utilized under MAS, correlation of the chemical shifts of (15)N nuclei in proteins has been a challenge. Previous studies have shown that the negligible (15)N-(15)N dipolar coupling in peptides or proteins necessitates the use of a very long mixing time (typically several seconds) for effective spin diffusion to occur and considerably slows down a (15)N/(15)N correlation experiment. In this study, we show that the use of mixing proton magnetization, instead of (15)N, via the recoupled (1)H-(1)H dipolar couplings enable faster (15)N/(15)N correlation. In addition, the use of proton-detection under ultrafast MAS overcomes the sensitivity loss due to multiple magnetization transfer (between (1)H and (15)N nuclei) steps. In fact, less than 300nL (?1.1micromole quantity) sample is sufficient to acquire the 3D spectrum within 5h. Our results also demonstrate that a 3D (15)N/(15)N/(1)H experiment can render higher resolution spectra that will be useful in the structural studies of proteins at ultrafast MAS frequencies. 3D (15)N/(15)N/(1)H and 2D radio frequency-driven dipolar recoupling (RFDR)-based (1)H/(1)H experimental results obtained from a powder sample of N-acetyla-l-(15)N-valyl-l-(15)N-leucine at 70 and 100kHz MAS frequencies are presented. PMID:24801998

Nishiyama, Yusuke; Malon, Michal; Ishii, Yuji; Ramamoorthy, Ayyalusamy

2014-07-01

248

Nitrate removal in two relict oxbow urban wetlands: a 15N mass-balance approach  

NASA Astrophysics Data System (ADS)

A mass-balance approach was used to directly determine the flow of 15NO3- to plants, algae, and sediments,with unaccounted for 15N assumed to be denitrified. During the summer, plant and algal uptake accounted for 42%, of the added 15NO3 - in oxbow 1, less than 1% remained in the water column and 57% was unaccounted for. In oxbow 2 during the summer, plant and algal uptake accounted for 63% of the added 15NO3 -, with 1% remaining in the water column and 38% unaccounted for. During the early spring, plant and algal uptake were much lower in both oxbows, ranging from 0.05 to 13.3% of the 15N added, with 97 and 87% was unaccounted for in oxbow 1 and 2, respectively. The amount of unaccounted for 15N was equivalent to estimated areal denitrification rates of 12 and 6 mg N m-2 d-1 in the summer and 78 and 15 mg N m-2 d-1 in the spring, in oxbow 1 and oxbow 2, respectively. However, the uncertainty of these estimates is high as it was difficult to detect accumulation of 15N in the sediments which could have accounted for a very large percentage of the added 15N. Our results suggest that the two relict oxbow wetlands are sinks for NO3 - during both summer and spring. Plane view of Ox1 (A) and Ox2 (B) wetlands with closed contour intervals (color scale) and surrounding stream and upland elevations (labeled in black) located at Minebank Run, near Glen Arms, MD. 15N enrichment (atom %) of measured N pools prior to (Day 0) and after (Day 5) the end of the experiment in July 2009 and April 2010 for Ox1 and Ox2. Values are mean atom % (n = 2 algae, macrophytes and sediment; n = 6 for water samples).

Harrison, M. D.; Groffman, P. M.; Mayer, P. M.; Kaushal, S.

2012-12-01

249

Comparison of pollinators and natural enemies: a meta-analysis of landscape and local effects on abundance and richness in crops.  

PubMed

To manage agroecosystems for multiple ecosystem services, we need to know whether the management of one service has positive, negative, or no effects on other services. We do not yet have data on the interactions between pollination and pest-control services. However, we do have data on the distributions of pollinators and natural enemies in agroecosystems. Therefore, we compared these two groups of ecosystem service providers, to see if the management of farms and agricultural landscapes might have similar effects on the abundance and richness of both. In a meta-analysis, we compared 46 studies that sampled bees, predatory beetles, parasitic wasps, and spiders in fields, orchards, or vineyards of food crops. These studies used the proximity or proportion of non-crop or natural habitats in the landscapes surrounding these crops (a measure of landscape complexity), or the proximity or diversity of non-crop plants in the margins of these crops (a measure of local complexity), to explain the abundance or richness of these beneficial arthropods. Compositional complexity at both landscape and local scales had positive effects on both pollinators and natural enemies, but different effects on different taxa. Effects on bees and spiders were significantly positive, but effects on parasitoids and predatory beetles (mostly Carabidae and Staphylinidae) were inconclusive. Landscape complexity had significantly stronger effects on bees than it did on predatory beetles and significantly stronger effects in non-woody rather than in woody crops. Effects on richness were significantly stronger than effects on abundance, but possibly only for spiders. This abundance-richness difference might be caused by differences between generalists and specialists, or between arthropods that depend on non-crop habitats (ecotone species and dispersers) and those that do not (cultural species). We call this the 'specialist-generalist' or 'cultural difference' mechanism. If complexity has stronger effects on richness than abundance, it might have stronger effects on the stability than the magnitude of these arthropod-mediated ecosystem services. We conclude that some pollinators and natural enemies seem to have compatible responses to complexity, and it might be possible to manage agroecosystems for the benefit of both. However, too few studies have compared the two, and so we cannot yet conclude that there are no negative interactions between pollinators and natural enemies, and no trade-offs between pollination and pest-control services. Therefore, we suggest a framework for future research to bridge these gaps in our knowledge. PMID:23578337

Shackelford, Gorm; Steward, Peter R; Benton, Tim G; Kunin, William E; Potts, Simon G; Biesmeijer, Jacobus C; Sait, Steven M

2013-11-01

250

Accurate proteome-wide protein quantification from high-resolution 15N mass spectra  

PubMed Central

In quantitative mass spectrometry-based proteomics, the metabolic incorporation of a single source of 15N-labeled nitrogen has many advantages over using stable isotope-labeled amino acids. However, the lack of a robust computational framework for analyzing the resulting spectra has impeded wide use of this approach. We have addressed this challenge by introducing a new computational methodology for analyzing 15N spectra in which quantification is integrated with identification. Application of this method to an Escherichia coli growth transition reveals significant improvement in quantification accuracy over previous methods.

2011-01-01

251

Oak loss increases foliar nitrogen, ?(15)N and growth rates of Betula lenta in a northern temperate deciduous forest.  

PubMed

Oak forests dominate much of the eastern USA, but their future is uncertain due to a number of threats and widespread failure of oak regeneration. A sudden loss of oaks (Quercus spp.) could be accompanied by major changes in forest nitrogen (N) cycles with important implications for plant nutrient uptake and tree species composition. In this study, we measured the changes in N use and growth rates of black birch trees (Betula lenta L.) following oak girdling at the Black Rock Forest in southeastern New York, USA. Data were collected from nine experimental plots composed of three treatments: 100% oaks girdled (OG), 50% oaks girdled (O50) and control (C). Foliar N concentration and foliar (15)N abundance increased significantly in the oak-girdled plots relative to the control, indicating that the loss of oaks significantly altered N cycling dynamics. As mineralization and nitrification rates increase following oak loss, black birch trees increase N absorption as indicated by higher foliar N content and increased growth rates. Foliar N concentration increased by 15.5% in the O50 and 30.6% in the OG plots relative to the control, while O50 and OG plots were enriched in (15)N by 1.08‰ and 3.33‰, respectively (P?

Falxa-Raymond, Nancy; Patterson, Angelica E; Schuster, William S F; Griffin, Kevin L

2012-09-01

252

Complexity of the food web structure of the Ascophyllum nodosum zone evidenced by a ?13C and ?15N study  

NASA Astrophysics Data System (ADS)

Rocky shores dominated by canopy-forming macroalgae are characterized by complex communities making it difficult to assess whether the most abundant primary producers are at the base of the food web. This difficulty is exacerbated by the seasonal- and regional-scale variations of environmental and biotic factors that can affect the main trophic pathways. The food web structure of the Ascophyllum nodosum zone was studied during three seasons and at two sites separated by several 100s of kilometers by measuring the ?13C and ?15N of the major food sources and the dominant consumers of the zone. Despite the variability in isotopic compositions, both sites underwent similar significant seasonal variations. The main primary producers of the zone, A.nodosum, Fucus vesiculosus and Fucus serratus, were not at the base of the main trophic pathway but part of the diverse number of basal resources supporting the food web. The use of community-wide metric indices allowed further defining the food web structure of the A. nodosum zone as one characterized by trophic redundancy and numerous major trophic pathways. Indeed, grazers were dominated by generalists, filter-feeders utilized both planktonic and benthic organic matter, and predators displayed a high degree of omnivory. The range of values in ?15N showed a high spatiotemporal variability within and an important overlap between trophic groups. This prevented establishing distinctive trophic levels and further emphasized the complexity of the food web structure. The spatiotemporal stability of the relative isotopic composition of the dominant consumers within trophic groups and the low variability of the community-wide indices suggested a stability of the food web structure of the A.nodosum zone at a regional scale.

Golléty, Claire; Riera, Pascal; Davoult, Dominique

2010-10-01

253

Determination of the mutual orientation of the 15N and 13C NMR chemical shift tensors of 13- 15N double labeled model peptides for silk fibroin from the dipolar-coupled powder patterns  

NASA Astrophysics Data System (ADS)

The 15N and 13C chemical shift tensors, and the orientation of the principal axis system relative to the molecular symmetry axes were determined for 15N and 13C carbonyl carbon sites of 13C? 15N double labeled model peptides for Bombyx mori silk fibroin, that is, Boc-[1- 13C]Ala[ 15N]Gly-OMe, Boc-[1- 13C]Ala[ 15N]GlyAlaGly-OPac, Boc-AlaGly[1- 13C]Ala[ 15N]GlyAlaGly-OPac, Boc-[1- 13C]Gly[ 15N]AlaGlyAla-OPac, Boc-GlyAla[1- 13C]Gly[ 15N]AlaGlyAla-OPac and Boc-[1- 13C]Gly[ 15N]ValGlyAla-OPac, where Boc is t-butoxycarbonyl, OMe is methyl ester, OPac is phenacyl ester, Ala is alanine, Gly is glycine and Val is valine. From the comparisons of the 15N chemical shift tensors and the orientations of the principal axis system relative to the molecular symmetry axes among three compounds having [1- 13C]Ala[ 15N]Gly units, it is concluded that the intermolecular interactions such as hydrogen bonding are different between Boc-[1- 13C]Ala[ 15N]Gly-OMe and two compounds, Boc-[1- 13C]Ala[ 15N]GlyAlaGly-OPac and Boc-AlaGly[1- 13C]Ala[ 15N]GlyAlaGly-OPac although the latter two compounds have similar structures. A similar conclusion has also been obtained from the 13C chemical shift tensors of these compounds.

Asakura, Tetsuo; Yamazaki, Yasunobu; Seng, Koo Wey; Demura, Makoto

1998-05-01

254

The loss of organic nitrogen during marine primary production may be significantly overestimated when using 15N substrates  

PubMed Central

Field studies indicate that natural phytoplankton populations may release very significant amounts (20 to 40%) of newly assimilated dissolved inorganic nitrogen (DIN) as dissolved organic nitrogen (DON). In laboratory cultures, however, it is usually possible to account for at least 90% of nitrogen added to the system as DIN plus cell nitrogen. Here we show that the bulk of the missing nitrogen may be accounted for as dissolved free and dissolved combined amino acids. In cultures (which usually have a biomass density at least an order of magnitude greater than is present in offshore waters), the contribution of DON to system nitrogen thus appears to be minor. It is proposed that this difference may be explained if the levels of DON represent equilibrium between release–leakage and transport back into the algae. It is demonstrated, using a dynamic model of algal nitrogen physiology, that this mechanism can explain both laboratory and field observations. Simulations of incubations with DI15N reproduce the reported levels of loss in field incubations. However, because of isotope disequilibria between system components the 15N protocol may significantly overestimate the net loss of nitrogen from the algal cells. The arguments apply equally to studies of bacterial production of DON and to questions concerning the release of other dissolved organics by healthy phytoplankton. The significance of dynamic equilibria between the organisms and the medium may be missed in laboratory studies conducted with high biomass cultures.

Flynn, K. J.; Berry, L. S.

1999-01-01

255

Internal motion time scales of a small, highly stable and disulfide-rich protein: a 15N, 13C NMR and molecular dynamics study.  

PubMed

Motions of the backbone C alpha H alpha and threonine C beta H beta bonds of toxin alpha were investigated using natural abundance 13C NMR and molecular dynamics. Measurement of the 13C longitudinal and transverse relaxation rates employed ACCORDION techniques together with coherence selection by pulsed field gradients and sensitivity enhancement through the use of preservation of equivalent pathway, thus allowing a considerable reduction of the required spectrometer time. 13C R1, R2, 1H-->13C NOE were obtained, as well as the variations of R1 rho (90 degrees) as a function of the rf field strength. These data were compared to those recorded by 1H and 15N NMR on a labelled sample of the toxin [Guenneugues et al. (1997) Biochemistry, 36, 16097-16108]. Both sets of data showed that picosecond to nanosecond time scale motions are well correlated to the secondary structure of the protein. This was further reinforced by the analysis of a 1 ns molecular dynamics simulation in water. Several C alpha H alpha and threonine C beta H beta experimentally exhibit fast motions with a correlation time longer than 500 ps, that cannot be sampled along the simulation. In addition, the backbone exhibits motions on the microsecond to millisecond time scale on more than half of its length. Thus, toxin alpha, a highly stable protein (Tm = 75 degrees C at acidic pH) containing 61 amino acids and 4 disulfides, shows important internal motions on time scales ranging from 0.1-0.5 ps, to 10-100 ps, 1 ns, and about 30 microseconds to 10 ms. PMID:10382305

Guenneugues, M; Gilquin, B; Wolff, N; Ménez, A; Zinn-Justin, S

1999-05-01

256

Determination of organic milk authenticity using carbon and nitrogen natural isotopes.  

PubMed

Natural stable isotopes of carbon and nitrogen ((12)C, (13)C, (14)N, (15)N) have abundances unique to each living creature. Therefore, measurement of the stable isotope ratio of carbon and nitrogen (?(13)C=(13)C/(12)C, ?(15)N=(15)N/(14)N) in milk provides a reliable method to determine organic milk (OM) authenticity. In the present study, the mean ?(13)C value of OM was higher than that of conventional milk (CM), whereas the mean ?(15)N value of OM was lower than that of CM; nonetheless both ?(13)C and ?(15)N values were statistically different for the OM and CM (P<0.05). Furthermore, the values of ?(13)C and ?(15)N were found to differ statistically with the collection date and the milk brand (P<0.05). The combination of ?(13)C and ?(15)N values was more effective than either value alone in distinguishing between OM and CM. The results of the present study, which is based on preliminary data from a limited sample size and sampling period, could be highly valuable and helpful for consumers, the food industry, and/or government regulatory agencies as it can prevent fraudulent labelling of organic food. Further studies include additional analyses of other milk brands and analyses over longer time periods in order to accurately determine OM authenticity using stable isotopes of carbon and nitrogen. PMID:24799230

Chung, Ill-Min; Park, Inmyoung; Yoon, Jae-Yeon; Yang, Ye-Seul; Kim, Seung-Hyun

2014-10-01

257

First Experimental Measurement of the 18O(p,?)15N Reaction at Astrophysical Energies  

NASA Astrophysics Data System (ADS)

The 18O(p,?)15N and 17O(p,?)14N reactions are of primary importance in several as-trophysical scenarios, including nucleosynthesis inside Asymptotic Giant Branch stars and oxygen and nitrogen isotopic ratios in meteorite grains. They are also key reactions to understand exotic systems such as R-Coronae Borealis stars and novae. Thus, the measurement of their cross sections in the low energy region can be crucial to reduce the nuclear uncertainty on theoretical predictions, because the resonance parameters are poorly determined. The Trojan Horse Method, in its newly developed form particularly suited to investigate low-energy resonances, has been applied to the 2H(18O,?15N)n and 2H(17O,?14N)n reactions to deduce the 18O(p,?)15N and 17O(p,?)14N cross sections at low energies. Resonances in the 18O(p,?)15N and 17O(p,?)14N excitation functions have been studied and the resonance parameters deduced.

La Cognata, M.; Sergi, M. L.; Spitaleri, C.; Mukhamedzhanov, A.; Coc, A.; Cherubini, S.; Goldberg, V.; Gulino, M.; Hammache, F.; Irgaziev, B.; Kiss, G.; Lamia, L.; Pizzone, R. G.; Romano, S.; de Sereville, N.; Tribble, R.; Tumino, A.

2010-11-01

258

Fast hydrogen exchange affects 15N relaxation measurements in intrinsically disordered proteins  

PubMed Central

Unprotected amide protons can undergo fast hydrogen exchange (HX) with protons from the solvent. Generally, NMR experiments using the out-and-back coherence transfer with amide proton detection are affected by fast HX and result in reduced signal intensity. When one of these experiments, 1H-15N HSQC, is used to measure the 15N transverse relaxation rate (R2), the measured R2 rate is convoluted with the HX rate (kHX) and has higher apparent R2 values. Since the 15N R2 measurement is important for analyzing protein backbone dynamics, the HX effect on the R2 measurement is investigated and described here by multi-exponential signal decay. We demonstrate these effects by performing 15N R2CPMG experiments on ?-synuclein, an intrinsically disordered protein (IDP), in which the amide protons are exposed to solvent. We show that the HX effect on R2CPMG can be extracted by the derived equation. In conclusion, the HX effect may be pulse sequence specific and results from various sources including the J coupling evolution, the change of steady state water proton magnetization, and the D2O content in the sample. To avoid the HX effect on the analysis of relaxation data of unprotected amides, it is suggested that NMR experimental conditions insensitive to the HX should be considered or that intrinsic R2CPMG values be obtained by methods described herein.

Kim, Seho; Wu, Kuen-Phon; Baum, Jean

2013-01-01

259

Exploration of the nitrogen transport system of a nodulated legume using 15 N  

Microsoft Academic Search

Feeding experiments using 15N2 or 15NO3 are described investigating the transport of nitrogen in the field pea (Pisum arvense L.). Nitrogen assimilated by root or nodules moves preferentially upwards to the shoot through the xylem. Parts of the root below or distal to a region of assimilation can benefit from this nitrogen but do so to a much greater extent

C. G. O. Oghoghorie; J. S. Pate

1972-01-01

260

Tracing Nitrogen through Landscapes to Coastal Wetlands using d15N of Larval Fish  

EPA Science Inventory

Our objective was to evaluate the use of the nitrogen stable isotope value (d15N) of larval fish as an indicator of incipient anthropogenic nitrogen loading to coastal wetlands in the Great Lakes. We sampled coastal wetlands in five Lake Superior south shore tributaries that had ...

261

The use of delta(15)N in assessing sewage stress on coral reefs.  

PubMed

While coral reefs decline, scientists argue, and effective strategies to manage land-based pollution lag behind the extent of the problem. There is need for objective, cost-effective, assessment methods. The measurement of stable nitrogen isotope ratios, delta(15)N, in tissues of reef organisms shows promise as an indicator of sewage stress. The choice of target organism will depend upon study purpose, availability, and other considerations such as conservation. Algae are usually plentiful and have been shown faithfully to track sewage input. The organic matrix of bivalve shells can provide time series spanning, perhaps, decades. Gorgonians have been shown to track sewage, and can provide records potentially centuries-long. In areas where baseline data are lacking, which is almost everywhere, delta(15)N in gorgonians can provide information on status and trends. In coral tissue, delta(15)N combined with insoluble residue determination can provide information on both sewage and sediment stress in areas lacking baseline data. In the developed world, delta(15)N provides objective assessment in a field complicated by conflicting opinions. Sample handling and processing are simple and analysis costs are low. This is a method deserving widespread application. PMID:19286230

Risk, Michael J; Lapointe, Brian E; Sherwood, Owen A; Bedford, Bradley J

2009-06-01

262

? 15N values in Lake Erie sediments as indicators of nitrogen biogeochemical dynamics during cultural eutrophication  

Microsoft Academic Search

We have measured the stable nitrogen isotope values (?15N) in two sediment cores sampled 15years apart (1988 and 2003) from the Eastern Basin of Lake Erie and compared them to the total phosphorus (TP) and biogenic silica (BSi) concentrations in the 2003 core. Changes in the TP, BSi and total nitrogen (TN) accumulations in the 2003 core correspond to three

Yuehan Lu; Philip A. Meyers; Thomas H. Johengen; Brian J. Eadie; John A. Robbins; Haejin Han

2010-01-01

263

Using a Macroalgal d15N Bioassay to Detect Cruise Ship Waste Water Effluent Inputs  

EPA Science Inventory

Nitrogen stable isotopes are a powerful tool for tracking sources of N to marine ecosystems. I used green macroalgae as a bioassay organism to evaluate if the d15N signature of cruise ship waste water effluent (CSWWE) could be detected in Skagway Harbor, AK. Opportunistic green...

264

Assignment of paramagnetic (15)N-HSQC spectra by heteronuclear exchange spectroscopy.  

PubMed

Paramagnetic metal ions in proteins provide a rich source of structural information, but the resonance assignments required to extract the information can be challenging. Here we demonstrate that paramagnetically shifted (15)N-HSQC cross-peaks can be assigned using N(Z)-exchange spectroscopy under conditions in which the paramagnetic form of the protein is in dynamic equilibrium with its diamagnetic form. Even slow exchange of specifically bound metal ions may be detected within the long lifetime of (15)N longitudinal magnetization of large proteins at high magnetic fields. Alternatively, the exchange can be accelerated using an excess of metal ions. In the resulting exchange spectra, paramagnetic (15)N resonances become visible for residues that are not directly observed in a conventional (15)N-HSQC spectrum due to paramagnetic (1)H(N) broadening. The experiments are illustrated by the 30 kDa lanthanide-binding epsilon186/theta complex of DNA polymerase III in the presence of sub-stoichiometric amounts of Dy(3+) or a mixture of Dy(3+) and La(3+). PMID:17096205

John, Michael; Headlam, Madeleine J; Dixon, Nicholas E; Otting, Gottfried

2007-01-01

265

(1)H, (13)C, and (15)N resonance assignment of photoactive yellow protein.  

PubMed

Photoactive yellow protein (PYP) is involved in the negative phototactic response towards blue light of the bacterium Halorhodospira halophila. Here, we report nearly complete backbone and side chain (1)H, (13)C and (15)N resonance assignments at pH 5.8 and 20 °C of PYP in its electronic ground state. PMID:22528767

Pool, Trijntje J; Oktaviani, Nur Alia; Kamikubo, Hironari; Kataoka, Mikio; Mulder, Frans A A

2013-04-01

266

The effect of dietary nitrogen content on trophic level 15N enrichment  

Microsoft Academic Search

Given the great potential value of stable isotopes in a variety of scientific investigations, surprisingly little attention has been paid to the underlying physiological and biochemical mechanisms that account for trophic in- creases in d 15 N values. This has lead to a general call for controlled studies investigating the relationship between organismal diet and corresponding isotopic composition. We conducted

Thomas S. Adams; Robert W. Sterner

2000-01-01

267

Dinitrogen fixation estimates in vetch-barley swards using (sup 15) N methodology.  

National Technical Information Service (NTIS)

N(sub 2) fixation in vetch (Vicia Sativa) grown alone and in mixture with barley (Hordeum vulgare) in pots was evaluated using (sup 15) N isotope dilution method. Two harvests were made over the growing season. The proportion of the above-ground N derived...

F. Kurdali N. E. Sharabi

1992-01-01

268

Nitrogen cycling assessment in a hedgerow intercropping system using 15 N enrichment  

Microsoft Academic Search

Nitrogen (N) cycling was determined in monocultures of Sorghumbicolor (L.) Moench and alley cropped sorghum with Acaciasaligna (Labill.) H. Wendl. in semiarid Northern Kenya. N inputthrough biological N2 fixation of the acacia, N transfer from thelegume to the intercrop and losses of applied N through harvest and leachingwere estimated using 15N enrichment. The biological N2fixation and N transfer estimates clearly

Johannes Lehmann; Gerhard Gebauer; Wolfgang Zech

2002-01-01

269

The course of 15 N-ammonium nitrate in a spring barley cropping system  

Microsoft Academic Search

15N-labelled ammonium nitrate was applied to spring barley growing on a Cambisol soil in western Switzerland. Immobilization, plant uptake and disappearance of inorganic nitrogen were followed at frequent intervals. Fertilizer nitrogen disappeared shortly after its application, mainly through immobilization by soil microorganisms and absorption by the crop. Some of the added nitrogen was probably denitrified as a result of humid

G. J. M. Vos; B. Duquet; J. C. Vedy; J. A. Neyroud

1993-01-01

270

1H, 13C, and 15N resonance assignments of murine amelogenin, an enamel biomineralization protein  

PubMed Central

Amelogenin is the predominant matrix protein in developing dental enamel. Making extensive use of residue-specific 15N-labeled amino acids samples, the majority of the main and side chain resonances for murine amelogenin were assigned in 2% aqueous acetic acid at pH 3.0.

Buchko, Garry W.; Bekhazi, Jacky; Cort, John R.; Valentine, Nancy B.; Snead, Malcolm L.; Shaw, Wendy J.

2008-01-01

271

Preservation of Isotopic Signals ( 13 C, 15 N)_in Pleistocene Mammals  

Microsoft Academic Search

The preservation of biogenic isotopic signals (13C, 15N) in fossil bones and teeth is critical in order to interpret paleodiets. Some patterns of variation of these biogenic isotopic signals are characteristic of modern mammals, and their recognition in fossil samples provides a clue for the preservation of biogenic paleodietary signals.

Hervé Bocherens

272

Unusually negative nitrogen isotopic compositions (?15N) of mangroves and lichens in an oligotrophic, microbially-influenced ecosystem  

NASA Astrophysics Data System (ADS)

Extremes in ?15N values in mangrove tissues and lichens (range =+4 to -22‰) were measured from a mangrove forest ecosystem located on Twin Cays, offshore islands in Belize, Central America. The N isotopic compositions and concentrations of NH4+/NH3 in porewater, rainwater, and atmospheric ammonia, and the ?15N of lichens, mangrove leaves, roots, stems, and wood were examined to study the biogeochemical processes important for establishing these unusual N isotopic ratios. Dwarfed Rhizophora mangle trees had the most negative ?15N, whereas fringing Rhizophora trees, the most positive ?15N values. Porewater ammonium concentrations had little relationship to N isotopic fractionation in mangrove tissues. In dwarfed mangroves, the ?15N of fine and coarse roots were 6-9‰ more positive than leaf tissue from the same tree, indicating different sources of N for root and leaf tissues. When P was added to dwarfed mangrove trees without added N, ?15N increased within one year from -12‰ to -2‰, approaching the ?15N of porewater ammonium (?15N=+4‰). Isotopically depleted ammonia in the atmosphere (?15N=-19‰) and in rainwater (?15N=-10‰) were found on Twin Cays. We propose that foliar uptake of these atmospheric sources by P-stressed, dwarfed mangrove trees and lichens can explain their very negative ?15N values. In environments where P is limiting for growth, uptake of atmospheric N by Rhizophora mangle may be an important adaptive strategy.

Fogel, M. L.; Wooller, M. J.; Cheeseman, J.; Smallwood, B. J.; Roberts, Q.; Romero, I.; Meyers, M. J.

2008-12-01

273

The degree of urbanization across the globe is not reflected in the ?(15)N of seagrass leaves.  

PubMed

Many studies show that seagrass ?(15)N ratios increase with the amount of urbanization in coastal watersheds. However, there is little information on the relationship between urbanization and seagrass ?(15)N ratios on a global scale. We performed a meta-analysis on seagrass samples from 79 independent locations to test if seagrass ?(15)N ratios correlate with patterns of population density and fertilizer use within a radius of 10-200km around the sample locations. Our results show that seagrass ?(15)N ratios are more influenced by intergeneric and latitudinal differences than the degree of urbanization or the amount of fertilizer used in nearby watersheds. The positive correlation between seagrass ?(15)N ratios and latitude hints at an underlying pattern in discrimination or a latitudinal gradient in the (15)N isotopic signature of nitrogen assimilated by the plants. The actual mechanisms responsible for the correlation between ?(15)N and latitude remain unknown. PMID:23866922

Christiaen, Bart; Bernard, Rebecca J; Mortazavi, Behzad; Cebrian, Just; Ortmann, Alice C

2014-06-30

274

**1**5N-NMR INVESTIGATION OF HYDROXYLAMINE DERIVATIZED HUMIC SUBSTANCES.  

USGS Publications Warehouse

Humic substances are the most abundant naturally occurring refactory organic compounds in soils and water. They have a broad range of physical, chemical and physiological properties. In soils, humic substances contribute to the cation exchange capacity, help maintain the physical structure, and play a role in plant growth and nutrition. In aquatic systems, humic substances serve to regulate the levels of inorganic constituents, yield trihalomethanes upon chlorination, and transport or concentrate organic and inorganic pollutants. The oxygen containing functional groups of humic and fulvic acids are believed to play a key role in the chemical properties of humic substances. This study was undertaken to gain additional information on the specific types of oxygen functionalities in humic substances. Since the analysis of hydroxyl moieties had been earlier established, we focused our attention on the analysis of ketone and aldehyde functional groups in humic substances.

Thorn, Kevin, A.; Arterburn, Jeffrey, B.; Mikita, Michael, A.

1986-01-01

275

Determination of 15N chemical shift anisotropy from a membrane bound protein by NMR spectroscopy  

PubMed Central

Chemical shift anisotropy (CSA) tensors are essential in the structural and dynamic studies of proteins using NMR spectroscopy. Results from relaxation studies in biomolecular solution and solid-state NMR experiments on aligned samples are routinely interpreted using well-characterized CSA tensors determined from model compounds. Since CSA tensors, particularly the 15N CSA, highly depend on a number of parameters including secondary structure, electrostatic interaction and the amino acid sequence, there is a need for accurately determined CSA tensors from proteins. In this study we report the backbone amide-15N CSA tensors for a 16.7-kDa membrane-bound and paramagnetic-heme containing protein, rabbit cytochrome b5 (cytb5), determined using the 15N CSA/15N-1H dipolar transverse cross-correlation rates. The mean values of 15N CSA determined for residues in helical, sheet and turn regions are ?187.9, ?166.0, and ?161.1 ppm, respectively, with an overall average value of ?171.7 ppm. While the average CSA value determined from this study is in good agreement with previous solution NMR experiments on small globular proteins, the CSA value determined for residues in helical conformation is slightly larger which may be attributed to the paramagnetic effect from Fe(III) of the heme unit in cytb5. However, like in previous solution NMR studies, the CSA values reported in this study are larger than the values measured from solid-state NMR experiments. We believe that the CSA parameters reported in this study will be useful in determining the structure, dynamics and orientation of proteins, including membrane proteins, using NMR spectroscopy.

Pandey, Manoj Kumar; Vivekanandan, Subramanian; Ahuja, Shivani; Pichumani, Kumar; Im, Sang-Choul; Waskell, Lucy; Ramamoorthy, Ayyalusamy

2012-01-01

276

Gas Chromatography-Mass Spectrometry of N- Heptafluorobutyryl Isobutyl Esters of Amino Acids in the Analysis of the Kinetics of [15N]H4+ Assimilation in Lemna minor L  

PubMed Central

Rapid, sensitive, and selective methods for the determination of the 15N abundance of amino acids in isotopic tracer experiments with plant tissues are described and discussed. Methodology has been directly tested in an analysis of the kinetics of [15N]H4+ assimilation in Lemna minor L. The techniques utilize gas chromatography-mass spectrometry selected ion monitoring of major fragments containing the N moiety of N-heptafluorobutyryl isobutyl esters of amino acids. The ratio of selected ion pairs at the characteristic retention time of each amino acid derivative can be used to calculate 15N abundance with an accuracy of ±1 atom% excess 15N using samples containing as little as 30 picomoles of individual amino acids. Up to 11 individual amino acid derivatives can be selectively monitored in a single chromatogram of 30 minutes. It is suggested that these techniques will be useful in situations where the small quantities of N available for analysis have hitherto hindered the use of 15N-labeled precursors.

Rhodes, David; Myers, Ann C.; Jamieson, Gene

1981-01-01

277

Abiotic and biotic factors associated with the presence of Anopheles arabiensis immatures and their abundance in naturally occurring and manmade aquatic habitats.  

PubMed

ABSTRACT: BACKGROUND: Anopheles arabiensis (Diptera: Culicidae) is a potential malaria vector commonly present at low altitudes in remote areas in Reunion Island. Little attention has been paid to the environmental conditions driving larval development and abundance patterns in potential habitats. Two field surveys were designed to determine whether factors that discriminate between aquatic habitats with and without An. arabiensis larvae also drive larval abundance, comparatively in man-made and naturally occurring habitats. METHODS: In an initial preliminary survey, a representative sample of aquatic habitats that would be amenable to an intensive long-term study were selected and divided into positive and negative sites based on the presence or absence of Anopheles arabiensis larvae. Subsequently, a second survey was prompted to gain a better understanding of biotic and abiotic drivers of larval abundance, comparatively in man-made and naturally occurring habitats in the two studied locations. In both surveys, weekly sampling was performed to record mosquito species composition and larval density within individual habitats, as well as in situ biological characteristics and physico-chemical properties. RESULTS: Whilst virtually any stagnant water body could be a potential breeding ground for An. arabiensis, habitats occupied by their immatures had different structural and biological characteristics when compared to those where larvae were absent. Larval occurrence seemed to be influenced by flow velocity, macrofauna diversity and predation pressure. Interestingly, the relative abundance of larvae in man-made habitats (average: 0.55 larvae per dip, 95%CI [0.3-0.7]) was significantly lower than that recorded in naturally occurring ones (0.74, 95%CI [0.5-0.8]). Such differences may be accounted for in part by varying pressures that could be linked to a specific habitat. CONCLUSIONS: If the larval ecology of An. arabiensis is in general very complex and factors affecting breeding site productivity sometimes not easy to highlight, our results, however, highlight lower populations of An. arabiensis immatures compared to those reported in comparable studies conducted in the African continent. Overall, this low larval abundance, resulting from both abiotic and biotic factors, suggests that vector control measures targeting larval habitats are likely to be successful in Reunion, but these could be better implemented by taking environmental variability into account. PMID:22608179

Gouagna, Louis Clément; Rakotondranary, Manpionona; Boyer, Sebastien; Lempérière, Guy; Dehecq, Jean-Sébastien; Fontenille, Didier

2012-05-19

278

Abiotic and biotic factors associated with the presence of Anopheles arabiensis immatures and their abundance in naturally occurring and man-made aquatic habitats  

PubMed Central

Background Anopheles arabiensis (Diptera: Culicidae) is a potential malaria vector commonly present at low altitudes in remote areas in Reunion Island. Little attention has been paid to the environmental conditions driving larval development and abundance patterns in potential habitats. Two field surveys were designed to determine whether factors that discriminate between aquatic habitats with and without An. arabiensis larvae also drive larval abundance, comparatively in man-made and naturally occurring habitats. Methods In an initial preliminary survey, a representative sample of aquatic habitats that would be amenable to an intensive long-term study were selected and divided into positive and negative sites based on the presence or absence of Anopheles arabiensis larvae. Subsequently, a second survey was prompted to gain a better understanding of biotic and abiotic drivers of larval abundance, comparatively in man-made and naturally occurring habitats in the two studied locations. In both surveys, weekly sampling was performed to record mosquito species composition and larval density within individual habitats, as well as in situ biological characteristics and physico-chemical properties. Results Whilst virtually any stagnant water body could be a potential breeding ground for An. arabiensis, habitats occupied by their immatures had different structural and biological characteristics when compared to those where larvae were absent. Larval occurrence seemed to be influenced by flow velocity, macrofauna diversity and predation pressure. Interestingly, the relative abundance of larvae in man-made habitats (average: 0.55 larvae per dip, 95%CI [0.3–0.7]) was significantly lower than that recorded in naturally occurring ones (0.74, 95%CI [0.5–0.8]). Such differences may be accounted for in part by varying pressures that could be linked to a specific habitat. Conclusions If the larval ecology of An. arabiensis is in general very complex and factors affecting breeding site productivity sometimes not easy to highlight, our results, however, highlight lower populations of An. arabiensis immatures compared to those reported in comparable studies conducted in the African continent. Overall, this low larval abundance, resulting from both abiotic and biotic factors, suggests that vector control measures targeting larval habitats are likely to be successful in Reunion, but these could be better implemented by taking environmental variability into account.

2012-01-01

279

Abundances of a bean bug and its natural enemy in seminatural and cultivated habitats in agricultural landscapes.  

PubMed

To determine differences in distribution patterns between the soybean pest Riptortus pedestris F. (Hemiptera: Alydidae) and its egg parasitoid Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) in source and cultivated habitats, we compared their abundances in soybean fields and forest edges, which were assumed to be the overwintering sites of R. pedestris. We set synthetic attractant-baited traps for both species over 2 yr in mid-August, just before R. pedestris normally colonizes soybeans. During one of the 2 yr, we also examined the rate of parasitism using an egg trap. The numbers of both R. pedestris and O. nezarae trapped at forest edges were higher than the numbers caught in soybean fields, suggesting that forest edges are important source habitats. Compared with R. pedestris, the abundance of O. nezarae in soybean fields was considerably lower than in forest edges, presumably because of differences in their dispersal abilities and their responses to landscape structure and resource distribution. Better pest control service by O. nezarae was provided at forest edges than in soybean fields. Therefore, when using pest control by O. nezarae in soybean fields, spatial arrangement and distance from the forest edge should be considered. PMID:24534078

Tabuchi, Ken; Taki, Hisatomo; Iwai, Hideki; Mizutani, Nobuo; Nagasaka, Koukichi; Moriya, Seiichi; Sasaki, Rikiya

2014-04-01

280

Abundance and seasonal activity of questing Ixodes ricinus ticks in their natural habitats in southern Germany in 2011.  

PubMed

Questing ticks were sampled monthly over a period of 11 months from February, 2011 to December, 2011 at 13 sites in southern Germany using the flagging method. The ticks were identified to species, gender, and stadium. Although both I. ricinus and D. reticulatus were sampled, this study concentrated on I. ricinus, since it was the most abundant tick to be found. Additional weather data (air and soil temperature, relative air humidity, precipitation, sunshine duration) were recorded on each sampling site and the local vegetation described. A total of 14, 394 ticks was collected (7,862 larvae, 5,568 nymphs, 964 adults) and their activity was recorded in order to determine the seasonal activity pattern over different periods of the year. In contrast to the widely accepted pattern of a bimodal seasonal activity in moderate areas with a dominant peak in spring and a minor peak in autumn, a unimodal activity pattern was found for all development stages on six of the 12 sampling sites. Tick abundance was compared to weather variables. Tick host-seeking activity was found to be significantly dependent on the temperature at ground level, precipitation, and sunshine duration as well as relative air humidity. Adult ticks showed a positive correlation with the duration of sunshine, whereas nymphs were mostly unaffected by this phenomenon. PMID:24820556

Schulz, Michaela; Mahling, Monia; Pfister, Kurt

2014-06-01

281

The origin of nitrogen on Jupiter and Saturn from the 15N/14N ratio  

NASA Astrophysics Data System (ADS)

The Texas Echelon cross Echelle Spectrograph (TEXES), mounted on NASA’s Infrared Telescope Facility (IRTF), was used to map mid-infrared ammonia absorption features on both Jupiter and Saturn in February 2013. Ammonia is the principle reservoir of nitrogen on the giant planets, and the ratio of isotopologues (15N/14N) can reveal insights into the molecular carrier (e.g., as N2 or NH3) of nitrogen to the forming protoplanets, and hence the source reservoirs from which these worlds accreted. We targeted two spectral intervals (900 and 960 cm-1) that were relatively clear of terrestrial atmospheric contamination and contained close features of 14NH3 and 15NH3, allowing us to derive the ratio from a single spectrum without ambiguity due to radiometric calibration (the primary source of uncertainty in this study). We present the first ground-based determination of Jupiter’s 15N/14N ratio (in the range from 1.4×10-3 to 2.5×10-3), which is consistent with both previous space-based studies and with the primordial value of the protosolar nebula. On Saturn, we present the first upper limit on the 15N/14N ratio of no larger than 2.0×10-3 for the 900-cm-1 channel and a less stringent requirement that the ratio be no larger than 2.8×10-3 for the 960-cm-1 channel (1? confidence). Specifically, the data rule out strong 15N-enrichments such as those observed in Titan’s atmosphere and in cometary nitrogen compounds. To the extent possible with ground-based radiometric uncertainties, the saturnian and jovian 15N/14N ratios appear indistinguishable, implying that 15N-enriched ammonia ices could not have been a substantial contributor to the bulk nitrogen inventory of either planet. This result favours accretion of primordial N2 on both planets, either in the gas phase from the solar nebula, or as ices formed at very low temperatures. Finally, spatially-resolved TEXES observations are used to derive zonal contrasts in tropospheric temperatures, phosphine and 14NH3 on both planets, allowing us to relate thermal conditions and chemical compositions to phenomena observed at visible wavelengths in 2013 (e.g., Jupiter’s faint equatorial red colouration event and wave activity in the equatorial belts, plus the remnant warm band on Saturn following the 2010-11 springtime storm).

Fletcher, Leigh N.; Greathouse, T. K.; Orton, G. S.; Irwin, P. G. J.; Mousis, O.; Sinclair, J. A.; Giles, R. S.

2014-08-01

282

Heavy ? 15N in Intertidal Benthic Algae and Invertebrates in the Scheldt Estuary (The Netherlands): Effect of River Nitrogen Inputs  

NASA Astrophysics Data System (ADS)

The study investigated ? 15N in the intertidal benthic food webs from the middle Westerschelde Estuary and the middle Oosterschelde. Much heavier ? 15N values were observed for the main benthic primary producers and invertebrates in the Westerschelde Estuary. In the Oosterschelde, mean ? 15N values ranged from 1·4 to 7·3‰ for SOM and suspended POM, respectively, to 6·3 to 9·1‰ for Fucus vesiculosus and benthic diatoms, respectively. Mean ? 15N values in benthic invertebrates ranged from 9·7‰ for Gammarus locusta to 15·4‰ for Tubificoides sp. In the Westerschelde Estuary, mean ? 15N increased from 8·1 to 8·6‰ for suspended POM and SOM, respectively, to heavier ? 15N from 15·9 to 28·5‰ for F. vesiculosus and benthic diatoms, respectively. Mean ? 15N for intertidal invertebrates ranged from 18·1‰ for Lumbricillus sp. to 20·7‰ for Eulimnogammarus obtusatus. Higher enrichment in 15N in benthic primary producers and invertebrates from the Westerschelde Estuary are most likely due to the incorporation of 15N-enriched DIN carried by the Scheldt River by benthic algae and, then by benthic consumers. These results point to the fact that ? 15N in benthic estuarine food webs may respond directly to anthropogenic nitrogen inputs delivered into estuaries by rivers which drain highly urbanized areas.

Riera, P.; Stal, L. J.; Nieuwenhuize, J.

2000-09-01

283

Effects of forest decline on uptake and leaching of deposited nitrate determined from 15N and 18O measurements  

Microsoft Academic Search

ATTEMPTS to understand how atmospheric nitrogen deposition affects forest ecosystems1'2 have been hampered by the lack of a direct method to trace the fate of the deposited nitrogen. Nitrate originating in the atmosphere has natural abundances of nitrogen and oxygen isotopes that differ measurably from those of soil nitrate3. Here we present an analysis of the isotope ratios of nitrate

Walter Durka; Ernst-Detlef Schulze; Gerhard Gebauer; Susanne Voerkeliust

1994-01-01

284

Deuterium abundances  

NASA Astrophysics Data System (ADS)

We discuss the measurements of deuterium abundances in high redshift quasar absorbers, in the solar system and in the interstellar medium. We present new results that indicate spatial variations of the deuterium abundance in the interstellar medium at the level of ˜50% over scales possibly as small as ˜10 pc, and discuss plausible causes for the origin of these variations.

Lemoine, Martin; Audouze, Jean; Ben Jaffel, Lotfi; Feldman, Paul; Ferlet, Roger; Hébrard, Guillaume; Jenkins, Edward B.; Mallouris, Christoforos; Moos, Warren; Sembach, Kenneth; Sonneborn, George; Vidal-Madjar, Alfred; York, Donald G.

1999-07-01

285

2H(18F,p?)15N reaction applied to nova ?-ray emission  

NASA Astrophysics Data System (ADS)

The 18F(p,?)15O reaction is recognized to be one of the most important reactions for nova ?-ray astronomy, as it governs the early E<~511keV ? emission. However, in the nova temperature regime, its rate remains largely uncertain due to unknown low-energy resonance strengths. We report here the measurement of the 2H(18F,p)19F(?)15N one-nucleon transfer reaction, induced by a 14-MeV 18F radioactive beam impinging on a CD2 target; outgoing protons and 15N (or ? particles) were detected in coincidence in two silicon strip detectors. A distorted-wave Born approximation analysis of the data resulted in new limits to the contribution of low-energy resonances to the rate of the 18F(p,?)15O reaction.

de Séréville, N.; Coc, A.; Angulo, C.; Assunção, M.; Beaumel, D.; Bouzid, B.; Cherubini, S.; Couder, M.; Demaret, P.; de Oliveira Santos, F.; Figuera, P.; Fortier, S.; Gaelens, M.; Hammache, F.; Kiener, J.; Lefebvre, A.; Labar, D.; Leleux, P.; Loiselet, M.; Ninane, A.; Ouichaoui, S.; Ryckewaert, G.; Smirnova, N.; Tatischeff, V.; Thibaud, J.-P.

2003-05-01

286

Facile measurement of 1H-15N residual dipolar couplings in larger perdeuterated proteins  

PubMed Central

We present a simple method, ARTSY, for extracting 1JNH couplings and 1H-15N RDCs from an interleaved set of two-dimensional 1H-15N TROSY-HSQC spectra, based on the principle of quantitative J correlation. The primary advantage of the ARTSY method over other methods is the ability to measure couplings without scaling peak positions or altering the narrow line widths characteristic of TROSY spectra. Accuracy of the method is demonstrated for the model system GB3. Application to the catalytic core domain of HIV integrase, a 36 kDa homodimer with unfavorable spectral characteristics, demonstrates its practical utility. Precision of the RDC measurement is limited by the signal-to-noise ratio, S/N, achievable in the 2D TROSY-HSQC spectrum, and is approximately given by 30/(S/N) Hz.

Fitzkee, Nicholas C.; Bax, Ad

2010-01-01

287

Interference effects in proton scattering on {sup 15}N nuclei at intermediate energies  

SciTech Connect

The differential cross section for proton scattering on {sup 15}N nuclei is calculated within Glauber diffraction theory at energies of 0.2, 0.6, and 1.0 GeV. Use is made of the shell-model wave function for the {sup 15}N nucleus. The contribution of single and double collisions to the Glauber operator {Omega} is taken into account. The sensitivity of the differential cross sections to the contributions of scattering on nucleons from different shells, to the parameters of the elementary pN amplitude, and to the energy of projectile protons is investigated. It is shown that the interference between amplitudes corresponding to different collision multiplicities, as well as between the amplitudes for scattering on nucleons from different shells, determines special features of the cross section.

Ibraeva, E. T., E-mail: ibr@inp.k [National Nuclear Center of the Republic of Kazakhstan, Institute of Nuclear Physics (Kazakhstan); Zhusupov, M.A.; Imambekov, O. [Al-Farabi Kazakh National University (Kazakhstan); Krassovitskiy, P. M. [National Nuclear Center of the Republic of Kazakhstan, Institute of Nuclear Physics (Kazakhstan)

2010-08-15

288

1H, 13C and 15N resonance assignments of URNdesign, a computationally redesigned RRM protein  

SciTech Connect

Protein design represents one of the great challenges of computational structural biology. The ability to successfully design new proteins would allow us to generate new reagents and enzymes, while at the same time providing us with an understanding of the principles of protein stability. Here we report 1H, 15N and 13C resonance assignments of a redesigned U1A protein, URNdesign. U1A has been studied extensively by our group and hence was chosen as a design target. For the assignments we sued 2D and 3D heteronuclearNMR experiments with uniformly 13C, 15N-labeled URNdesign. The assignments for the backbone NH, CO,Ca and Cb nuclei are 94%complete. Sidechain 1Hand13C, aromatic andQ/NNH2 resonances are essentially complete with guanidinium and K NH3 residues unassigned. BMRB deposit with accession number 6493

Dobson, Neil; Dantas, Gautam; Varani, Gabriele

2005-10-01

289

A comparative study of platinum di(t-butyl)(15N2)diimine) and trans-[PtCl2(N-ligand)PBu3)] complexes by 195Pt, 31P- and 15N-NMR  

Microsoft Academic Search

195Pt-, 31P- and 15N-NMR. data are presented for [PtCl2 (t-Bu 15NCHCH15N (t-Bu)) (2-styrene)] (1), trans-[{PtCl2 (PBu3)}2 (t-Bu 15NCHCH15N (t-Bu))] (2), trans-[PtCl2 (t-Bu 15NCHCH15N (t-Bu)) (PBu3)] (3) and various complexes of the type trans-[PtCl2 (N-ligand) (PBu3)]. In solution the gross structural features of 1 and 2 are shown to be in agreement with those found in the solid state; namely, 1

G. van Koten; H. van der Poel; D. M. Grove; P. S. Pregosin; K. A. Ostoja Starzewski

1981-01-01

290

SEARCH FOR AN 80-ms SPONTANEOUS FISSION ACTIVITY IN BOMBARDMENTS OF 249Bk WITH 15N  

SciTech Connect

A rotating drum system was used to search for an 80-ms spontaneous fission (sf) activity in the reaction of {sup 15}N with {sup 249}Bk. No such activity was found beyond a cross section limit of 0.3 {+-} 0.3 nb. A sf activity with a half-life of about 20 ms and a formation cross section of 12 nb at 82 MeV was observed. The identity of this activity has not been determined.

Nitschke, J.M.; Fowler, M.; Ghiorso, A.; Leber, R.E.; Nurmia, M.J.; Somerville, L.P.; Williams, K.E.; Hulet, E.K.; Landrum, J.H.; Lougheed, R.W.; Wild, J.F.; Bemis, Jr., C.E.; Silva, R.J.; Eskola, P.

1980-01-01

291

15 N relaxation study of the cold shock protein CspB at various solvent viscosities  

Microsoft Academic Search

For a detailed NMR study of the dynamics of the cold shock protein CspB from Bacillus subtilis, we determined 15N transverse and longitudinal relaxation rates and heteronuclear nuclear Overhauser effects at different solvent viscosities.\\u000a Up to a relative viscosity of 2, which is equivalent to 27% ethylene glycol (EG), the overall correlation time follows the\\u000a linear Stokes-Einstein equation. At a

Markus Zeeb; Maik H. Jacob; Thomas Schindler; Jochen Balbach

2003-01-01

292

Nitrogen dynamics in paddy soil applied with various 15 N-labelled green manures  

Microsoft Academic Search

The effects of 15N-labelled green manure (GM) application on rice yield and N uptake were investigated and compared with those of inorganic\\u000a fertilizer (IF) and no fertilizer (NF) application. Nine GMs (white clover, Chinese milk vetch, hairy vetch, crimson clover,\\u000a oats, rye, Italian ryegrass, white mustard, lacy phacelia) were either incorporated into or surface-applied on paddy soil.\\u000a Among the nine

Naomi Asagi; Hideto Ueno

2009-01-01

293

Community 15N isoscapes to resolve plant-plant-interactions at the spatial scale  

NASA Astrophysics Data System (ADS)

Isoscapes have greatly improved our ability to understand biogeochemical processes on continental to global scales. However, the isoscapes framework may also have significant potential to resolve the spatial component of within-community interactions. For example, exotic plant invaders often exert strong impacts on ecosystem functioning, particularly regarding water-, carbon- and nutrient-cycles, but the spatial extent of such alterations is largely unknown. Here we show that massive N input by the N2-fixing exotic invasive Acacia longifolia to a Portuguese dune system can be traced using spatially resolved information on native plants' leaf ?15N. We found isotopic signatures of N to differ strongly between the native system (?15N c. -10 o) and the atmospherically derived N in A. longifolia phyllodes (?15N c. 0 o). Thus, sources of N for native plants could be readily distinguished. Leaf ?15N of a native, non-fixing species was increasingly enriched the closer the plant grew to the invader, indicating uptake of fixed N provided by A. longifolia. The enrichment was evident far beyond the stands of the invader, demonstrating that A. longifolia affected N budgets of native species up to a distance of 8 m exceeding the margin of the canopy. Furthermore, using the isoscapes approach, we were able to quantify the total area of N enrichment and could thus show that the area affected by invasion was at least 3.5 times larger than the area actually occupied by the invader. However, a native N2-fixing species had no such effects. Thus, downscaling isoscapes to the community level opens new frontiers in quantifying the spatial dimension of functional changes associated with plant invasions. Moreover, considering the feasibility and applicability of this approach, it may provide a promising tool to identify, quantify and monitor different types of functional plant-plant interactions within communities at a spatially explicit scale.

Hellmann, Christine; Rascher, Katherine G.; Máguas, Cristina; Werner, Christiane

2014-05-01

294

Manipulating the N release from 15N labelled celery residues by using straw and vinasses  

Microsoft Academic Search

The aim of this laboratory study was to investigate the effect of straw and vinasses on the nitrogen (N) mineralization–immobilization turnover of celery residues during two periods (each simulating a time period from autumn till spring) under laboratory conditions. During the first period (1–198d), 15N-labelled celery residues (1.1g dry matter (DM) kg?1 soil) were incubated together with straw (8.1g DMkg?1

B. Chaves; S. De Neve; P. Boeckx; C. Berko; O. Van Cleemput; G. Hofman

2006-01-01

295

Imperfect elasticity of steel Kh15N27T3MR  

Microsoft Academic Search

1.To obtain the minimal values of the characteristics of imperfect elasticity of precipitation-hardening spring steel Kh15N27T3MR we recommend quenching from 1050° and tempering at 750° for 5 h for the steel not strain hardened and at 700° for 5 h, 700° for 2 h, and 700° for 1 h for the steel deformed 17, 30, and 60%, respectively.2.Plastic deformation of

K. K. Balatskii; S. O. Tsobkallo; A. L. Selyavo; Z. M. Rulina; A. S. Moskalev

1977-01-01

296

Organic Matter Stable Isotope (? 13 C, ? 15 N) Response to Historical Eutrophication of Lake Taihu, China  

Microsoft Academic Search

We explored the use of carbon and nitrogen isotope ratios (?13C, ?15N) in sediment organic matter as proxy indicators of historical changes in the trophic state of Lake Taihu, the third largest\\u000a freshwater lake in China. Stable isotope signatures in four sediment cores spanning the 20th century were compared with instrumental\\u000a records of lake-water trophic state. The comparative study shows

Jinglu Wu; Lin Lin; Michael K. Gagan; Gerhard H. Schleser; Sumin Wang

2006-01-01

297

Potential of ? 13 C and ? 15 N of cladoceran subfossil exoskeletons for paleo-ecological studies  

Microsoft Academic Search

Stable isotope analyses on cladoceran subfossil exoskeletons retrieved from sediment cores could allow the reconstruction\\u000a of past changes in lake food webs provided the ?13C and ?15N values of the exoskeletons reflect those of the organisms’ whole body. The relationships between the C and N stable isotope\\u000a compositions of the exoskeletons and those of the whole body were investigated for

Marie-Elodie Perga

2010-01-01

298

The fate of labelled 15 N urea and ammonium nitrate applied to a winter wheat crop  

Microsoft Academic Search

A field experiment was conducted on a winter wheat crop in Northern France with either15N-urea or ammonium nitrate, labelled either on NH4 or on NO3. The fertilizer was split between two dressings, one applied in early March and the second in mid-April, labelled separately. N uptake by the crop was measured at 8 successive times after each dressing. The N

S. Recous; J. M. Machet; B. Mary

1988-01-01

299

DETERMINATION OF SENSITIVITY COEFFICIENTS FOR ROCKWELL HARDNESS SCALES HR15N, HR30N, AND HRA  

Microsoft Academic Search

This report describes the work carried out to provide sensitivity coefficients for the Rockwell HRA and Superficial Rockwell HR15N and HR30N scales. Sensitivity coefficients were determined for the preliminary test force, total test force, force duration times, loading times, and loading rates. 2. EQUIPMENT The NPL test work was performed in a 1.5 kN hardness standard machine (Fig. 1). Which

Laurence Brice; Samuel Low; Rodney Jiggetts

300

Seasonal uptake of 15 N-nitrate and distribution of absorbed nitrogen in peach trees  

Microsoft Academic Search

The absorption and distribution of N was measured monthly throught a calendar year in 3-year old peach trees (Prunus persica (L) c.v. Maycrest) grafted on Nemaguard rootstock. Plants were grown on siliceous sand in 500-L pots and fertilized with a solution containing 15N enriched KNO3. During flowering and fruit set (March) approximately 7% of N found in new growth came

N. Muñoz; J. Guerri; F. Legaz; E. Primo-millo

1993-01-01

301

A Survey of \\delta18O and \\delta15N Ratios in Ground Water from an Agricultural Community in the San Joaquin Valley, California  

NASA Astrophysics Data System (ADS)

We studied ground water samples from domestic and monitoring wells in an agricultural community in the eastern side of the San Joaquin Valley, California. The study area is rich in alluvial soils creating an extremely fertile farmland. Livestock farms and agricultural fields are abundant in the area. Fifty-four ground water samples were analyzed for \\delta18O and \\delta15N in dissolved nitrate, in addition to nutrients and major minerals. Nitrate concentration levels in groundwater are elevated and affected by agricultural and other activities. Possible sources of nutrients include: a municipal waste-water treatment facility, a raisin processing plant, a meat processing plant, a turkey farm, diary operations, and agricultural fields. However, except for the turkey farm and a diary, we found no statistical significant contribution of nitrate from the other facilities as compared to the rest of the area. The \\delta18O versus \\delta15N ratios plot of dissolved ground water nitrate shows most samples clustered around an area consistent with soil organic nitrogen. In addition, the rest of the samples show a trend that is indicative of denitrification process. Generally, high \\delta15N values are associated with low nitrate concentrations. The isotopic signal of denitrification is particularly pronounced in samples in the vicinity of the waste water treatment facility, where the highest values of \\delta15N and the lowest nitrate concentrations are observed. However, these samples also have elevated chloride concentrations indicating a waste-water source. These data suggest that the denitrification in the subsurface may have been enhanced by bacteria species introduced by the effluence of the plant. [This study was performed with the collaboration of Steven R Silva of USGS, Menlo Park, and Iris Yamagata and Holly Jo Ferrin of California Department of Water Resources.

Glowacki, S. D.; Suen, C. J.

2004-12-01

302

15N relaxation study of the cold shock protein CspB at various solvent viscosities.  

PubMed

For a detailed NMR study of the dynamics of the cold shock protein CspB from Bacillus subtilis, we determined (15)N transverse and longitudinal relaxation rates and heteronuclear nuclear Overhauser effects at different solvent viscosities. Up to a relative viscosity of 2, which is equivalent to 27% ethylene glycol (EG), the overall correlation time follows the linear Stokes-Einstein equation. At a relative viscosity of 6 (70% EG) the correlation time deviates from linearity by 30%, indicating that CspB tumbles at a higher rate as expected from the solvent viscosity probably due to a preferential binding of water molecules at the protein surface. The corresponding hydrodynamic radii, determined by NMR diffusion experiments, show no variation with viscosity. The amplitudes of intramolecular motions on a sub-nanosecond time scale revealed by an extended Lipari-Szabo analysis were mainly independent of the solvent viscosity. The lower limit of the NMR 'observation window' for the internal correlation time shifts above 0.5 ns at 70% EG, which is directly reflected in the experimentally derived internal correlation times. Chemical exchange contributions to the transverse relaxation rates derived from the Lipari-Szabo approach coincide with the experimentally determined values from the transverse (1)H-(15)N dipolar/(15)N chemical shift anisotropy relaxation interference. These contributions originate from fast protein folding reactions on a millisecond timescale, which get retarded at increased solvent viscosities. PMID:12975582

Zeeb, Markus; Jacob, Maik H; Schindler, Thomas; Balbach, Jochen

2003-11-01

303

Individual protein balance strongly influences ?15N and ?13C values in Nile tilapia, Oreochromis niloticus  

NASA Astrophysics Data System (ADS)

Although stable isotope ratios in animals have often been used as indicators of the trophic level and for the back-calculation of diets, few experiments have been done under standardized laboratory conditions to investigate factors influencing ?15N and ?13C values. An experiment using Nile tilapia [Oreochromis niloticus (L.)] was therefore carried out to test the effect of different dietary protein contents (35.4, 42.3, and 50.9%) on ?15N and ?13C values of the whole tilapia. The fish were fed the isoenergetic and isolipidic semi-synthetic diets at a relatively low level. ?15N and ?13C values of the lipid-free body did not differ between the fish fed the diets with different protein contents, but the trophic shift for N and C isotopes decreased with increasing protein accretion in the individual fish, for N from 6.5‰ to 4‰ and for C in the lipid-free body from 4‰ to 2.5‰. This is the first study showing the strong influence of the individual protein balance to the degree to which the isotopic signature of dietary protein was modified in tissue protein of fish. The extrapolation of the trophic level or the reconstruction of the diet of an animal from stable isotope ratios without knowledge of the individual physiological condition and the feeding rate may lead to erroneous results.

Gaye-Siessegger, Julia; Focken, Ulfert; Abel, Hansjörg; Becker, Klaus

304

Solid-state /sup 15/N NMR of oriented lipid bilayer bound gramicidin A'  

SciTech Connect

Highly oriented samples of lipid and gramicidin A' (8:1 molar ratio) have been prepared with the samples extensively hydrated (approximately 70% water v/w). These preparations have been shown to be completely in a bilayer phase with a transition temperature of 28/sup 0/C, and evidence is presented indicating that the gramicidin is in the channel conformation. An estimate of the disorder in the alignment of the bilayers parallel with the glass plates used to align the bilayers can be made from the asymmetry of the nuclear magnetic resonances (NMR). Such an analysis indicates a maximal range of disorder of +-3/sup 0/. Uniformly /sup 15/N-labeled gramicidin has been biosynthesized by Bacillus brevis grown in a media containing /sup 15/N-labeled Escherichia coli cells as the only nitrogen source. When prepared with labeled gramicidin, the oriented samples result in high-resolution /sup 15/N NMR spectra showing 12 resonances for the 20 nitrogen sites of the polypeptide. The frequency of the three major multiple resonance peaks has been interpreted to yield the approximate orientation of the N-H bonds in the peptide linkages with respect to the magnetic field. The bond orientations are only partially consistent with the extant structural models of gramicidin.

Nicholson, L.K.; Moll, F.; Mixon, T.E.; LoGrasso, P.V.; Lay, J.C.; Cross, T.A.

1987-10-20

305

Heathland vegetation as a bio-monitor for nitrogen deposition and source attribution using ?15N values  

NASA Astrophysics Data System (ADS)

The %N and ?15N signals in foliar nitrogen (N) from four heathland species have been monitored in a blanket bog plant community subjected to different experimental inputs of wet and dry N deposition. Interactions with combined additional treatments of phosphorus (P) and potassium (K) were also investigated. Calluna vulgaris, Cladonia portentosa, Sphagnum capillifolium and Hypnum cupressiforme were harvested for 15N analysis prior to wet and dry treatment applications and again after 16 months field exposure. A significant increase was observed in both %N and ?15N values for all plant species in response to both wet and dry treatments whilst PK additions also produced significant decreases in foliar %N and associated ?15N values for several of the species sampled. These enrichments in the ?15N signals for post-treatment shoot tissue were attributable to the ?15N signal in the source application, a finding of potential value in using bio-monitors for assessment of N deposition.

Skinner, R. A.; Ineson, P.; Jones, H.; Sleep, D.; Leith, I. D.; Sheppard, L. J.

306

Solution 1H, 15N NMR spectroscopic characterization of substrate-bound, cyanide-inhibited human heme oxygenase: water occupation of the distal cavity.  

PubMed

A solution NMR spectroscopic study of the cyanide-inhibited, substrate-bound complex of uniformly (15)N-labeled human heme oxygenase, hHO, has led to characterization of the active site with respect to the nature and identity of strong hydrogen bonds and the occupation of ordered water molecules within both the hydrogen bonding network and an aromatic cluster on the distal side. [(1)H-(15)N]-HSQC spectra confirm the functionalities of several key donors in particularly robust H-bonds, and [(1)H-(15)N]HSQC-NOESY spectra lead to the identification of three additional robust H-bonds, as well as the detection of two more relatively strong H-bonds whose identities could not be established. The 3D NMR experiments provided only a modest, but important, extension of assignments because of the loss of key TOCSY cross-peaks due to the line broadening from a dynamic heterogeneity in the active site. Steady-state NOEs upon saturating the water signal locate nine ordered water molecules in the immediate vicinity of the H-bond donors, six of which are readily identified in the crystal structure. The additional three are positioned in available spaces to account for the observed NOEs. (15)N-filtered steady-state NOEs upon saturating the water resonances and (15)N-filtered NOESY spectra demonstrate significant negative NOEs between water molecules and the protons of five aromatic rings. Many of the NOEs can be rationalized by water molecules located in the crystal structure, but strong water NOEs, particularly to the rings of Phe47 and Trp96, demand the presence of at least an additional two immobilized water molecules near these rings. The H-bond network appears to function to order water molecules to provide stabilization for the hydroperoxy intermediate and to serve as a conduit to the active site for the nine protons required per HO turnover. PMID:14583035

Li, Yiming; Syvitski, Ray T; Auclair, Karine; Ortiz de Montellano, Paul; La Mar, Gerd N

2003-11-01

307

Sensitivity enhancement in natural-abundance solid-state 33S MAS NMR spectroscopy employing adiabatic inversion pulses to the satellite transitions.  

PubMed

The WURST (wideband uniform rate smooth truncation) and hyperbolic secant (HS) pulse elements have each been employed as pairs of inversion pulses to induce population transfer (PT) between the four energy levels in natural abundance solid-state (33)S (spin I=3/2) MAS NMR, thereby leading to a significant gain in intensity for the central transition (CT). The pair of inversion pulses are applied to the satellite transitions for a series of inorganic sulfates, the sulfate ions in the two cementitious materials ettringite and thaumasite, and the two tetrathiometallates (NH(4))(2)WS(4) and (NH(4))(2)MoS(4). These materials all exhibit (33)S quadrupole coupling constants (C(Q)) in the range 0.1-1.0 MHz, with precise C(Q) values being determined from analysis of the PT enhanced (33)S MAS NMR spectra. The enhancement factors for the WURST and HS elements are quite similar and are all in the range 1.74-2.25 for the studied samples, in excellent agreement with earlier reports on HS enhancement factors (1.6-2.4) observed for other spin I=3/2 nuclei with similar C(Q) values (0.3-1.2 MHz). Thus, a time saving in instrument time by a factor up to five has been achieved in natural abundance (33)S MAS NMR, a time saving which is extremely welcome for this important low-gamma nucleus. PMID:18082436

Hansen, Michael Ryan; Brorson, Michael; Bildsøe, Henrik; Skibsted, Jørgen; Jakobsen, Hans J

2008-02-01

308

Sensitivity enhancement in natural-abundance solid-state 33S MAS NMR spectroscopy employing adiabatic inversion pulses to the satellite transitions  

NASA Astrophysics Data System (ADS)

The WURST (wideband uniform rate smooth truncation) and hyperbolic secant (HS) pulse elements have each been employed as pairs of inversion pulses to induce population transfer (PT) between the four energy levels in natural abundance solid-state 33S (spin I = 3/2) MAS NMR, thereby leading to a significant gain in intensity for the central transition (CT). The pair of inversion pulses are applied to the satellite transitions for a series of inorganic sulfates, the sulfate ions in the two cementitious materials ettringite and thaumasite, and the two tetrathiometallates (NH 4) 2WS 4 and (NH 4) 2MoS 4. These materials all exhibit 33S quadrupole coupling constants ( CQ) in the range 0.1-1.0 MHz, with precise CQ values being determined from analysis of the PT enhanced 33S MAS NMR spectra. The enhancement factors for the WURST and HS elements are quite similar and are all in the range 1.74-2.25 for the studied samples, in excellent agreement with earlier reports on HS enhancement factors (1.6-2.4) observed for other spin I = 3/2 nuclei with similar CQ values (0.3-1.2 MHz). Thus, a time saving in instrument time by a factor up to five has been achieved in natural abundance 33S MAS NMR, a time saving which is extremely welcome for this important low-? nucleus.

Hansen, Michael Ryan; Brorson, Michael; Bildsøe, Henrik; Skibsted, Jørgen; Jakobsen, Hans J.

2008-02-01

309

Foliar retention of 15N-nitrate and 15N-ammonium by red maple (Acer rubrum) and white oak (Quercus alba) leaves from simulated rain  

SciTech Connect

Studies of nitrogen cycling in forests indicate that trees assimilate atmospheric nitrate and ammonium and that differences between atmospheric deposition to the forest canopy and deposition measured in forest throughfall can be attributed to the removal of these ions from rain by tree leaves. Red maple and white oak leaves were exposed to artificial rain solutions (pH 4.1) containing {sup 15}N-labeled nitrate (3.5 {micro}g N/ml) or ammonium (2.2 {micro}g N/ml). At two time intervals after exposure (2 hr and 2 days) an exposed leaf and a control (non-exposed) leaf were removed from replicate seedlings. Based on results from {sup 15}N analysis, most of the nitrate applied to tree leaves was removed by washing with water; the mean per cent removal ({+-} standard error, N = 4) was 87 {+-} 1 and 73 {+-} 4% of the {sup 15}NO-N Applied to red maple and white oak leaves, respectively. Relative retention of {sup 15}NH{sub 4}-N by the leaves was greater than that observed for {sup 15}NO{sub 3}-N. In red maple and white oak leaves, 58 {+-} 9 and 84 {+-} 7% (mean {+-} standard error, N = 4), respectively, of the applied ammonium was not removed by washing treatments. Our results show that the foliar uptake of {sup 15}NH{sub 4}{sup +} from simulated rain by deciduous tree leaves is greater than that for {sup 15}NO{sub 3}{sup -}. Greater retention of NH{sub 4}{sup +} than NO{sub 3}{sup -} ions by red maple and white oak leaves from simulated rainfall is consistent with field observations showing a preferential retention of ammonium from rainfall by forest canopies. As nitrogen chemistry and the relative importance of nitrogen compounds in the atmosphere change in response to proposed emission reductions (and possibly climate change), an improved understanding of the fate of airborne nitrogen compounds in forest biogeochemical cycles will be necessary.

Garten Jr, Charles T [ORNL; Hanson, Paul J [ORNL

1990-07-01

310

Controls on Hyporheic Nitrate Removal: Assessing Transport and Substrate Limitations with 15N Tracer Studies (Invited)  

NASA Astrophysics Data System (ADS)

We examined transport time and substrate controls on hyporheic (HZ) nitrification and denitrification in an upland agricultural stream with a series of 15N tracer studies - whole-stream and in situ well-to-well steady-state 15NO3- and conservative tracer (Cl-) addition experiments. For the whole-stream experiment, we measured relevant solute, 15N isotope, and hydraulic transport conditions of the reach and along HZ flowpaths of an instrumented gravel bar. HZ exchange was observed across the entire gravel bar with flowpath lengths up to 4.2m and corresponding median residence times greater than 28.5h. The HZ transitioned from a net nitrification environment at its head (small residence times, <6.9h) to a net denitrification environment at its tail (large residence times, 6.9-28.5h). HZ denitrification was confirmed as 15N2 was produced across the entire gravel bar. Production of 15N2 across all observed flowpaths and residence times indicated that denitrification microsites are present even where net nitrification occurred. At large residence times, the rate of denitrification decreased despite persistent anoxic conditions, indicating substrate (NO3- and carbon) limitations. Consequently, we conducted in situ 15NO3-, conservative tracers (Cl- and Br), and acetate injection experiments to determine how the availability of labile dissolved organic carbon (DOC) as acetate influences microbial denitrification in the HZ, especially along anoxic flowpaths with large residence times. The acetate addition to the HZ stimulated significant increases in 15N2 production by factors of 2.7 to 26.1 in all receiving wells, and significant decreases of NO3- and DOC aromaticity in the wells most hydrologically connected to the injection. Further, 100% of acetate was retained in the HZ, a portion of which is due to biological consumption. These studies demonstrate that: 1. the HZ is an active nitrogen sink in this study system, 2. the distinction between net nitrification and denitrification in the HZ is a function of residence time and exhibits threshold behavior, and 3. microbial denitrification in anaerobic portions of the HZ can be limited by labile DOC supply.

Zarnetske, J. P.; Haggerty, R.; Wondzell, S. M.; Baker, M. A.

2010-12-01

311

Foliar ?15N is affected by foliar nitrogen uptake, soil nitrogen, and mycorrhizae along a nitrogen deposition gradient.  

PubMed

Foliar nitrogen isotope (?(15)N) composition patterns have been linked to soil N, mycorrhizal fractionation, and within-plant fractionations. However, few studies have examined the potential importance of the direct foliar uptake of gaseous reactive N on foliar ?(15)N. Using an experimental set-up in which the rate of mycorrhizal infection was reduced using a fungicide, we examined the influence of mycorrhizae on foliar ?(15)N in potted red maple (Acer rubrum) seedlings along a regional N deposition gradient in New York State. Mycorrhizal associations altered foliar ?(15)N values in red maple seedlings from 0.06 to 0.74 ‰ across sites. At the same sites, we explored the predictive roles of direct foliar N uptake, soil ?(15)N, and mycorrhizae on foliar ?(15)N in adult stands of A. rubrum, American beech (Fagus grandifolia), black birch (Betula lenta), and red oak (Quercus rubra). Multiple regression analysis indicated that ambient atmospheric nitrogen dioxide (NO2) concentration explained 0, 69, 23, and 45 % of the variation in foliar ?(15)N in American beech, red maple, red oak, and black birch, respectively, after accounting for the influence of soil ?(15)N. There was no correlation between foliar ?(13)C and foliar %N with increasing atmospheric NO2 concentration in most species. Our findings suggest that total canopy uptake, and likely direct foliar N uptake, of pollution-derived atmospheric N deposition may significantly impact foliar ?(15)N in several dominant species occurring in temperate forest ecosystems. PMID:23070141

Vallano, Dena M; Sparks, Jed P

2013-05-01

312

Variation in environmental conditions, understorey species number, abundance and composition among natural and managed Picea abies forest stands  

Microsoft Academic Search

We studied four south-facing and three north-facing boreal spruce forest stands (ca. 0.1ha each) in SE Norway with the aim of testing the hypothesis that former logging has long-term effects on boreal forest-floor vegetation. The stand series comprised unlogged natural forests and forests that were selectively or clear cut 60–70 years prior to our study. Each stand was described with

Tonje Økland; Knut Rydgren; Rune Halvorsen Økland; Ken Olaf Storaunet; Jørund Rolstad

2003-01-01

313

Determination of Natural 14C Abundances in Dissolved Organic Carbon in Organic-Rich Marine Sediment Porewaters by Thermal Sulfate Reduction  

NASA Astrophysics Data System (ADS)

The abundances of natural 14C in dissolved organic carbon (DOC) in the marine environment hold clues regarding the processes that influence the biogeochemical cycling of this large carbon reservoir. At present, UV irradiation is the widely accepted method for oxidizing seawater DOC for determination of their 14C abundances. This technique yields precise and accurate values with low blanks, but it requires a dedicated vacuum line, and hence can be difficult to implement. As an alternative technique that can be conducted on a standard preparatory vacuum line, we modified and tested a thermal sulfate reduction method that was previously developed to determine ?13C values of marine DOC (Fry B. et al., 1996. Analysis of marine DOC using a dry combustion method. Mar. Chem., 54: 191-201.) to determine the 14C abundances of DOC in marine sediment porewaters. In this method, the sample is dried in a 100 ml round-bottom Pyrex flask in the presence of excess oxidant (K2SO4) and acid (H3PO4), and combusted at 550 deg.C. The combustion products are cryogenically processed to collect and quantify CO2 using standard procedures. Materials we have oxidized to date range from 6-24 ml in volume, and 95-1500 ?gC in size. The oxidation efficiency of this method was tested by processing known amounts of reagent-grade dextrose and sucrose (as examples of labile organic matter), tannic acid and humic acid (as examples of complex natural organic matter), and porewater DOC extracted from organic-rich nearshore sediments. The carbon yields for all of these materials averaged 99±4% (n=18). The 14C abundances of standard materials IAEA C-6 and IAEA C-5 processed by this method using >1mgC aliquots were within error of certified values. The size and the isotopic value of the blank were determined by a standard dilution technique using IAEA C-6 and IAEA C-5 that ranged in size from 150 to 1500 ?gC (n=4 and 2, respectively). This yielded a blank size of 6.7±0.7 ?gC, and a blank isotopic value of 0.54±0.05 fMC. The size of the blank agreed well with that determined directly by processing variable volumes of UV-irradiated deionized water (5.6±0.7 ?gC, n=9). The size of the blank amounts to <~5% of the size of porewater DOC samples that are typically recovered from organic-rich sediment cores (~100-500 ?gC). The fMC value of the blank suggests that there may be multiple sources of extraneous carbon that range in 14C abundance. In order to assess the fidelity of 14C abundances in natural porewater DOC oxidized by thermal sulfate reduction, we oxidized porewater DOC samples collected from the central floor of the Santa Monica Basin, California Borderland, using both this method and UV irradiation (the latter carried out at the Druffel laboratory, University of California Irvine). The fMC values obtained by the two methods agreed within error. Carbon yields from the two methods also agreed closely. These findings show that thermal sulfate reduction may be a promising method to oxidize small, concentrated marine DOC samples for 14C analysis.

Johnson, L.; Komada, T.

2010-12-01

314

Indirect nuclear 15N-15N scalar coupling through a hydrogen bond: dependence on structural parameters studied by quantum chemistry tools.  

PubMed

NMR spin-spin couplings through a hydrogen bond in the free-base and protonated forms of the complete series of [(15)N2]-N-methylated 1,8-diaminonaphthalenes have been analyzed using quantum chemistry tools. The dominating role of the overlap of the coupling pathway orbitals has been demonstrated. The correlation of the sum of the (13)C NMR shifts of the naphthalene ring C(1,8) carbons directly attached to the interacting nitrogens with the J(N-N) values and the degree of methylation found earlier by G. C. Lloyd-Jones et al. [Chem.-Eur. J. 2003, 9, 4523] have been reexamined. It has been found that the correlations of J(N-N) and [??C(1,8)] with the degree of methylation have different reasons. While the former is mostly connected with the structural changes due to the solvent effect, the latter is attributed to the changes in the paramagnetic contributions from the C-N and C-C bonds caused by the replacement of a hydrogen by a methyl group. PMID:23987730

K?ístková, Anežka; Asher, James R; Malkin, Vladimir G; Malkina, Olga L

2013-09-26

315

A long N-terminal-extended nested set of abundant and antigenic major histocompatibility complex class I natural ligands from HIV envelope protein.  

PubMed

Viral antigens complexed with major histocompatibility complex (MHC) class I molecules are recognized by cytotoxic T lymphocytes on infected cells. Assays with synthetic peptides identify optimal MHC class I ligands often used for vaccines. However, when natural peptides are analyzed, more complex mixtures including long peptides bulging in the middle of the binding site or with carboxyl extensions are found, reflecting lack of exposure to carboxypeptidases in the antigen processing pathway. In contrast, precursor peptides are exposed to extensive cytosolic aminopeptidase activity, and fewer than 1% survive, only to be further trimmed in the endoplasmic reticulum. We show here a striking example of a nested set of at least three highly antigenic and similarly abundant natural MHC class I ligands, 15, 10, and 9 amino acids in length, derived from a single human immunodeficiency virus gp160 epitope. Antigen processing, thus, gives rise to a rich pool of possible ligands from which MHC class I molecules can choose. The natural peptide set includes a 15-residue-long peptide with unprecedented 6 N-terminal residues that most likely extend out of the MHC class I binding groove. This 15-mer is the longest natural peptide known recognized by cytotoxic T lymphocytes and is surprisingly protected from aminopeptidase trimming in living cells. PMID:16407287

Samino, Yolanda; López, Daniel; Guil, Sara; Saveanu, Loredana; van Endert, Peter M; Del Val, Margarita

2006-03-10

316

Supportive breeding boosts natural population abundance with minimal negative impacts on fitness of a wild population of Chinook salmon.  

PubMed

While supportive breeding programmes strive to minimize negative genetic impacts to populations, case studies have found evidence for reduced fitness of artificially produced individuals when they reproduce in the wild. Pedigrees of two complete generations were tracked with molecular markers to investigate differences in reproductive success (RS) of wild and hatchery-reared Chinook salmon spawning in the natural environment to address questions regarding the demographic and genetic impacts of supplementation to a natural population. Results show a demographic boost to the population from supplementation. On average, fish taken into the hatchery produced 4.7 times more adult offspring, and 1.3 times more adult grand-offspring than naturally reproducing fish. Of the wild and hatchery fish that successfully reproduced, we found no significant differences in RS between any comparisons, but hatchery-reared males typically had lower RS values than wild males. Mean relative reproductive success (RRS) for hatchery F(1) females and males was 1.11 (P = 0.84) and 0.89 (P = 0.56), respectively. RRS of hatchery-reared fish (H) that mated in the wild with either hatchery or wild-origin (W) fish was generally equivalent to W × W matings. Mean RRS of H × W and H × H matings was 1.07 (P = 0.92) and 0.94 (P = 0.95), respectively. We conclude that fish chosen for hatchery rearing did not have a detectable negative impact on the fitness of wild fish by mating with them for a single generation. Results suggest that supplementation following similar management practices (e.g. 100% local, wild-origin brood stock) can successfully boost population size with minimal impacts on the fitness of salmon in the wild. PMID:23025818

Hess, Maureen A; Rabe, Craig D; Vogel, Jason L; Stephenson, Jeff J; Nelson, Doug D; Narum, Shawn R

2012-11-01

317

Denitrification in nitrate-rich streams: application of N2:Ar and 15N-tracer methods in intact cores.  

PubMed

Rates of benthic denitrification were measured using two techniques, membrane inlet mass spectrometry (MIMS) and isotope ratio mass spectrometry (IRMS), applied to sediment cores from two NO3(-)-rich streams draining agricultural land in the upper Mississippi River Basin. Denitrification was estimated simultaneously from measurements of N2:Ar (MIMS) and 15N[N2] (IRMS) after the addition of low-level 15NO3- tracer (15N:N = 0.03-0.08) in stream water overlying intact sediment cores. Denitrification rates ranged from about 0 to 4400 micromol N x m(-2) x h(-1) in Sugar Creek and from 0 to 1300 micromol N x m(-2) x h(-1) in Iroquois River, the latter of which possesses greater streamflow discharge and a more homogeneous streambed and water column. Within the uncertainties of the two techniques, there is good agreement between the MIMS and IRMS results, which indicates that the production of N2 by the coupled process of nitrification/denitrification was relatively unimportant and surface-water NO3- was the dominant source of NO3- for benthic denitrification in these streams. Variation in stream NO3- concentration (from about 20 micromol/L during low discharge to 1000 micromol/L during high discharge) was a significant control of benthic denitrification rates, judging from the more abundant MIMS data. The interpretation that NO3- concentration directly affects denitrification rate was corroborated by increased rates of denitrification in cores amended with NO3-. Denitrification in Sugar Creek removed < or = 11% per day of the instream NO3- in late spring and removed roughly 15-20% in late summer. The fraction of NO3- removed in Iroquois River was less than that of Sugar Creek. Although benthic denitrification rates were relatively high during periods of high stream flow, when NO3 concentrations were also high, the increase in benthic denitrification could not compensate for the much larger increase in stream NO3- fluxes during high flow. Consequently, fractional NO3- losses were relatively low during high flow. PMID:17205897

Smith, Lesley K; Voytek, Mary A; Böhlke, John Karl; Harvey, Judson W

2006-12-01

318

Vibrational spectra and structure of RDX and its 13C- and 15N-labeled derivatives: a theoretical and experimental study.  

PubMed

Unambiguous vibrational band assignments have been made to cyclic nitramine hexahydro-1,3,5-trinitro-s-triazine, commonly known as the alpha-phase of RDX or alpha-RDX, with the use of (13)C and (15)N (on ring) enriched isotopic RDX analogues. Vibrational spectra were collected using Raman and IR spectroscopy in solid state and ab initio normal mode calculations were performed using density functional theory (DFT) and a 6-311G++** basis set. The calculated isotopic frequency shifts, induced by (13)C and (15)N labeling, are in very good accordance with measures ones. The changes in vibrational modes associated with the isotopic substitutions are well modeled by the calculation and previous assignments of the vibrational spectra have been revised, especially where the exact nature of the vibrational modes had been either vague or contradictory. PMID:20381411

Infante-Castillo, Ricardo; Pacheco-Londoño, Leonardo; Hernández-Rivera, Samuel P

2010-07-01

319

Localization of 15N uptake in a Tibetan alpine Kobresia pasture  

NASA Astrophysics Data System (ADS)

The Kobresia Pygmea ecotone covers approximately 450.000 km2 and is of large global and regional importance due several socio-ecological aspects. For instance Kobresia pastures store high amounts of carbon, nitrogen and other nutrients, represent large grazing areas for herbivores, provide a fast regrowth after grazing events and protect against mechanical degradation and soil erosion. However, Kobresia pastures are assumed to be a grazing induced and are accompanied with distinct root mats varying in thickness between 5-30 cm. Yet, less is known about the morphology and the functions of this root mats, especially in the background of a progressing degradation due to changes of climate and management. Thus we aimed to identify the importance of single soil layers for plant nutrition. Accordingly, nitrogen uptake from different soil depths and its remain in above-ground biomass (AGB), belowground biomass (BGB) and soil were determined by using a 15N pulse labeling approach during the vegetation period in summer 2012. 15N urea was injected into six different soil depths (0.5 cm, 2.5 cm, 7.5 cm, 12.5 cm, 17.5 cm, 22.5 cm / for each 4 replicates) and plots were sampled 45 days after the labeling. For soil and BGB samples were taken in strict sample intervals of 0-1 cm, 1-5 cm, 5-10 cm, 10-15 cm, 15-20 cm, 20-25 cm. Results indicate that total recovery (including AGB, BGB and soil) was highest, if tracer was injected into the top 5 cm and subsequently decreased with decreasing injection depth. This is especially the case for the 15N recovery of BGB, which is clearly attributed to the root density and strongly decreased with soil depth. In contrast, the root activity derived from the 15N content of roots increased with soil depth, which is primary associated to a proportionate increase of living roots related to dead roots. However, most 15N was captured in plant biomass (67.5-85.3 % of total recovery), indicating high 15N uptake efficiency possibly due to N limitation of Kobresia ecosystems. Considering only the nitrogen uptake of AGB hardly any differences appeared between the six injection depths. Nevertheless, it could be shown, that 50.4 % percent of total variance of AGB nitrogen uptake could be explained by combining root density and root activity. Concluding, from the upper root mat horizons highest amounts of nitrogen were taken up by plants, because root densities are correspondingly high. However, in deeper root mat layers the root activity increases and accordingly plays a key role for plant nitrogen supply in this depth. Underlying causes for increasing root activities may be better soil moisture conditions, lower variation of soil temperature and/or a higher access to plant available nitrogen in deeper soil layers.Please fill in your abstract text.

Schleuß, Per-Marten; Kuzyakov, Yakov

2014-05-01

320

Nitrate Reduction in a Groundwater Microcosm Determined by 15N Gas Chromatography-Mass Spectrometry  

PubMed Central

Aerobic and anaerobic groundwater continuous-flow microcosms were designed to study nitrate reduction by the indigenous bacteria in intact saturated soil cores from a sandy aquifer with a concentration of 3.8 mg of NO3?-N liter?1. Traces of 15NO3? were added to filter-sterilized groundwater by using a Darcy flux of 4 cm day?1. Both assimilatory and dissimilatory reduction rates were estimated from analyses of 15N2, 15N2O, 15NH4+, and 15N-labeled protein amino acids by capillary gas chromatography-mass spectrometry. N2 and N2O were separated on a megabore fused-silica column and quantified by electron impact-selected ion monitoring. NO3? and NH4+ were analyzed as pentafluorobenzoyl amides by multiple-ion monitoring and protein amino acids as their N-heptafluorobutyryl isobutyl ester derivatives by negative ion-chemical ionization. The numbers of bacteria and their [methyl-3H]thymidine incorporation rates were simultaneously measured. Nitrate was completely reduced in the microcosms at a rate of about 250 ng g?1 day?1. Of this nitrate, 80 to 90% was converted by aerobic denitrification to N2, whereas only 35% was denitrified in the anaerobic microcosm, where more than 50% of NO3? was reduced to NH4+. Assimilatory reduction was recorded only in the aerobic microcosm, where N appeared in alanine in the cells. The nitrate reduction rates estimated for the aquifer material were low in comparison with rates in eutrophic lakes and coastal sediments but sufficiently high to remove nitrate from an uncontaminated aquifer of the kind examined in less than 1 month.

Bengtsson, Goran; Annadotter, Helene

1989-01-01

321

Quantitative prediction of gas-phase 15N and 31P nuclear magnetic shielding constants  

NASA Astrophysics Data System (ADS)

High-level ab initio benchmark calculations of the 15N and 31P NMR chemical shielding constants for a representative set of molecules are presented. The computations have been carried out at the Hartree-Fock self-consistent field (HF-SCF), density functional theory (DFT) (B-P86 and B3-LYP), second-order Møller-Plesset perturbation theory (MP2), coupled cluster singles and doubles (CCSD), and CCSD augmented by a perturbative treatment of triple excitations [CCSD(T)] level of theory using basis sets of triple zeta quality or better. The influence of the geometry, the treatment of electron correlation, as well as basis set and zero-point vibrational effects on the shielding constants are discussed and the results are compared to gas-phase experimental shifts. As for the first time a study using high-level post-HF methods is carried out for a second-row element, we also propose a family of basis sets suitable for the computation of 31P shielding constants. The mean deviations observed for 15N and 31P are 0.9 [CCSD(T)/13s9p4d3f] and -3.3 ppm [CCSD(T)/15s12p4d3f2g], respectively, when corrected for zero-point vibrational effects. Results obtained at the DFT level of theory are of comparable accuracy to MP2 for 15N and of comparable accuracy to HF-SCF for 31P. However, they are not improved by inclusion of zero-point vibrational effects. The PN molecule is an especially interesting case with exceptionally large electron correlation effects on shielding constants beyond MP2 which, therefore, represents an excellent example for further benchmark studies.

Prochnow, Eric; Auer, Alexander A.

2010-02-01

322

Uptake of stormwater nitrogen in bioretention systems demonstrated from 15N tracer techniques  

NASA Astrophysics Data System (ADS)

Bioretention stormwater management systems are engineered ecosystems that capture urban stormwater in order to reduce the harmful effects of stormwater pollution on receiving waters. Bioretention systems have been shown to be effective at reducing the volume of runoff, and thereby reduce the nutrient loading to receiving waters from urban areas. However, little work has been done to evaluate the treatment processes that are responsible for reductions in effluent nitrogen (N). We hypothesize that the pulses of inorganic nitrogen associated with urban runoff events are captured in the plat tissues within these systems and not adsorbed to the soil media, thus creating a long-term, sustainable treatment approach to reducing the total nutrient loading to receiving waters. Nitrogen treatment performance was tested on two bioretention systems in Salt Lake City, UT: 1) an upland native community that does not require irrigation in semi-arid climates, and 2) a wetland community that requires 250 l of daily irrigation to offset the relatively high evaporative demand in the region. Each cell is sized to treat a 2.5 cm storm from a 140 m2 impervious surface: the area of the bioretention system is 10 m2. To test the N removal performance of each system, runoff events were simulated to represent an average precipitation regime using a synthetic stormwater blend starting in January, 2012. Effluent was collected from an underdrain and analyzed for total nitrogen (TN); mass removal was calculated for each month by subtracting the TN mass added to the garden minus the TN mass that flowed out of the garden. To test the hypothesis that plants assimilate stormwater N, 4 g of 100 atom% 15N NH4NO3 tracer was used as the N source in the synthetic stormwater during the first 2,000 l synthetic storm event in May. This isotopic label was calculated to enrich the total N pool of each garden to 100‰ 15N/14Nair. New growth was harvested from each plant in both cells and analyzed for 15N before the isotopic label was introduced and weekly thereafter. In May 2012, the upland garden captured 6.2 grams of TN from the added stormwater (55% of TN added), and the wetland garden captured 7.1 grams of TN from the added stormwater (67% of TN added). Within two weeks of adding the label, the 15N ratio increased 500‰ to 3,000‰ in all plant tissues tested in both systems. The results of the isotopic labeling experiment support the hypothesis that the plants used in both vegetated bioretention systems directly contribute to stormwater N treatment through N assimilation.

Houdeshel, D.; Hultine, K. R.; Pomeroy, C. A.

2012-12-01

323

Rotational dynamics of calcium-free calmodulin studied by 15N-NMR relaxation measurements.  

PubMed

The backbone motions of calcium-free Xenopus calmodulin have been characterized by measurements of the 15N longitudinal relaxation times (T1) at 51 and 61 MHz, and by conducting transverse relaxation (T2), spin-locked transverse relaxation (T1 rho), and 15N-[1H] heteronuclear NOE measurements at 61 MHz 15N frequency. Although backbone amide hydrogen exchange experiments indicate that the N-terminal domain is more stable than calmodulin's C-terminal half, slowly exchanging backbone amide protons are found in all eight alpha-helices and in three of the four short beta-strands. This confirms that the calcium-free form consists of stable secondary structure and does not adopt a 'molten globule' type of structure. However, the C-terminal domain of calmodulin is subject to conformational exchange on a time scale of about 350 microseconds, which affects many of the C-terminal domain residues. This results in significant shortening of the 15N T2 values relative to T1 rho, whereas the T1 rho and T2 values are of similar magnitude in the N-terminal half of the protein. A model in which the motion of the protein is assumed to be isotropic suggests a rotational correlation time for the protein of about 8 ns but quantitatively does not agree with the magnetic field dependence of the T1 values and does not explain the different T2 values found for different alpha-helices in the N-terminal domain. These latter parameters are compatible with a flexible dumb-bell model in which each of calmodulin's two domains freely diffuse in a cone with a semi-angle of about 30 degrees and a time constant of about 3 ns, whereas the overall rotation of the protein occurs on a much slower time scale of about 12 ns. The difference in the transverse relaxation rates observed between the amides in helices C and D suggests that the change in interhelical angle upon calcium binding is less than predicted by Herzberg et al. Strynadka and James [Strynadka, N. C. J. & James, M. N. G. (1988) Proteins Struct. Funct. Genet. 3, 1-17]. PMID:7601131

Tjandra, N; Kuboniwa, H; Ren, H; Bax, A

1995-06-15

324

Influenza A (H15N4) virus isolation in Western Siberia, Russia.  

PubMed

The rarely identified influenza A viruses of the H15 hemagglutinin subtype have been isolated exclusively in Australia. Here we report the isolation of an H15N4 influenza A virus (A/teal/Chany/7119/2008) in Western Siberia, Russia. Phylogenetic analysis demonstrated that the internal genes of the A/teal/Chany/7119/2008 strain belong to the Eurasian clade and that the H15 and N4 genes were introduced into the gene pool of circulating endemic avian influenza viruses through reassortment events. PMID:23283950

Sivay, Mariya V; Baranovich, Tatiana; Marchenko, Vasiliy Y; Sharshov, Kirill A; Govorkova, Elena A; Shestopalov, Aleksander M; Webby, Richard J

2013-03-01

325

Influenza A (H15N4) Virus Isolation in Western Siberia, Russia  

PubMed Central

The rarely identified influenza A viruses of the H15 hemagglutinin subtype have been isolated exclusively in Australia. Here we report the isolation of an H15N4 influenza A virus (A/teal/Chany/7119/2008) in Western Siberia, Russia. Phylogenetic analysis demonstrated that the internal genes of the A/teal/Chany/7119/2008 strain belong to the Eurasian clade and that the H15 and N4 genes were introduced into the gene pool of circulating endemic avian influenza viruses through reassortment events.

Sivay, Mariya V.; Baranovich, Tatiana; Marchenko, Vasiliy Y.; Sharshov, Kirill A.; Govorkova, Elena A.; Shestopalov, Aleksander M.

2013-01-01

326

Unusually negative nitrogen isotopic compositions (?15N) of mangroves and lichens in an oligotrophic, microbially-influenced ecosystem  

NASA Astrophysics Data System (ADS)

Extremes in (?15N values in mangrove tissues and lichens (range = +4 to -22‰) were measured from a mangrove forest ecosystem located on Twin Cays, offshore islands in Belize, Central America. The N isotopic compositions and concentrations of NH4+/NH3 in porewater, rainwater, atmospheric ammonia, mangrove leaves, roots, stems, and wood, and lichens, were examined to study the biogeochemical processes important for establishing these unusual N isotopic ratios. Porewater ammonium concentrations had little to no relationship to N isotopic fractionation in mangrove tissues. The ?15N of fine and coarse roots was 9‰ more positive than leaf tissue from the same tree. When P was added to dwarfed mangrove trees without added N, ?15N increased within one year to a &delta:15N closer to the &delta:15N of porewater ammonium (?15N=+4‰). Isotopically negative ammonia in the atmosphere (?15N=-18‰) and in rainwater (?15N=-9‰) were found on Twin Cays and may be sources of available N for isotopically depleted mangrove trees and lichens. In highly stressed, severely P limited trees, uptake of atmospheric N by Rhizophora mangle may be an important adaptive strategy.

Fogel, M. L.; Wooller, M. J.; Cheeseman, J.; Smallwood, B. J.; Roberts, Q.; Romero, I.; Jacobsen Meyers, M.

2008-02-01

327

15N isotopic analyses: a powerful tool to establish links between seized 3,4-methylenedioxymethamphetamine (MDMA) tablets.  

PubMed

In this study the (15)N/(14)N isotopic ratios of 43 samples of 3,4-methylenedioxymethamphetamine (MDMA) samples were measured using Gas Chromatography-Combustion-Isotope-Ratio Mass Spectrometry (GC-C-IRMS). The results show a large discrimination between samples with a range of delta(15)N values between -16 and +19 per thousand. Comparison between delta(15)N values and other physical and chemical parameters shows a strong relationship between delta(15)N and brand logo or composition. Thus, it could be assumed that tablets from different seizures probably originated from the same clandestine manufacturing source. Hence, (15)N isotopic parameters provide an important additional tool to establish common origins between seizures of clandestine synthetic drugs. PMID:12819848

Palhol, Fabien; Lamoureux, Catherine; Naulet, Norbert

2003-06-01

328

The perils and promises of microbial abundance: novel natures and model ecosystems, from artisanal cheese to alien seas.  

PubMed

Microbial life has been much in the news. From outbreaks of Escherichia coli to discussions of the benefits of raw and fermented foods to recent reports of life forms capable of living in extreme environments, the modest microbe has become a figure for thinking through the presents and possible futures of nature, writ large as well as small. Noting that dominant representations of microbial life have shifted from an idiom of peril to one of promise, we argue that microbes--especially when thriving as microbial communities--are being upheld as model ecosystems in a prescriptive sense, as tokens of how organisms and human ecological relations with them could, should, or might be. We do so in reference to two case studies: the regulatory politics of artisanal cheese and the speculative research of astrobiology. To think of and with microbial communities as model ecosystems offers a corrective to the scientific determinisms we detect in some recent calls to attend to the materiality of scientific objects. PMID:24941610

Paxson, Heather; Helmreich, Stefan

2014-04-01

329

Visualization of enantiomers using natural abundant (13)C-filtered single and double quantum selective refocusing experiments: Application to small chiral molecules.  

PubMed

The routine use of proton NMR for the visualization of enantiomers, aligned in the chiral liquid crystal solvent poly-gamma-benzyl-l-glutamate (PBLG), is restricted due to severe loss of resolution arising from large number of pair wise interaction of nuclear spins. In the present study, we have designed two experimental techniques for their visualization utilizing the natural abundance (13)C edited selective refocusing of single quantum (CH-SERF) and double quantum (CH-DQSERF) coherences. The methods achieve chiral discrimination and aid in the simultaneous determination of homonuclear couplings between active and passive spins and heteronuclear couplings between the excited protons and the participating (13)C spin. The CH-SERF also overcomes the problem of overlap of central transitions of the methyl selective refocusing (SERF) experiment resulting in better chiral discrimination. Theoretical description of the evolution of magnetization in both the sequences has been discussed using polarization operator formalism. PMID:19581115

Nath, Nilamoni; Baishya, Bikash; Suryaprakash, N

2009-09-01

330

Natural variations of /sup 13/C abundance in coal and bitumen as a tool to monitor co-processing  

SciTech Connect

The use of coal to facilitate the generation of transportation grade fuel bitumen, heavy oil for petroleum resids is a topic of continuing research. In order to optimize the upgrading process one needs to know in what proportion each feedstock contributes to each product fraction. Conventional analytical methods are neither able to distinguish the contribution from either feedstock in the synthetic products, nor measure the subtle changes in product character in response to differing process conditions. The inherent difference in the /sup 13/C//sup 12/C ratio between most coals and bitumens can be utilized as an isotopic tracer to assess the efficacy of co-processing. For example Vesta coal and Athabasca bitumen have sufficiently distinct /sup 13/C//sup 12/C ratios that the measured /sup 13/C//sup 12/C of any product will accurately reflect the proportion of feed incorporated into the product. From the elemental analysis and the /sup 13/C//sup 12/C ratio of the feedstock and products one can calculate the amount of carbon derived from coal (CDC) in each product fraction. Analogously the amount of bitumen derived carbon (BDC) can also be independently calculated. In this study the natural variation in /sup 13/C concentration was utilized as an isotopic tracer to evaluate co-processing efficiency of a one litre stirred autoclave under differing process conditions. Process variables examined were coal concentration, several iron based catalysts (Fe/sub 2/O/sub 3/; Fe/sub 2/O/sub 3/ impregnated with TiO/sub 2/, SnO/sub 2/, or ZnO and a sludge obtained from a nickel refinery) and temperature.

Muehlenbachs, K.; Steer, J.G. (Dept. of Geology, Univ. of Alberta, Edmonton Alberta, T6G 2E3 (CA)); Hogg, A. (Dept. of Chemistry, Univ. of Alberta, Edmonton Alberta T6G 2E3 (CA)); Ohuchi, T.; Beaulieu, G. (Coal Dept., Alberta Research Council, Devon, Alberta T0C 1E0 (CA))

1988-06-01

331

Natural variations of sup 13 C abundance in coal and bitumen as a tool to monitor coprocessing  

SciTech Connect

The use of coal to facilitate the generation of transportation grade fuel from bitumen, heavy oil or petroleum resids is a topic of continuing research. In order to optimize the upgrading process one needs to know in what proportion each feedstock contributes to each product fraction. Conventional analytical methods are neither able to distinguish the contribution from either feedstock in the synthetic products, nor measure the subtle changes in product character in response to differing process conditions. The inherent difference in the {sup 13}C/{sup 12}C ratio between most coals and bitumen can be utilized as an isotopic tracer to assess the efficacy of coprocessing. For example Vesta coal and Athabasca bitumen have sufficiently distinct {sup 13}C/{sup 12}C ratios that the measured {sup 13}C/{sup 12}C of any product will accurately reflect the proportion of feed incorporated into the product. From the elemental analysis and the {sup 13}C/{sup 12}C ratio of the feedstock and products one can calculate the amount of carbon derived from coal (CDC) in each product fraction. Analogously the amount of bitumen derived carbon (BDC) can also be independently calculated. In this study the natural variation in {sup 13}C concentration was utilized as an isotopic tracer to evaluate coprocessing efficiency of a one liter stirred autoclave under differing process conditions. Process variables examined were coal concentration, several iron based catalysts (Fe{sub 2}O{sub 3}; Fe{sub 2}O{sub 3} impregnated with TiO{sub 2}, SnO{sub 2}, or ZnO and a sludge obtained from a nickel refinery) and temperature.

Muehlenbachs, K.; Steer, J.G.; Hogg, A.; Ohuchi, T.; Beaulieu, G. (Univ. of Alberta, Edmonton (Canada))

1988-01-01

332

Measurement and interpretation of 15N-1H residual dipolar couplings in larger proteins  

PubMed Central

Summary A decade ago, Dr. L.E. Kay and co-workers described an ingenious HNCO-based triple resonance experiment from which several protein backbone RDCs can be measured simultaneously [1]. They implemented a J-scaling technique in the 15N dimension of the 3D experiment to obtain the NH RDCs. We have used this idea to carry out J-scaling in a 2D 15N-1H TROSY experiment and have found it to be an excellent method to obtain NH RDCs for larger proteins upto 70 kDa, far superior to commonly used HSQC in-phase/anti-phase and HSQC/TROSY comparisons. Here, this method, dubbed “RDC-TROSY” is discussed in detail and the limits of its utility are assessed by simulations. Prominent in the latter analysis is the evaluation of the effect of amide proton flips on the “RDC-TROSY” linewidths. The details of the technical and computational implementations of these methods for the determination of domain-orientations in 45–60 KDa Hsp70 chaperone protein constructs are described.

Bhattacharya, Akash; Revington, Matthew

2009-01-01

333

Contribution of 19F resonances on 18O(p,?)15N reaction rate  

NASA Astrophysics Data System (ADS)

The 18O(p,?)15N reaction influences the isotopes production such as 19F, 18O, and 15N which can be used to test the models of stellar evolution. 19F is synthesized in both asymptotic giant branch (AGB) and metal-rich Wolf-Rayet (WR) stars. Using R-matrix theory we allow new values of resonances parameters in 19F. We show that the most important contribution to the differential and total cross section at low energies, comes from the levels in 19F situated at resonances energies E R =151, 680 and 840 keV with spin and parity 1/2+. The total width of the 680 keV resonance is badly known. So, we have focused on this broad resonance corresponding to the 8.65 MeV level in 19F. We delimit the temperature range in which each resonance contribution to the total reaction rate occurs by analyzing the ratio (N A i /N A ). This allowed us to show that the 680 and 840 keV broad resonances strongly dominate the reaction rate over the stellar temperature range T 9=0.02-0.06 and T 9=0.5-5. Finally, these results were compared to NACRE and Iliadis astrophysical compilations.

Benmeslem, Meriem; Chafa, Azzedine; Barhoumi, Slimane; Tribeche, Mouloud

2014-05-01

334

Pathways for nitrate release from an alpine watershed: Determination using ??15N and ??18O  

USGS Publications Warehouse

[1] Snowpack, snowmelt, precipitation, surface water, and groundwater samples from the Loch Vale watershed in Colorado were analyzed for ??15N and ??18O of nitrate to determine the processes controlling the release of atmospherically deposited nitrogen from alpine and subalpine ecosystems. Although overlap was found between the ??15N(NO3) values for all water types (-4 to +6???), the ??18O(NO3) values for surface water and groundwater (+10 to +30???) were usually distinct from snowpack, snowmelt, and rainfall values (+40 to +70???). During snowmelt, ??18O(NO3) indicated that about half of the nitrate in stream water was the product of microbial nitrification; at other times that amount was greater than half. Springs emerging from talus deposits had high nitrate concentrations and a seasonal pattern in ??18O(NO3) that was similar to the pattern in the streams, indicating that shallow groundwater in talus deposits is a likely source of stream water nitrate. Only a few samples of surface water and groundwater collected during early snowmelt and large summer rain events had isotopic compositions that indicated most of the nitrate came directly from atmospheric deposition with no biological assimilation and release. This study demonstrates the value of the nitrate double-isotope technique for determining nitrogen-cycling processes and sources of nitrate in small, undisturbed watersheds that are enriched with inorganic nitrogen.

Campbell, D. H.; Kendall, C.; Chang, C. C. Y.; Silva, S. R.; Tonnessen, K. A.

2002-01-01

335

Measurement and interpretation of 15N- 1H residual dipolar couplings in larger proteins  

NASA Astrophysics Data System (ADS)

A decade ago, Dr. L.E. Kay and co-workers described an ingenious HNCO-based triple-resonance experiment from which several protein backbone RDCs can be measured simultaneously (Yang et al. (1999) [1]). They implemented a J-scaling technique in the 15N dimension of the 3D experiment to obtain the NH RDCs. We have used this idea to carry out J-scaling in a 2D 15N- 1H-TROSY experiment and have found it to be an excellent method to obtain NH RDCs for larger proteins upto 70 kDa, far superior to commonly used HSQC in-phase/anti-phase and HSQC/TROSY comparisons. Here, this method, dubbed "RDC-TROSY" is discussed in detail and the limits of its utility are assessed by simulations. Prominent in the latter analysis is the evaluation of the effect of amide proton flips on the "RDC-TROSY" linewidths. The details of the technical and computational implementations of these methods for the determination of domain orientations in 45-60 kDa Hsp70 chaperone protein constructs are described.

Bhattacharya, Akash; Revington, Matthew; Zuiderweg, Erik R. P.

2010-03-01

336

15N depleted nitrogen isotope values in Cretaceous black shales: paleoceanographic event or diagenesis.  

NASA Astrophysics Data System (ADS)

Nitrogen isotopic values of bulk sediment samples in black shales are almost exclusively near 0 ‰ and C/N ratios are high (20-35). Sequential extraction of exchangeable and non-exchangeable N fractions demonstrates that the inorganic N fraction is negligible and bulk sediment data reflect the organic N fraction. The trend in \\delta$15N and C/N has been observed in numerous localities and depositional environments in the mid-Cretaceous (Demarara Rise, DSDP Sites 367, 603B and 530, the Cretaceous Western Interior Seaway, Wunstorf, Germany, and Bahloul, Tunisia) as well as the Toarcian of England and in Quaternary Mediterranean Sapropels. Three explanations are considered: 1) That primary production during black shale deposition was dominated by a unique community composed of nitrogen-fixing cyanobacteria; or 2) utilization of a 15N depleted ammonium source by another set of biota; or 3) that the values are the result of diagenetic loss of N prevailing in Corg-rich strata with a low capacity for N adsorption. The depleted nitrogen isotopic values suggest that nitrogen fixation or utilization of a depleted nitrogen source (e.g. ammonium) may have been important which is plausible in consideration of nitrogen deficiencies that might characterize widespread deep-water anoxia. Secular variations in nitrogen isotope values across the Cenomanian-Turonian Boundary of ODP Site 1261, Demarara Rise, show a shift from -1 to -3‰ . One interpretation of the origin of the excursion could be that a fraction of the organic matter was produced utilizing a 15N depleted ammonium source, assuming that the nitrogen isotopic composition of fixed oceanic nitrogen does not change. However, it should be noted that large (greater than 1‰ ) variations in nitrogen isotope values are observed above and below the Cenomanian-Turonian Boundary Event and have no known paleoceanographic forcing. The variations in nitrogen isotope values are matched by antithetic variations in C/N indicating diagenetic N-loss that could be interpreted as the primary control on the nitrogen isotope variations. The high C/N ratios probably result from selective removal of N-enriched compounds in the water column and during burial diagenesis. Clay-poor, Corg-rich sediments have a low sorptive capacity, allowing diffusion of dissolved N out of the Corg-rich sediments resulting in higher C/N ratios. Pore water ammonium concentrations are mM, indicating low sorption and high rates of diffusion into overlying strata. Coupled C/N and N-isotope variations occur by the removal of a 15N enriched fraction. Protein degradation has been suggested to result in negative isotopic shifts but would not result in large increases in C/N and the isotopic shifts are limited by the protein richness of the primary organic matter and the internal isotopic heterogeneity of the organic matter pools. Although we favor an explanation that involves a primary signature, diagenesis cannot be excluded in low ? 15N values.

Junium, C. K.; Arthur, M. A.

2004-12-01

337

Changes in Natural Abundance Carbon Stable isotopes of Human Blood and Saliva After 24 Days of Controlled Carbohydrate Supplementation  

NASA Astrophysics Data System (ADS)

With the advent of corporate agriculture, large-scale economic decisions have given rise to unique global environmental effects. Emphasis on corn production results in dramatic changes in nitrogen and water cycling via the intensive cultivation practices necessary to support Zea mays (Tilman, 1998). In particular, consumption of corn derived food additive high-fructose corn syrup (HFCS) has increased more than 1000% since 1970 and may be associated with the epidemics of obesity and diabetes (Bray et al., 2004). Plausible mechanisms for an adverse effect of fructose load on glucose homeostasis have been proposed (Havel, 2005). The unusually heavy 13C signature of corn, as compared to other plants, offers the opportunity to develop a biomarker for sugar consumption. Among the many experiments that are needed to establish such a technique, the demonstration of change in 13C signature of human tissues with known change in carbohydrate consumption is foremost. Here we report on a controlled feeding study performed in cooperation with the United States Department of Agriculture (USDA), to test the effect of supplementation of human diet with carbohydrate of known ?13C value. During this study, 13 individuals were fed a typical American diet (32% calories from fat, 15% calories from protein, 53% carbohydrate) for ~six months. Each participant was fed a random sequence of carbohydrate supplements (50 grams of supplement per day): 1. resistant maltodextrin (?13C = -10.59‰); 2. maltodextrin (?13C = -23.95‰); 3. a 50-50 mixture of the two (?13C = -15.94‰). After 24 days of feeding, subjects showed enrichment in blood serum that was significantly correlated (p = 0.0038) with the ?13C value of the supplement. However, blood clot and saliva showed no such correlation, suggesting that the half-lives of these substrates may render them unsuitable for carbohydrate dietary reconstruction over day-to-month timescales. All subjects of the study showed a net enrichment in the ?13C value of their blood and saliva relative to baseline: blood clot was enriched by 0.27‰; blood serum by 0.50‰ and saliva by 1.12‰. We believe this overall enrichment resulted from a 13C-enriched bulk diet (?13C = - 20.42‰) relative to the subjects free-living diet. Evidence for this derives from inspection of foods within the bulk diet provided, compared to published profiles of the typical American diet. We will discuss possible complicating factors, such as differential absorption and metabolism of the supplements according to solubility and caloric value. These results are encouraging for the development of a ?13C blood serum biomarker that, in the company of other tests, could be used to indicate a change in carbohydrate intake. Bray, G.A., Nielsen, S.J. and Popkin, B.M., 2004. Consumption of high-fructose corn syrup in beverages may play a role in the epidemic of obesity. American Journal of Clinical Nutrition, 79: 537-543. Havel, P.J., 2005. Dietary fructose: Implications for dysregulation of energy homeostasis and lipid/carbohydrate metabolism. Nutrition Reviews, 63(5): 133-157. Tilman D., 1998. The greening of the green revolution. Nature, 396:211-212.

Kraft, R. A.; Jahren, A. H.; Baer, D. J.; Caballero, B.

2008-12-01

338

13C and 15N allocations of two alpine species from early and late snowmelt locations reflect their different growth strategies  

PubMed Central

Intense efforts are currently devoted to disentangling the relationships between plant carbon (C) allocation patterns and soil nitrogen (N) availability because of their consequences for growth and more generally for C sequestration. In cold ecosystems, only a few studies have addressed whole-plant C and/or N allocation along natural elevational or topographical gradients. 12C/13C and 14N/15N isotope techniques have been used to elucidate C and N partitioning in two alpine graminoids characterized by contrasted nutrient economies: a slow-growing species, Kobresia myosuroides (KM), and a fast-growing species, Carex foetida (CF), located in early and late snowmelt habitats, respectively, within the alpine tundra (French Alps). CF allocated higher labelling-related 13C content belowground and produced more root biomass. Furthermore, assimilates transferred to the roots were preferentially used for growth rather than respiration and tended to favour N reduction in this compartment. Accordingly, this species had higher 15N uptake efficiency than KM and a higher translocation of reduced 15N to aboveground organs. These results suggest that at the whole-plant level, there is a compromise between N acquisition/reduction and C allocation patterns for optimized growth.

Baptist, Florence; Tcherkez, Guillaume; Aubert, Serge; Pontailler, Jean-Yves; Choler, Philippe; Nogues, Salvador

2009-01-01

339

The effect of FISH and CARD-FISH on the isotopic composition of (13)C- and (15)N-labeled Pseudomonas putida cells measured by nanoSIMS.  

PubMed

The use of nanoSIMS for the exploration of microbial activities in natural habitats often implies that stable isotope tracer experiments are combined with in situ hybridization techniques (i.e. fluorescence in situ hybridization (FISH) or catalyzed reporter deposition (CARD)-FISH). In this study, Pseudomonas putida grown on (13)C- and (15)N-labeled carbon and nitrogen, collected in exponential growth and stationary phases, was hybridized and analyzed by nanoSIMS. It was shown that (13)C and (15)N fractions decreased after FISH and CARD-FISH in comparison to chemically untreated cells. However, the fractions were influenced differently by various treatments. After paraformaldehyde fixation of exponentially growing cells, a reduction of the (13)C and (15)N fractions was measured from 94±1.2% and 89.5±3.8% to 90.2±0.8% and 64±4.6%, respectively, indicating that nitrogen isotopic composition was most influenced. A further decrease of the (13)C and (15)N fractions to 80.7±6.5 and 59.5±4.1%, respectively, was measured after FISH, while CARD-FISH decreased the fractions to 57.4±3.0% and 47.1±4.1%, respectively. The analysis of cells collected in different growth phases revealed that the effect of various treatments seemed to be dependent on the cell's physiological state. In addition, a mathematical model that can be used in further studies was developed in order to calculate the amount of carbon introduced into the cells by chemical treatments. These results can be valuable for environmental FISH-nanoSIMS studies where the isotopic composition of single cells will be used to quantitatively assess the importance of specific populations to certain biochemical processes and determine budget estimations. PMID:24702905

Musat, Niculina; Stryhanyuk, Hryhoriy; Bombach, Petra; Adrian, Lorenz; Audinot, Jean-Nicolas; Richnow, Hans H

2014-06-01

340

1 H, 13 C, and 15 N backbone, side-chain, and heme chemical shift assignments for oxidized and reduced forms of the monoheme c -type cytochrome ApcA isolated from the acidophilic metal-reducing bacterium Acidiphilium cryptum  

Microsoft Academic Search

We report the 1H, 13C, and 15N chemical shift assignments of both oxidized and reduced forms of an abundant periplasmic c-type cytochrome, designated ApcA, isolated from the acidophilic gram-negative facultatively anaerobic metal-reducing alphaproteobacterium\\u000a Acidiphilium cryptum. These resonance assignments prove that ApcA is a monoheme cytochrome c\\u000a 2 and the product of the Acry_2099 gene. An absence of resonance peaks in

John R. CortMichael; Michael W. Swenson; Timothy S. Magnuson

2011-01-01

341

Sample Artefacts in ?15N and ?18O of Nitrate in the atmosphere  

NASA Astrophysics Data System (ADS)

Nitrate is one of the major inorganic anions in aerosols. Recently nitrogen and oxygen isotopes in nitrates have been used to trace sources and chemical processes in the atmosphere. High volume samplers are used in order to gain enough material for isotope analysis, but artefacts can occur when measuring with this technique. Besides retaining NO3 from aerosol, gaseous HNO3 can be absorbed on the filter increasing the reported values of nitrate reported. Alternatively; when elevated temperatures are present in the atmosphere, nitrate is volatized in the form of NH3NO3 which would lead to an underestimation of nitrogen on the filter [Schaap et al., 2004]. The artefacts from high volume sampling may cause inaccuracies in the reported isotope values due to isotope fractionation or different initial isotope values between gaseous HNO3 and particulate nitrate. High volume samplers were deployed on board a ship in the summer of 2003 jointly with the Canadian Surface Ocean - Lower Atmosphere Study (SOLAS). A quartz filter was positioned on a high volume sampler. A cellulose acetate filter treated with potassium carbonate and glycerol was placed underneath the quartz filter. The cellulose acetate filter is designed to catch sticky gaseous (such as SO2) but was also found to catch a nitrogen gas species (most probable HNO3 and/or NH3NO3). Analysis of isotopic composition of nitrate for both nitrogen and oxygen was carried out on selected samples by the denitrifier method. Values ranged between -4 and +1‰ for ?15N and between +49 and +66‰ for ?18O for quartz filter. The nitrogen gas species had ranges between -11 and -0‰ for ?15N and between +44 and +62‰ for ?18O. Average differences between the aerosol (caught on the quartz filter) and the nitrogen gas species (on the cellulose acetate filter) were 3±4 ‰ for ?15N and 10±7 ‰ for ?18O. These values are examined to find insights in possible fractionation in the nitrate collection method currently used in other studies. Schaap, M., G. Spindler, M. Schulz, K. Acker, W. Maenhaut, A. Berner, W. Wieprecht, N. Streit, K. Müller, E. Brüggemann, X. Chi, J.-P. Putaud, R. Hitzenberger, H. Puxbaum, U. Baltensperger and H. ten Brink (2004), Artefacts in the sampling of nitrate studied in the “INTERCOMP” campaigns of EUROTRAC-AEROSOL, Atmospheric Environment, 38, 6487-6496.

Seguin, A.; Norman, A. L.

2009-12-01

342

Diffusion technique for 15N and inorganic N analysis of low-N aqueous solutions and Kjeldahl digests.  

PubMed

Diffusion of ammonia is a common sample preparation method for the stable isotope analysis of inorganic nitrogen in aqueous solution. Classical diffusion methods usually require 6-12 days of diffusion and often focus on (15)N/(14)N analysis only. More recent studies have discussed whether complete N recovery was necessary for the precise analysis of stable N isotope ratios. In this paper we present a newly revised diffusion technique that allows correct and simultaneous determination of total N and (15)N at% from aqueous solutions and Kjeldahl digests, with N concentrations down to sub-0.5-mg N L(-1) levels, and it is tested under different conditions of (15)N isotope labelling. With the modification described, the diffusion time was reduced to 72 h, while the ratios of measured and expected (15)N at% were greater than 99% and the simultaneous recovery of total N was >95%. Analysis of soil microbial biomass N and its (15)N/(14)N ratio is one of the most important applications of this diffusion technique. An experiment with soil extracts spiked with (15)N-labelled yeast showed that predigestion was necessary to prevent serious N loss during Kjeldahl digestion of aqueous samples (i.e. soil extracts). The whole method of soil microbial biomass N preparation for (15)N/(14)N analysis included chloroform fumigation, predigestion, Kjeldahl digestion and diffusion. An experiment with soil spiked with (15)N-labelled yeast was carried out to evaluate the method. Results showed a highly significant correlation of recovered and added N, with the same recovery rate (0.21) of both total N and (15)N. A k(N) value of 0.25 was obtained based on the data. In conclusion, the diffusion method works for soil extracts and microbial biomass N determination and hence could be useful in many types of soil/water studies. PMID:18438764

Chen, Rui Rui; Dittert, Klaus

2008-06-01

343

?13C and ?15N in the ornithogenic sediments from the Antarctic maritime as palaeoecological proxies during the past 2000 yr  

NASA Astrophysics Data System (ADS)

In this paper, we have examined carbon and nitrogen isotopic compositions in two ornithogenic sediment profiles from the Ardley Island and Barton Peninsula of Antarctica for palaeoecological changes during the past 2000 yr. The ?13C values of the two sediment profiles range from - 22.26‰ to - 19.15‰ (PDB) in Core G and from - 24.01‰ to - 19.87‰ in profile A, showing that the predominant carbon source in the sediments plausibly comes from terrestrial and aquatic plants in Antarctic such as mosses, lichens, and algae in lakes. As these ?13C values are also close to those in the fresh lake sediments that are not influenced by penguin guano, one may not use the ?13C values as evidence for the influence of guano on the sediments. The ?15N values of the two profiles range from 4.75‰ to 18.34‰ (air) and from 5.17‰ to 10.38‰ for Core G and Core A, respectively. The ?15N variations have positive correlations with the trends of the bio-element contents in the sediments. As the levels of these bio-elements in ornithogenic sediments had been used to reconstruct the changes of historical penguin population and tundra vegetation abundance and diversity, we then suggest that the ?15N records can be utilized to study palaeoecological processes of penguin. Our results show that penguin population and activity has generally decreased over the past 2000 yr. From 1300 to 900 yr BP and from 1790 to 1860 AD, penguin population and activity experienced two strong decreases. It will be interesting to understand the cause of these decreases.

Liu, Xiao-Dong; Li, Hong-Chun; Sun, Li-Guang; Yin, Xue-Bin; Zhao, San-Ping; Wang, Yu-Hong

2006-03-01

344

(1)H, (13)C and (15)N resonance assignments of the Onconase FL-G zymogen.  

PubMed

Onconase(®) FL-G zymogen is a 120 residue protein produced by circular permutation of the native Onconase(®) sequence. In this construction, the wild type N- and C-termini are linked by a 16 residue segment and new N- and C-termini are generated at wild type positions R73 and S72. This novel segment linking the native N- and C-termini is designed to obstruct Onconase's(®) active site and encloses a cleavage site for the HIV-1 protease. As a first step towards the resolution of its 3D structure and the study of its structure-function relationships, we report here the nearly complete NMR (1)H, (13)C and (15)N resonance chemical shift assignments at pH 5.2 and 35°C (BMRB deposit no 17973). The results presented here clearly show that the structure of the wild type Onconase(®) is conserved in the FL-G zymogen. PMID:22392335

Serrano, Soraya; Callís, Mariona; Vilanova, Maria; Benito, Antoni; Laurents, Douglas V; Ribó, Marc; Bruix, Marta

2013-04-01

345

Tandem mass spectrometric investigation of acylpolyamines of spider venoms and their 15N-labeled derivatives.  

PubMed

The fragmentation mechanism of the acylpentamine toxins 1-4 found in the venom of the spider Agelenopsis aperta has been investigated in detail. To identify the origin of the two doublets of unexpected fragment ions at m/z 129/112 and m/z 115/98, three synthetic 15N-labeled analogs 5-7 have been prepared and subjected to CID fragmentation on a triple quadrupole mass spectrometer. It appears that the unexpected doublet of fragment ions arises from an internal portion of the polyamine backbone after either a transaminative Zip reaction or a sequential fragmentation of the quasi-molecular ion. The second option has been proven by in-source CID experiments. The detailed knowledge of acylpentamine fragmentation mechanisms is essential for the correct characterization of isomeric compounds, particularly for coeluting compounds within complex mixtures such as spider venoms. PMID:15519231

Tzouros, Manuel; Manov, Nikolay; Bienz, Stefan; Bigler, Laurent

2004-11-01

346

High-resolution Fourier-transform extreme ultraviolet photoabsorption spectroscopy of 14N15N  

NASA Astrophysics Data System (ADS)

The first comprehensive high-resolution photoabsorption spectrum of 14N15N has been recorded using the Fourier-transform spectrometer attached to the Desirs beamline at the Soleil synchrotron. Observations are made in the extreme ultraviolet and span 100 000-109 000 cm-1 (100-91.7 nm). The observed absorption lines have been assigned to 25 bands and reduced to a set of transition energies, f values, and linewidths. This analysis has verified the predictions of a theoretical model of N2 that simulates its photoabsorption and photodissociation cross section by solution of an isotopomer independent formulation of the coupled-channel Schrödinger equation. The mass dependence of predissociation linewidths and oscillator strengths is clearly evident and many local perturbations of transition energies, strengths, and widths within individual rotational series have been observed.

Heays, A. N.; Dickenson, G. D.; Salumbides, E. J.; de Oliveira, N.; Joyeux, D.; Nahon, L.; Lewis, B. R.; Ubachs, W.

2011-12-01

347

Creating 13C- and 15N-enriched tree leaf litter for decomposition experiments  

NASA Astrophysics Data System (ADS)

Labeling plant material with heavy isotopes of carbon and nitrogen can produce a traceable nutrient signal that can be followed into the different trophic levels and decomposer food web. We treated 60 tree saplings with 13C-enriched CO2 gas and 15N-enriched ammonium nitrate over a three-month period to create dually-labeled plant material for future decomposition experiments. The trees included both early (Red maple, Sweetgum, Tulip poplar) and late (American beech, White oak) successional deciduous tree species, and a conifer, White pine. We constructed a 2.4 m × 2.4 m × 2.4 m environmental chamber that was climate-controlled using an air conditioning system. An Arduino microcontroller interfaced with a Vaisala GMP343 CO2 probe maintained a CO2 concentration between 500-520 ppm by controlling a solenoid valve on the CO2 tank regulator. The trees were placed into the chamber in August 2012 and remained until senescence unless they were lost to death or disease. Ammonium nitrate was added twice, in September and October. Leaf samples were collected prior to the start of the experiment and after senescence, whereas root samples were collected only in December. Samples were dried, ground and analyzed using an isotope ratio mass spectrometer. American beech and White oak had 40% mortality, and 34% of tulip poplar trees were removed because of powdery mildew overgrowth or death. Most tulip poplar trees exhibited a second leaf out following senescence in late September. Nearly 1 kg of litter was produced with tulip poplar representing over half of the total mass. Levels of enrichment varied greatly by species. Beech (-14.2‰) and White oak (-4.8‰) had low levels of enrichment in comparison to early successional species such as Sweetgum (41.7‰) and Tulip poplar (30.7‰ [first leaf fall] and 238.0‰ [second leaf fall]). Leaf enrichment with 15N followed a similar pattern, though it was achieved at a higher level with ?15N values varying from 271.6‰ to 1354.2‰ at the end of the experiment. Enrichment of roots was significantly higher than leaves (?13C range: 111.5-219.2‰; ?15N range: 1516.9-3939.3‰) indicating that nutrients were translocated away from leaves prior to senescence, which is supported by the increase in C:N ratio between the initial (19.0) and final (60.1) leaf sampling. Despite the variable levels of enrichment, leaves from all species were sufficiently labeled for use in future studies aimed at tracking the transformation of carbon and nitrogen during decomposition. The greatest challenges were treating diseases and pests and creating ideal growing conditions for many species within the same chamber. Reducing the number of individuals and better pest management will lead to even higher level enrichment in the future.

Szlavecz, K. A.; Pitz, S.; Chang, C.; Bernard, M.

2013-12-01

348

/sup 15/N and /sup 13/C NMR determination of methionine metabolism in developing soybean cotyledons  

SciTech Connect

The metabolism of D- and L-methionine by immature cotyledons of soybean (Glycine max, L. cv Elf) grown in culture has been investigated using solid-state /sup 13/C and /sup 15/N nuclear magnetic resonance. D-Methionine is taken up by the cotyledons and converted to an amide, most likely by N-malonylation. About 16% of the L-methionine taken up is incorporated intact into protein, and 25% remains as soluble methionine. Almost two-thirds of the L-methionine that enters the cotyledons is degraded. The largest percentage of this is used in transmethylation of the carboxyl groups of pectin. Methionine is not extensively converted to polyamines. The authors attribute the stimulation of growth of the cotyledons by exogenous methionine to the bypassing of a rate-limiting methyl-transfer step in the synthesis of methionine itself, and subsequently of pectins and proteins.

Coker, G.T. III; Garbow, J.R.; Schaefer, J.

1987-03-01

349

Experimental and calculated 1H, 13C, 15N NMR spectra of famotidine  

NASA Astrophysics Data System (ADS)

Famotidine, 3-[[[2-[(aminoiminomethyl)amino]-4-thiazolyl]methyl]thio]- N-(aminosulfonyl), is a histamine H 2-receptor blocker that has been used mainly for the treatment of peptic ulcers and the Zollinger-Ellison syndrome. Its NMR spectra in different solvents were reported earlier; however, detailed interpretation has not been done thus far. In this work, experimental 1H, 13C and 15N NMR spectra of famotidine dissolved in DMSO-d 6 are shown. The assignment of observed chemical shifts is based on quantum chemical calculation at the Hartree-Fock/6-31G ? level. The geometry optimization of the famotidine molecule with two internal hydrogen bonds, i.e. [N(3)-H(23)⋯N(9) and N(3)⋯H(34)-N(20)], is done by using the B3LYP method with the 6-31G ? basis set.

Bara?ska, M.; Czarniecki, K.; Proniewicz, L. M.

2001-05-01

350

The Pure Rotational Spectra of Acetaldehyde and Glycolaldehyde Isotopologues Measured in Natural Abundance by Chirped-Pulse Fourier Transform Microwave Spectroscopy  

NASA Astrophysics Data System (ADS)

Complex organic molecules (COMs) such as glycolaldehyde (HOCH_2CHO) and acetaldehyde (CH_3CHO) have now been detected in numerous interstellar sources. Glycolaldehyde has been detected in two hot cores, Sgr B2(N) and G31.41+0.31. Acetaldehyde has been observed in various sources, including the translucent clouds CB 17 and CB 24, cold molecular clouds such as TMC-1 and L134N, and hot cores such as Sgr B2(N), NGC 6334F, and the Orion Compact Ridge. Such COMs are known to have rich and complex spectra that add to the line confusion problem faced in observations of molecule-rich sources. Laboratory studies of excited vibrational states and isotopologues for known COMs therefore provide important guidance for sorting out the interstellar line confusion problem. Detection of isotopologues and determination of their abundance relative to the main isotopic species would also provide important constraints on interstellar chemical models, as these isotopic ratios are dependent on the formation mechanism for each species. The isotopic ratios for 13C/12C, 18O/16O, and D/H are known in various interstellar environments for simple molecules, but remain relatively unexplored for more complex species such as glycolaldehyde and acetaldehyde. The rotational spectra of the main isotopologues for glycolaldehyde and acetaldehyde have been well-characterized through microwave, millimeter, and submillimeter laboratory spectroscopy. Here we present the laboratory characterization of the isotopologues of acetaldehyde and glycolaldehyde in natural abundance by chirped pulse Fourier transform microwave spectroscopy (CP-FTMW). This spectroscopic information lays the groundwork for additional higher-frequency studies that can be directly applied to the interpretation of millimeter and submillimeter observations.

Carroll, P. Brandon; McGuire, Brett A.; Weaver, Susanna L. Widicus; Zaleski, Daniel P.; Neill, Justin L.; Pate, Brooks H.

2011-06-01

351

Cosine Modulated HSQC: A Rapid Determination of 3JHNH? Scalar Couplings in 15N-labeled Proteins  

NASA Astrophysics Data System (ADS)

A two-dimensional HSQC-based NMR method, 15N-COSMO-HSQC, is presented for the rapid determination of homonuclear 3JHNH? couplings in 15N-labeled proteins in solution. Scalar couplings are extracted by comparing the intensity of two separate datasets recorded with and without decoupling of the 3JHNH? during a preparation period. The scalar couplings are introduced through a cosine modulation of the peak intensities. The experiment relies on a BIRD sandwich to selectively invert all amide protons H N and is very simple to implement. 3JHNH? couplings were determined using both the 15N-COSMO-HSQC and quantitative- J on 15N-labeled chemokine RANTES. The two experiments show well-correlated values.

Petit, Audrey; Vincent, Sébastien J. F.; Zwahlen, Catherine

2002-06-01

352

Proton-decoupled CPMG: A better experiment for measuring 15N R2 relaxation in disordered proteins  

NASA Astrophysics Data System (ADS)

15N R2 relaxation is one of the most informative experiments for characterization of intrinsically disordered proteins (IDPs). Small changes in nitrogen R2 rates are often used to determine how IDPs respond to various biologically relevant perturbations such as point mutations, posttranslational modifications and weak ligand interactions. However collecting high-quality 15N relaxation data can be difficult. Of necessity, the samples of IDPs are often prepared with low protein concentration and the measurement time can be limited because of rapid sample degradation. Furthermore, due to hardware limitations standard experiments such as 15N spin-lock and CPMG can sample the relaxation decay only to ca. 150 ms. This is much shorter than 15N T2 times in disordered proteins at or near physiological temperature. As a result, the sampling of relaxation decay profiles in these experiments is suboptimal, which further lowers the precision of the measurements.

Yuwen, Tairan; Skrynnikov, Nikolai R.

2014-04-01

353

Diatom-bound 15N\\/14N: New support for enhanced nutrient consumption in the ice age subantarctic  

Microsoft Academic Search

Diatom-bound 15N\\/14N was used to reconstruct the glacial nutrient status of the Subantarctic Zone in the Southern Ocean. Down-core records from both the Pacific and Indian sectors show ?15N of 5 to 6‰ during the Last Glacial Maximum and a decrease, coincident with the glacial termination, to values as low as 2‰. The effect of either diatom assemblage or physiological

Rebecca S. Robinson; Daniel M. Sigman; Peter J. DiFiore; Melissa M. Rohde; Tracy A. Mashiotta; David W. Lea

2005-01-01

354

Transformations in soil and availability to plants of 15 N applied as inorganic fertilizer and legume residues  

Microsoft Academic Search

Summary A pot experiment was conducted to study the transformations of organic and inorganic N in soil and its availability to maize plants. Inorganic N was in the form of15N labelled ammonium sulphate (As) and15N labelledSesbania aculeata (Sa), a legume, was used as organic N source. Plants utilized 20% of the N applied as As; presence of Sa reduced the

F. Azam; K. A. Malik; M. I. Sajjad

1985-01-01

355

? 15N and ? 13C dynamics of suspended organic matter in freshwater and brackish waters of the Scheldt estuary  

Microsoft Academic Search

Suspended particulate organic matter was sampled monthly between June 1999 and April 2000 in the Scheldt river and estuary to investigate the seasonal and spatial patterns of ?13C and ?15N signatures. ?15N of suspended matter showed large seasonal variation. Minimum values ranged from ?0.5‰ in the freshwater zone (spring situation) to +2.3‰ in the mesohaline zone (winter situation). Maximum values

L. De Brabandere; F. Dehairs; S. Van Damme; N. Brion; P. Meire; N. Daro

2002-01-01

356

Dynamics of soil microbial biomass N under zero and shallow tillage for spring wheat, using 15 N urea  

Microsoft Academic Search

Summary Field studies to determine the effect of zero and shallow (10 cm) cultivation on microbial biomass were conducted on several Chernozemic soils in western Canada. Using the CHCl3 fumigation method, the distribution of microbial biomass N and the immobilization and subsequent release of added15N (15N-urea) from the microbial biomass were determined in the A horizon, at the 0 to

M. R. Carter; D. A. Rennie

1984-01-01

357

Longitudinal distribution of nitrate ? 15 N and ? 18 O in two contrasting tropical rivers: implications for instream nitrogen cycling  

Microsoft Academic Search

The longitudinal variations in the nitrogen (?15N) and oxygen (?18O) isotopic compositions of nitrate (NO3\\u000a ?), the carbon isotopic composition (?13C) of dissolved inorganic carbon (DIC) and the ?13C and ?15N of particulate organic matter were determined in two Southeast Asian rivers contrasting in the watershed geology and land\\u000a use to understand internal nitrogen cycling processes. The $$ \\\\delta^{15} {\\\\text{N}}_{{{\\\\text{NO}}_{3}

Toshihiro Miyajima; Chikage Yoshimizu; Yoshie Tsuboi; Yoshiyuki Tanaka; Ichiro Tayasu; Toshi Nagata; Isao Koike

2009-01-01

358

Conformation of Alamethicin in Oriented Phospholipid Bilayers Determined by 15N Solid-State Nuclear Magnetic Resonance  

Microsoft Academic Search

The conformation of the 20-residue antibiotic ionophore alamethicin in macroscopically oriented phospholipid bilayers has been studied using 15N solid-state nuclear magnetic resonance (NMR) spectroscopy in combination with molecular modeling and molecular dynamics simulations. Differently 15N-labeled variants of alamethicin and an analog with three of the ?-amino-isobutyric acid residues replaced by alanines have been investigated to establish experimental structural constraints and

Mads Bak; Robert P. Bywater; Morten Hohwy; Jens K. Thomsen; Kim Adelhorst; Hans J. Jakobsen; Ole W. Sørensen; Niels C. Nielsen

2001-01-01

359

Homogeneity of delta(15)N in needles of Masson pine (Pinus massoniana L.) was altered by air pollution.  

PubMed

The present study investigated the changes of delta(15)N values in the tip, middle and base section (divided by the proportion to needle length) of current- and previous-year needles of Masson pine (Pinus massoniana L.) from two declining forest stands suffering from air pollution, in comparison with one healthy stand. At the healthy stand, delta(15)N in the three sections of both current- and previous-year needles were found evenly distributed, while at the polluted stands, delta(15)N values in the needles were revealed significantly different from the tip to the base sections. The results implied that the distribution of delta(15)N among different parts or sections in foliages was not always homogeneous and could be affected by air pollution. We suggested that the difference of delta(15)N values among pine needle sections should be reconsidered and should not be primarily ignored when the needle delta(15)N values were used to assess plant responses to air pollution. PMID:19897291

Kuang, Yuan Wen; Wen, Da Zhi; Li, Jiong; Sun, Fang Fang; Hou, En Qing; Zhou, Guo Yi; Zhang, De Qiang; Huang, Long-bin

2010-05-01

360

Mycorrhizal fungi supply nitrogen to host plants in Arctic tundra and boreal forests: 15N is the key signal.  

PubMed

Symbiotic fungi's role in providing nitrogen to host plants is well-studied in tundra at Toolik Lake, Alaska, but little-studied in the adjoining boreal forest ecosystem. Along a 570 km north-south transect from the Yukon River to the North Slope of Alaska, the 15N content was strongly reduced in ectomycorrhizal and ericoid mycorrhizal plants including Betula, Salix, Picea mariana (P. Mill.) B.S.P., Picea glauca Moench (Voss), and ericaceous plants. Compared with the 15N content of soil, the foliage of nonmycorrhizal plants (Carex and Eriophorum) was unchanged, whereas content of the ectomycorrhizal fungi was very much higher (e.g., Boletaceae, Leccinum and Cortinarius). It is hypothesized that similar processes operate in tundra and boreal forest, both nitrogen-limited ecosystems: (i) mycorrhizal fungi break down soil polymers and take up amino acids or other nitrogen compounds; (ii) mycorrhizal fungi fractionate against 15N during production of transfer compounds; (iii) host plants are accordingly depleted in 15N; and (iv) mycorrhizal fungi are enriched in 15N. Increased N availability for plant roots or decreased light availability to understory plants may have decreased N allocation to mycorrhizal partners and increased delta15N by 3-4 parts per million for southern populations of Vaccinium vitis-idaea L. and Salix. Fungal biomass, measured as ergosterol, correlated strongly with soil organic matter and attained amounts similar to those in temperate forest soils. PMID:19190704

Hobbie, John E; Hobbie, Erik A; Drossman, Howard; Conte, Maureen; Weber, J C; Shamhart, Julee; Weinrobe, Melissa

2009-01-01

361

abundance: High Redshift Cluster Abundance  

NASA Astrophysics Data System (ADS)

abundance, written in Fortran, provides driver and fitting routines to compute the predicted number of clusters in a ?CDM cosmology that agrees with CMB, SN, BAO, and H0 measurements (up to 2010) at some specified parameter confidence and the mass that would rule out that cosmology at some specified sample confidence. It also computes the expected number of such clusters in the light cone and the Eddington bias factor that must be applied to observed masses.

Mortonson, Michael; Hu, Wayne; Huterer, Dragan

2014-01-01

362

Side Chain and Backbone Dynamics of Phospholamban in Phospholipid Bilayers Utilizing 2H and 15N Solid-State NMR Spectroscopy†  

PubMed Central

2H and 15N solid-state NMR spectroscopic techniques were used to investigate both the side chain and backbone dynamics of wild-type phospholamban (WT-PLB) and its phosphorylated form (P-PLB) incorporated into 1-palmitoyl-2-oleoyl-sn-glycerophosphocholine (POPC) phospholipid bilayers. 2H NMR spectra of site-specific CD3-labeled WT-PLB (at Leu51, Ala24, and Ala15) in POPC bilayers were similar under frozen conditions (-25 °C). However, significant differences in the line shapes of the 2H NMR spectra were observed in the liquid crystalline phase at and above 0 °C. The 2H NMR spectra indicate that Leu51, located toward the lower end of the transmembrane (TM) helix, shows restricted side chain motion, implying that it is embedded inside the POPC lipid bilayer. Additionally, the line shape of the 2H NMR spectrum of CD3-Ala24 reveals more side chain dynamics, indicating that this residue (located in the upper end of the TM helix) has additional backbone and internal side chain motions. 2H NMR spectra of both WT-PLB and P-PLB with CD3-Ala15 exhibit strong isotropic spectral line shapes. The dynamic isotropic nature of the 2H peak can be attributed to side chain and backbone motions to residues located in an aqueous environment outside the membrane. Also, the spectra of 15N-labeled amide WT-PLB at Leu51 and Leu42 residues showed only a single powder pattern component indicating that these two 15N-labeled residues located in the TM helix are motionally restricted at 25 °C. Conversely, 15N-labeled amide WT-PLB at Ala11 located in the cytoplasmic domain showed both powder and isotropic components at 25 °C. Upon phosphorylation, the mobile component contribution increases at Ala11. The 2H and 15N NMR data indicate significant backbone motion for the cytoplasmic domain of WT-PLB when compared to the transmembrane section.

Abu-Baker, Shadi; Lu, Jun-Xia; Chu, Shidong; Brinn, Clarke C.; Makaroff, Christopher A.; Lorigan, Gary A.

2009-01-01

363

[Studies on the protein and amino-acid metabolism of laying hens using 15N-labelled casein. 15N-incorporation into N-fractions and amino acids of various parts of the body].  

PubMed

Four colostomized Leghorn hens were fed, during 6 days, 15N-labelled casein as sole protein source. Two animals were slaughtered 48 hours, the other two 144 hours after the last 15N-application. The share of TCE-soluble N in total N averaged 16% for the body parts analysed, i.e. meat, bone, liver, kidneys, oviducts, residual viscera and other. The variation of the lysine, histidine and arginine levels in the body parts ranged from 3.6 to 7.9 g, 1.1. to 3.7 g and 6.4 to 7.4 g in 16.7 g hydrolysate N, respectively. Except for feathers, the analysed body parts contained and excess amount of heavy nitrogen. The degree of labelling was found to depend on the time of slaughtering after the tracer application. In the liver and in the oviduct being metabolically active organs, the 15N-excess in the total N fraction decreased by 45% between the 2nd and the 6th days after 15N-feeding, whilst in the meat it went down by 20%. The decline of the 15N-concentration in the TCE-soluble N compounds was faster than in the total N-fraction. Out of the body samples analysed, the lysine of the liver having 0.26 atom % 15N-excess was found to be more strongly labelled in hens 1 and 2. The amino acid arginine reached about the same level of labelling, the 15N-frequency of histidine being the lowest. PMID:603400

Richter, G

1977-12-01

364

Chain packing in glassy polymers by natural-abundance 13C-13C spin diffusion using 2D centerband-only detection of exchange.  

PubMed

The proximities of specific subgroups of nearest-neighbor chains in glassy polymers are revealed by distance-dependent (13)C-(13)C dipolar couplings and spin diffusion. The measurement of such proximities is practical even with natural-abundance levels of (13)C using a 2D version of centerband-only detection of exchange (CODEX). Two-dimensional CODEX is a relaxation-compensated experiment that avoids the problems associated with variations in T(1)(C)'s due to dynamic site heterogeneity in the glass. Isotropic chemical shifts are encoded in the t(1) preparation times before and after mixing, and variations in T(2)'s are compensated by an S(0) reference (no mixing). Data acquisition involves acquisition of an S(0) reference signal on alternate scans, and the active control of power amplifiers, to achieve stability and accuracy over long accumulation times. The model system to calibrate spin diffusion is the polymer itself. For a mixing time of 200 ms, only (13)C-(13)C pairs separated by one or two bonds (2.5 Å) show cross peaks, which therefore identify reference intrachain proximities. For a mixing time of 1200 ms, 5 Å interchain proximities appear. The resulting cross peaks are used in a simple and direct way to compare nonrandom chain packing for two commercial polycarbonates with decidedly different mechanical properties. PMID:21306158

Singh, Manmilan; Schaefer, Jacob

2011-03-01

365

The use of natural abundance carbon-13 to identify and quantify sources of emitted carbon dioxide in a calcareous southern Ontario Luvisolic soil  

NASA Astrophysics Data System (ADS)

Three studies Were conducted at the Elora Research Station (ERS) on a Luvisolic soil to investigate the soil inorganic carbon (SIC) and soil organic carbon (SOC) components contributing to the CO2 flux (FC) using natural 13C abundance. SIC contributed to the FC in intact soil incubations. Soil disruption exacerbated the release of CO2 from both pedogenic and lithogenic carbonates. Field and laboratory techniques to obtain the delta13C of respired CO2 (delta13CR) were compared. Short-term deployment of non flow-through non steady-state chambers and the use of the simple two-ended mass balance approach to derive delta 13CR were found acceptable to apply to the ERS site. The delta13CR from a corn field at ERS with a history of multiple C4 and C3 crop rotations was partitioned into SIC and SOC components using two approaches. Root respiration contributed 2% - 64% and carbonates contribute up to 20% to the FC.

Wilton, Meaghan

366

Purification, recovery, and laser-driven fluorination of silicon from dissolved and particulate silica for the measurement of natural stable isotope abundances.  

PubMed

A procedure for the purification, recovery, and determination of isotopic abundances of silicon from biogenic and lithogenic particulate matter and dissolved silicic acid is reported. Purification involves the reaction of acid molybdate with dissolved silicon in natural waters or that produced by the dissolution of particulate silica by hydrofluoric acid. The resulting silicomolybdic acid is then quantitatively precipitated by reaction with triethylamine hydrochloride. The silicon is recovered as silicon dioxide through stepwise combustion of the dried precipitate. Fluorination of the product for isotopic analysis is accomplished by laser heating under pure fluorine generated by the decomposition of a fluorine-based salt. The resulting silicon tetrafluoride is separated from hydrogen fluoride and other fluorination byproducts cryogenically using a variable-temperature cold trap. Yields for silicon recovery are 99.9% for precipitation and greater than 95% for the purification/fluorination procedure. Reproducibility of the isotopic composition for pure quartz granules processed through the procedure is ±0.1‰ for ?(30)Si. PMID:21619245

De La Rocha, C L; Brzezinski, M A; Deniro, M J

1996-11-01

367

The physical state of osmoregulatory solutes in unicellular algae. A natural-abundance carbon-13 nuclear-magnetic-resonance relaxation study.  

PubMed Central

Natural-abundance 13C n.m.r. spin-lattice relaxation-time measurements have been carried out on intact cells of the unicellular blue--green alga Synechococcus sp. and the unicellular green alga Dunaliella salina, with the aim of characterizing the environments of the organic osmoregulatory solutes in these salt-tolerant organisms. In Synechococcus sp., all of the major organic osmoregulatory solute, 2-O-alpha-D-glucopyranosylglycerol, is visible in spectra of intact cells. Its rotational motion in the cell is slower by a factor of approx. 2.4 than in aqueous solution, but the molecule is still freely mobile and therefore able to contribute to the osmotic balance. In D. salina, only about 60% of the osmoregulatory solute glycerol is visible in spectra of intact cells. The rotational mobility of this observable fraction is approximately half that found in aqueous solution, but the data also indicate that there is a significant concentration of some paramagnetic species in D. salina which contributes to the overall spin-lattice relaxation of the glycerol carbon atoms. The non-observable fraction, which must correspond to glycerol molecules that have very broad 13C resonances and that are in slow exchange with bulk glycerol, has not been properly characterized as yet, but may represent glycerol in the chloroplast. The implications of these findings in relation to the physical state of the cytoplasm and the mechanism of osmoregulation in these cells are discussed.

Norton, R S; MacKay, M A; Borowitzka, L J

1982-01-01

368

A novel method for measuring long range proton-proton J coupling constants in multi-methylene fragments with 13C in natural abundance  

NASA Astrophysics Data System (ADS)

A new heteronuclear two-dimensional NMR experiment, X.E.COSY, is described which makes possible the measurement of 3JHH coupling constants between adjacent methylene groups in multi-methylene fragments. This new experiment exploits E.COSY multiplet structures based on large heteronuclear one-bond 1JXH coupling constants for resolving basic patterns. It necessitates only one NMR-active heteronuclear spin per molecule, and therefore is feasible with isotopes in natural abundance. X.E.COSY complements the XLOC pulse sequence, which works well for CH and CH3 groups but for methylene moieties only allows measurement of the sum of JHH coupling constants between a proton and the two protons attached to the heteronuclear spin. The new sequence has been tested on CH2CH and CH2CH2 moieties of a Gramicidin S sample, a C2 symmetric cyclic pentapeptide dimer. X.E.COSY will be useful for studying sidechain conformations in peptides and conformationally constrained peptides and peptide analogues containing methylene linkers or bridgers.

Briand, Jacques

1998-12-01

369

Biosynthetic control of the natural abundance of carbon 13 at specific positions within fatty acids in Escherichia coli. Evidence regarding the coupling of fatty acid and phospholipid synthesis  

SciTech Connect

Stable carbon isotope ratios (/sup 13/C//sup 12/C) at natural abundance levels have been determined for individual carbon atoms in each of the major phospholipid fatty acids of Escherichia coli grown on glucose as the sole carbon source. Two models were constructed for the isotope effects and carbon flow pathways which must be responsible for the observed isotopic fractionations. Both models incorporate a branch in the carbon flow at which fatty acyl-acyl carrier protein (acyl-ACP) is utilized either for complex lipid synthesis or for elongation by fatty acid synthetase. Depletion of carbon 13 in the carboxyl groups of myristic and palmitoleic acids (relative to carbonyl groups in precursor acyl-ACP's) was observed to occur at this branching site. Only one of the models was consistent both with this observation and with the observation that exogenous fatty acids are incorporated into phospholipids but are not elongated. The successful model has free fatty acid as the intermediate product coupling fatty acid biosynthesis to phospholipid synthesis. Essential to this pathway are those reactions catalyzed by thioesterases I and II as well as acyl-ACP synthetase, enzymes whose roles have previously been unknown in vivo.

Monson, K.D.; Hayes, J.M.

1980-12-10