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1

The role of calreticulin transacetylase in the activation of human platelet nitrite reductase by polyphenolic acetates.  

PubMed

Our earlier investigations demonstrated the remarkable activation of cytochrome P-450 reductase and nitric oxide synthase by 7,8-diacetoxy-4-methylcoumarin, a model polyphenolic acetate by way of acetylation, catalyzed by the Calreticulin. Protein acetyltransferase action of Calreticulin was hence termed Calreticulin transacetylase (CRTAase). Nitric oxide synthase and nitrite reductase are now considered as parts of nitric oxide cycle. The activation of platelets nitric oxide synthase by 7,8-diacetoxy-4-methylcoumarin has already been demonstrated by us. Also, there are reports that certain proteins such as cytochrome P-450 reductase and cytochrome P-450 are endowed with the nitrite reductase activity in mammalian cells. Keeping these facts in view, we turned our attention to probe whether 7,8-diacetoxy-4-methylcoumarin could alter the levels of nitric oxide independent of the action of nitric oxide synthase in the human platelets model. The incubation of 7,8-diacetoxy-4-methylcoumarin and nitrite with platelets caused significant elevation of nitric oxide and cyclic guanosine monophosphate levels possibly due to the activation of nitrite reductase. Several polyphenolic acetates were similarly found to activate the nitrite reductase in tune with their affinities as substrate to CRTAase. N-omega-Nitro-L-arginine methyl ester, the inhibitor of nitric oxide synthase, failed to reverse such an effect of 7,8-diacetoxy-4-methylcoumarin. Clotrimazole which is known to be an inhibitor of nitrite reductase, effectively abolished the 7,8-diacetoxy-4-methylcoumarin mediated enhancement of nitric oxide levels in platelets as well as the nitric oxide mediated effects; such as cyclic guanosine monophosphate levels as well as adenosine diphospate induced platelets aggregation due to nitrite. PMID:19182369

Arora, Shvetambri; Tyagi, Yogesh Kumar; Kumar, Ajit; Majumder, Syamantak; Saluja, Daman; Raj, Hanumantharao Guru; Chatterjee, Suvro; Saso, Luciano; Prasad, Ashok Kumar; Parmar, Virinder Singh

2009-02-01

2

7, 8-diacetoxy-4-methylcoumarin induced cell death in human tumor cells is influenced by calreticulin  

Microsoft Academic Search

Calreticulin (CRT), an endoplasmic reticulum resident protein demonstrates transacetylase activity in presence of 7, 8 diacetoxy-4-methyl coumarin (DAMC) in vitro. To investigate the possible role of CRT and DAMC mediated protein acetylation in cells, we investigated the effects of DAMC in tumor cells with different levels of CRT. DAMC was more toxic (clonogenicity, metabolic viability and proliferation) to human glioma

Amit Verma; Anant Narayan Bhatt; Abdullah Farooque; Suchit Khanna; Divya Khaitan; Mohan B. Arya; Anu Arya; Ashish Dhawan; Hanumantharao G. Raj; Daman Saluja; Ashok K. Prasad; Virinder S. Parmar; Bilikere S. Dwarakanath

2011-01-01

3

?-Lactone natural products and derivatives inactivate homoserine transacetylase, a target for antimicrobial agents  

Microsoft Academic Search

Homoserine transacetylase (HTA) catalyzes the transfer of an acetyl group from acetyl-CoA to the hydroxyl group of homoserine. This is the first committed step in the biosynthesis of methionine (Met) from aspartic acid in many fungi, Gram-positive and some Gram-negative bacteria. The enzyme is absent in higher eukaryotes and is important for microorganism growth in Met-poor environments, such as blood

Gianfranco De Pascale; Ishac Nazi; Paul H M Harrison; Gerard D Wright

2011-01-01

4

Calreticulin in the heart  

Microsoft Academic Search

Calreticulin is a Ca2+ binding\\/storage chaperone resident protein of the endoplasmic reticulum. This protein plays a key role in the calreticulin\\/calnexin cycle and the quality control pathways in the endoplasmic reticulum. Calreticulin deficiency is lethal due to impaired cardiac development. However, over-expression of the protein in developing and postnatal heart leads to bradycardia, complete heart block and sudden death. Ultrastructural

Marek Michalak; Lei Guo; Murray Robertson; Mira Lozak; Michal Opas

2004-01-01

5

Calreticulin and cancer.  

PubMed

Calreticulin (CRT) as a multi-functional endoplasmic reticulum protein is involved in a spectrum of cellular processes which ranges from calcium homeostasis and chaperoning to cell adhesion and finally malignant formation and progression. Previous studies have shown a contributing role for CRT in a range of different cancers. This present review will focus on the possible roles of CRT in the progression of malignant proliferation and the mechanisms involved in its contribution to cancer invasion. PMID:23392843

Zamanian, Mohammadreza; Veerakumarasivam, Abhi; Abdullah, Syahril; Rosli, Rozita

2013-04-01

6

Calreticulin’s Role(s) in Autoimmune Disorders  

Microsoft Academic Search

\\u000a For over ten years autoantibodies (Aab) against calreticulin (CRT) have been reported in a number of autoimmune disorders\\u000a including rheumatoid arthritis, Sjögren’s syndrome, celiac disease and complete congenital heart block. The most studied group\\u000a is patients with systemic lupus erythematosus (SLE), where Aab against CRT have been detected in 40% of all patients. A number\\u000a of studies have sought to

Richard D. Sontheimer; Doina Racila; Emil Racila; Paul Eggleton; Suzanne Donnelly

7

Calreticulin Mutations in Myeloproliferative Neoplasms  

PubMed Central

With the discovery of the JAK2V617F mutation in patients with Philadelphia chromosome-negative (Ph?) myeloproliferative neoplasms (MPNs) in 2005, major advances have been made in the diagnosis of MPNs, in understanding of their pathogenesis involving the JAK/STAT pathway, and finally in the development of novel therapies targeting this pathway. Nevertheless, it remains unknown which mutations exist in approximately one-third of patients with non-mutated JAK2 or MPL essential thrombocythemia (ET) and primary myelofibrosis (PMF). At the end of 2013, two studies identified recurrent mutations in the gene encoding calreticulin (CALR) using whole-exome sequencing. These mutations were revealed in the majority of ET and PMF patients with non-mutated JAK2 or MPL but not in polycythemia vera patients. Somatic 52-bp deletions (type 1 mutations) and recurrent 5-bp insertions (type 2 mutations) in exon 9 of the CALR gene (the last exon encoding the C-terminal amino acids of the protein calreticulin) were detected and found always to generate frameshift mutations. All detected mutant calreticulin proteins shared a novel amino acid sequence at the C-terminal. Mutations in CALR are acquired early in the clonal history of the disease, and they cause activation of JAK/STAT signaling. The CALR mutations are the second most frequent mutations in Ph? MPN patients after the JAK2V617F mutation, and their detection has significantly improved the diagnostic approach for ET and PMF. The characteristics of the CALR mutations as well as their diagnostic, clinical, and pathogenesis implications are discussed in this review. PMID:25386351

Lavi, Noa

2014-01-01

8

Calreticulin mutations in myeloproliferative neoplasms.  

PubMed

With the discovery of the JAK2V617F mutation in patients with Philadelphia chromosome-negative (Ph(-)) myeloproliferative neoplasms (MPNs) in 2005, major advances have been made in the diagnosis of MPNs, in understanding of their pathogenesis involving the JAK/STAT pathway, and finally in the development of novel therapies targeting this pathway. Nevertheless, it remains unknown which mutations exist in approximately one-third of patients with non-mutated JAK2 or MPL essential thrombocythemia (ET) and primary myelofibrosis (PMF). At the end of 2013, two studies identified recurrent mutations in the gene encoding calreticulin (CALR) using whole-exome sequencing. These mutations were revealed in the majority of ET and PMF patients with non-mutated JAK2 or MPL but not in polycythemia vera patients. Somatic 52-bp deletions (type 1 mutations) and recurrent 5-bp insertions (type 2 mutations) in exon 9 of the CALR gene (the last exon encoding the C-terminal amino acids of the protein calreticulin) were detected and found always to generate frameshift mutations. All detected mutant calreticulin proteins shared a novel amino acid sequence at the C-terminal. Mutations in CALR are acquired early in the clonal history of the disease, and they cause activation of JAK/STAT signaling. The CALR mutations are the second most frequent mutations in Ph(-) MPN patients after the JAK2V617F mutation, and their detection has significantly improved the diagnostic approach for ET and PMF. The characteristics of the CALR mutations as well as their diagnostic, clinical, and pathogenesis implications are discussed in this review. PMID:25386351

Lavi, Noa

2014-10-01

9

Calreticulin: one protein, one gene, many functions.  

PubMed Central

The endoplasmic reticulum (ER) plays a critical role in the synthesis and chaperoning of membrane-associated and secreted proteins. The membrane is also an important site of Ca(2+) storage and release. Calreticulin is a unique ER luminal resident protein. The protein affects many cellular functions, both in the ER lumen and outside of the ER environment. In the ER lumen, calreticulin performs two major functions: chaperoning and regulation of Ca(2+) homoeostasis. Calreticulin is a highly versatile lectin-like chaperone, and it participates during the synthesis of a variety of molecules, including ion channels, surface receptors, integrins and transporters. The protein also affects intracellular Ca(2+) homoeostasis by modulation of ER Ca(2+) storage and transport. Studies on the cell biology of calreticulin revealed that the ER membrane is a very dynamic intracellular compartment affecting many aspects of cell physiology. PMID:10567207

Michalak, M; Corbett, E F; Mesaeli, N; Nakamura, K; Opas, M

1999-01-01

10

Biochemical and Molecular Properties of Calreticulin  

Microsoft Academic Search

\\u000a Calreticulin is a highly abundant Ca2+-storage protein found in all cells of higher organisms, with the exception of erythrocytes. It is predominantly located in\\u000a the endoplasmic reticulum where, in tandem with the homologue calnexin, it performs an important role in glycoprotein folding,\\u000a such as in the assembly of MHC Class I complexes. Under conditions of cellular stress, calreticulin may be

Steven J. Johnson; Kjell O. Håkansson

11

Calreticulin, Cardiac Development and Congenital Complete Heart Block in Children  

Microsoft Academic Search

\\u000a Calreticulin is a Ca2+ binding chaperone resident in the lumen of endoplasmic reticulum. The protein is highly expressed in developing heart and\\u000a down-regulated after birth. In mice, calreticulin deficiency is lethal due to impaired cardiac development. Over-expression\\u000a of calreticulin in developing and postnatal heart leads to bradycardia, complete heart block and sudden death. This indicates\\u000a that calreticulin plays an important

Barbara Knoblach; Kimitoshi Nakamura; Murray Robertson; Marek Michalak

12

Calreticulin: not just another calcium-binding protein  

Microsoft Academic Search

In this paper we review some of the rapidly expanding information about calreticulin, a Ca(2+)-binding\\/storage protein of the endoplasmic reticulum. The emphasis is placed on the structure and function of calreticulin. We believe that calreticulin is a multifunctional Ca(2+)-binding protein and that distinct functional properties of the protein may be localized to each of the three structural domains of calreticulin.

P. D. Nash; Michal Opas; Marek Michalak

1994-01-01

13

Calreticulin modulates cell adhesiveness via regulation of vinculin expression  

Microsoft Academic Search

Calreticulin is an ubiquitous and highly con- served high capacity Ca2+-binding protein that plays a major role in Ca 2÷ storage within the lumen of the ER. Here, using L fibroblast cell lines expressing different levels of calreticulin, we show that calreticulin plays a role in the control of cell adhesiveness via regulation of expression of vinculin, a cytoskeletal protein

Michal Opas; Greta K. Jass; Nasrin Mesaeli; Marek Michalak

1996-01-01

14

Identification and localization of calreticulin in plant cells  

Microsoft Academic Search

Summary In the present study we have investigated the presence and distribution of calreticulin in plant protoplasts. Calreticulin was purified from plant homogenates using a selective ammonium sulfate precipitation procedure developed for the purification of mammalian calreticulins and shown to bind calcium in45Ca2+ overlay assays. The protein was localized to plant cell endoplasmic reticulum by the indirect immunofluorescence staining of

M. Opas; S. Tharin; R. E. Milner; M. Michalak

1996-01-01

15

Clinicopathological significance of calreticulin in breast invasive ductal carcinoma  

Microsoft Academic Search

Calreticulin is a chaperone protein located in the lumen of the endoplasmic reticulum. The association of calreticulin with pathological conditions such as autoimmune disorders and certain types of cancer have been reported. However, little is known about its role in the pathogenesis of breast cancer. The aim of this study was to determine the expression of calreticulin in vitro and

Zin-Mar Lwin; Chunhua Guo; Agus Salim; George Wai-Cheong Yip; Fook-Tim Chew; Jiang Nan; Aye Aye Thike; Puay-Hoon Tan; Boon-Huat Bay

2010-01-01

16

Calreticulin-melatonin. An unexpected relationship.  

PubMed

Increasing evidence suggests that melatonin can exert some effect at nuclear level. Previous experiments using binding techniques clearly showed the existence of specific melatonin binding sites in cell nucleus of rat liver. To further identify these sites, nuclear extracts from rat hepatocytes were treated with different percentages of ammonium sulfate and purified by affinity chromatography. Subsequent ligand blot analysis shows the presence of two polypeptides of approximately 60 and approximately 74 kDa that bind specifically to melatonin. N-Terminal sequence analysis showed that the 60 kDa protein shares a high homology with rat calreticulin, whereas the 74 kDa protein shows no homology with any known protein. The binding of melatonin to calreticulin was further characterized incubating 2-[125I]melatonin with recombinant calreticulin. Binding kinetics show a Kd = 1.08 +/- 0.2 nm and Bmax = 290 +/- 34 fmol.mg protein-1, compatible with other binding sites of melatonin in the cell. The presence of calreticulin was further identified by Western blot analysis, and the lack of endoplasmic reticulum contamination in our material was assessed by Western blot and immunostaining with anti-calnexin Ig. The results suggest that calreticulin may represent a new class of high-affinity melatonin binding sites involved in some functions of the indoleamine including genomic regulation. PMID:12603316

Macías, Manuel; Escames, Germaine; Leon, Josefa; Coto, Ana; Sbihi, Younes; Osuna, Antonio; Acuña-Castroviejo, Darío

2003-03-01

17

Calreticulin in the immune system: ins and outs.  

PubMed

Calreticulin is a calcium-binding chaperone that has several functions in the immune response. In the endoplasmic reticulum (ER), calreticulin facilitates the folding of major histocompatibility complex (MHC) class I molecules and their assembly factor tapasin, thereby influencing antigen presentation to cytotoxic T cells. Although calreticulin is normally ER-resident, it is found at the cell surface of living cancer cells and dying cells. Here, calreticulin promotes cellular phagocytic uptake. In tumor vaccine models, drugs that induce cell surface calreticulin confer enhanced tumor protection in an extracellular calreticulin-dependent manner. Much remains to be understood about the roles of calreticulin in these distinct functions. Further investigations are important towards advancing basic knowledge of glycoprotein-folding pathways, and towards developing new cancer therapeutic strategies. PMID:22959412

Raghavan, Malini; Wijeyesakere, Sanjeeva J; Peters, Larry Robert; Del Cid, Natasha

2013-01-01

18

Implications of Calreticulin Function in Parasite Biology  

Microsoft Academic Search

Calreticulin (CR) is a Ca2+-binding, multifunctional protein. The amazing array of CR-associated functions range from intracellular activities in secondary messenger release, protein folding and the modulation of gene expression to potential interactions with host receptors and signaling machinery and recognition by the host immune system. The multifunctional nature of CR may impact upon the ability of cells to recognize extracellular

H. L. Nakhasi; G. P. Pogue; R. C. Duncan; M. Joshi; C. D. Atreya; N. S. Lee; D. M. Dwyer

1998-01-01

19

Calreticulin, a Ca 2+-binding chaperone of the endoplasmic reticulum  

Microsoft Academic Search

Calreticulin is a 46-kDa Ca2+-binding chaperone found across a diverse range of species. The protein is involved in the regulation of intracellular Ca2+ homeostasis and endoplasmic reticulum (ER) Ca2+ storage capacity. Calreticulin is also an important molecular chaperone involved in “quality control” within secretory pathways. The protein contains structurally and functionally unique domains with specialized functions. Studies on calreticulin knockout

Pascal Gelebart; Michal Opas; Marek Michalak

2005-01-01

20

Calreticulin: Roles in Cell-Surface Protein Expression  

PubMed Central

In order to perform their designated functions, proteins require precise subcellular localizations. For cell-surface proteins, such as receptors and channels, they are able to transduce signals only when properly targeted to the cell membrane. Calreticulin is a multi-functional chaperone protein involved in protein folding, maturation, and trafficking. However, evidence has been accumulating that calreticulin can also negatively regulate the surface expression of certain receptors and channels. In these instances, depletion of calreticulin enhances cell-surface expression and function. In this review, we discuss the role of calreticulin with a focus on its negative effects on the expression of cell-surface proteins. PMID:25230046

Jiang, Yue; Dey, Sandeepa; Matsunami, Hiroaki

2014-01-01

21

Calreticulin recognizes misfolded HLA-A2 heavy chains  

PubMed Central

Our studies investigated functional interactions between calreticulin, an endoplasmic reticulum chaperone, and major histocompatibility complex (MHC) class I molecules. Using in vitro thermal aggregation assays, we established that calreticulin can inhibit heat-induced aggregation of soluble, peptide-deficient HLA-A2 purified from supernatants of insect cells. The presence of HLA-A2-specific peptides also inhibits heat-induced aggregation. Inhibition of heat-induced aggregation of peptide-deficient HLA-A2 by calreticulin correlates with a rescue of the HLA-A2 heavy chain from precipitation, by forming high-molecular-weight complexes with calreticulin. Complex formation between HLA-A2 heavy chains and calreticulin occurs at 50°C but not 37°C, suggesting polypeptide-based interactions between the HLA-A2 heavy chain and calreticulin. Once complexes are formed, the addition of peptide is not sufficient to trigger efficient assembly of heavy chain/?2m/peptide complexes. Using a fluorescent peptide-based binding assay, we show that calreticulin does not enhance peptide binding by HLA-A2 at 37°C. We also show that calreticulin itself is converted to oligomeric species on exposure to 37°C or higher temperatures, and that oligomeric forms of calreticulin are active in inhibiting thermal aggregation of peptide-deficient HLA-A2. Taken together, these results suggest that calreticulin functions in the recognition of misfolded MHC class I heavy chains in the endoplasmic reticulum. However, in the absence of other endoplasmic reticulum components, calreticulin by itself does not enhance the assembly of misfolded MHC class I heavy chains with ?2m and peptides. PMID:11983893

Mancino, Laura; Rizvi, Syed Monem; Lapinski, Philip Edward; Raghavan, Malini

2002-01-01

22

Distinct clinical characteristics of myeloproliferative neoplasms with calreticulin mutations  

PubMed Central

Somatic insertions/deletions in the calreticulin gene have recently been discovered to be causative alterations in myeloproliferative neoplasms. A combination of qualitative and quantitative allele-specific polymerase chain reaction, fragment-sizing, high resolution melting and Sanger-sequencing was applied for the detection of three driver mutations (in Janus kinase 2, calreticulin and myeloproliferative leukemia virus oncogene genes) in 289 cases of essential thrombocythemia and 99 cases of primary myelofibrosis. In essential thrombocythemia, 154 (53%) Janus kinase 2 V617F, 96 (33%) calreticulin, 9 (3%) myeloproliferative leukemia virus oncogene gene mutation-positive and 30 triple-negative (11%) cases were identified, while in primary myelofibrosis 56 (57%) Janus kinase 2 V617F, 25 (25%) calreticulin, 7 (7%) myeloproliferative leukemia virus oncogene gene mutation-positive and 11 (11%) triple-negative cases were identified. Patients positive for the calreticulin mutation were younger and had higher platelet counts compared to Janus kinase 2 mutation-positive counterparts. Calreticulin mutation-positive patients with essential thrombocythemia showed a lower risk of developing venous thrombosis, but no difference in overall survival. Calreticulin mutation-positive patients with primary myelofibrosis had a better overall survival compared to that of the Janus kinase 2 mutation-positive (P=0.04) or triple-negative cases (P=0.01). Type 2 calreticulin mutation occurred more frequently in essential thrombocythemia than in primary myelofibrosis (P=0.049). In essential thrombocythemia, the calreticulin mutational load was higher than the Janus kinase 2 mutational load (P<0.001), and increased gradually in advanced stages. Calreticulin mutational load influenced blood counts even at the time point of diagnosis in essential thrombocythemia. We confirm that calreticulin mutation is associated with distinct clinical characteristics and explored relationships between mutation type, load and clinical outcome. PMID:24895336

Andrikovics, Hajnalka; Krahling, Tunde; Balassa, Katalin; Halm, Gabriella; Bors, Andras; Koszarska, Magdalena; Batai, Arpad; Dolgos, Janos; Csomor, Judit; Egyed, Miklos; Sipos, Andrea; Remenyi, Peter; Tordai, Attila; Masszi, Tamas

2014-01-01

23

Distinct clinical characteristics of myeloproliferative neoplasms with calreticulin mutations.  

PubMed

Somatic insertions/deletions in the calreticulin gene have recently been discovered to be causative alterations in myeloproliferative neoplasms. A combination of qualitative and quantitative allele-specific polymerase chain reaction, fragment-sizing, high resolution melting and Sanger-sequencing was applied for the detection of three driver mutations (in Janus kinase 2, calreticulin and myeloproliferative leukemia virus oncogene genes) in 289 cases of essential thrombocythemia and 99 cases of primary myelofibrosis. In essential thrombocythemia, 154 (53%) Janus kinase 2 V617F, 96 (33%) calreticulin, 9 (3%) myeloproliferative leukemia virus oncogene gene mutation-positive and 30 triple-negative (11%) cases were identified, while in primary myelofibrosis 56 (57%) Janus kinase 2 V617F, 25 (25%) calreticulin, 7 (7%) myeloproliferative leukemia virus oncogene gene mutation-positive and 11 (11%) triple-negative cases were identified. Patients positive for the calreticulin mutation were younger and had higher platelet counts compared to Janus kinase 2 mutation-positive counterparts. Calreticulin mutation-positive patients with essential thrombocythemia showed a lower risk of developing venous thrombosis, but no difference in overall survival. Calreticulin mutation-positive patients with primary myelofibrosis had a better overall survival compared to that of the Janus kinase 2 mutation-positive (P=0.04) or triple-negative cases (P=0.01). Type 2 calreticulin mutation occurred more frequently in essential thrombocythemia than in primary myelofibrosis (P=0.049). In essential thrombocythemia, the calreticulin mutational load was higher than the Janus kinase 2 mutational load (P<0.001), and increased gradually in advanced stages. Calreticulin mutational load influenced blood counts even at the time point of diagnosis in essential thrombocythemia. We confirm that calreticulin mutation is associated with distinct clinical characteristics and explored relationships between mutation type, load and clinical outcome. PMID:24895336

Andrikovics, Hajnalka; Krahling, Tunde; Balassa, Katalin; Halm, Gabriella; Bors, Andras; Koszarska, Magdalena; Batai, Arpad; Dolgos, Janos; Csomor, Judit; Egyed, Miklos; Sipos, Andrea; Remenyi, Peter; Tordai, Attila; Masszi, Tamas

2014-07-01

24

Parasite calreticulin: possible roles in the parasite\\/host interface  

Microsoft Academic Search

Calreticulin, a calcium-binding protein of the endoplasmic reticulum, is a highly conserved multifunctional protein, pre - sent in every cell of higher organisms, except erythrocytes. The amazing array of calreticulin-associated important functions include lectin-like chaperoning, calcium storage and signa - ling, modulation of gene expression, cell adhesion, fagocyto - sis of apoptotic cells, autoimmunity, angiogenesis, tumoral g rowth, lytic activity

V. FERREIRA; C. VALCK; A. ROJAS; A. FERREIRA

25

Isolation and characterization of Leishmania donovani calreticulin gene and its conservation of the RNA binding activity  

Microsoft Academic Search

Calreticulin has been implicated in multiple cell functions. Recently, we have shown that both human and simian calreticulin are RNA binding proteins and that their binding activity is due to phosphorylation. To demonstrate that the RNA binding property of calreticulin is an intrinsic part of this multi-functional molecule and is evolutionarily conserved, we isolated and characterized the calreticulin gene from

Manju Joshi; Gregory P. Pogue; Robert C. Duncan; Nancy S. Lee; Nishi K. Singh; Chintamani D. Atreya; Dennis M. Dwyer; Hira L. Nakhasi

1996-01-01

26

Lipoyl content and other properties of the protein X and the transacetylase components of the pyruvate dehydrogenase complex  

SciTech Connect

Previous work demonstrated by structural and immunological techniques that protein X (X) was distinct from the transacetylase (E2) but that regions of X and E2 (specifically including the portions acetylated) were similar. Trypsin cleaved X and E2 into large domains giving acetylated portions with apparent M/sub r/ values of approx.20 kdal and approx.38 kdal, respectively. Purified (denatured) E2 and X subunits were prepared and amino acid compositions determined. Reduced subunits were reacted with FDNB and acid hydrolyzed. Bis(DNP)dihydrolipoic was extracted into ethylacetate and quantitated by HPLC (epsilon = 25 O.D.mM/sup -1/cm/sup -1/ at 340 nm) and the levels normalized based on the amino acid analysis of the acid hydrolysates. E2 and X were estimated to contain about 1 lipoyl moiety per subunit. Following dihydrolipoyl dehydrogenase-dependent NADH reduction of E2-X, 1.5-2 /sup 14/C-NEM per subunit were incorporated into E2 and X consistent with reduction of one lipoyl moiety per subunit. Incorporation into E2-X subcomplex of > 90 acetyl groups per molecule of subcomplex led to > 1.5 acetyl group incorporated per X and per E2 subunit and nearly eliminated NADH-dependent incorporation of /sup 14/C-NEM into these subunits suggesting diacetyl moieties were formed. Consistent with that possibility, acetylation to high levels yielded rapid and slowly exchanging acetyl groups on both E2 and X.

Radke, G.A.; Rahmatullah, M.; Jilka, J.M; Roche, T.E.

1986-05-01

27

Vasostatin, a Calreticulin Fragment, Inhibits Angiogenesis and Suppresses Tumor Growth  

Microsoft Academic Search

Summary An endothelial cell inhibitor was purified from supernatant of an Epstein-Barr virus-immortal- ized cell line and identified as fragments of calreticulin. The purified recombinant NH 2 -termi- nal domain of calreticulin (amino acids 1-180) inhibited the proliferation of endothelial cells, but not cells of other lineages, and suppressed angiogenesis in vivo. We have named this NH 2 - terminal

Sandra E. Pike; Lei Yao; Karen D. Jones; Barry Cherney; Ettore Appella; Kazuyasu Sakaguchi; Hira Nakhasi; Julie Teruya-Feldstein; Peter Wirth; Ghanshyam Gupta; Giovanna Tosato

2010-01-01

28

ERp57 Does Not Require Interactions with Calnexin and Calreticulin to Promote Assembly of Class I Histocompatibility Molecules, and It Enhances Peptide Loading Independently of Its Redox Activity*  

PubMed Central

ERp57 is a thiol oxidoreductase that catalyzes disulfide formation in heavy chains of class I histocompatibility molecules. It also forms a mixed disulfide with tapasin within the class I peptide loading complex, stabilizing the complex and promoting efficient binding of peptides to class I molecules. Since ERp57 associates with the lectin chaperones calnexin and calreticulin, it is thought that ERp57 requires these chaperones to gain access to its substrates. To test this idea, we examined class I biogenesis in cells lacking calnexin or calreticulin or that express an ERp57 mutant that fails to bind to these chaperones. Remarkably, heavy chain disulfides formed at the same rate in these cells as in wild type cells. Moreover, ERp57 formed a mixed disulfide with tapasin and promoted efficient peptide loading in the absence of interactions with calnexin and calreticulin. These findings suggest that ERp57 has the capacity to recognize its substrates directly in addition to being recruited through lectin chaperones. We also found that calreticulin could be recruited into the peptide loading complex in the absence of interactions with both ERp57 and substrate oligosaccharides, demonstrating the importance of its polypeptide binding site in substrate recognition. Finally, by inactivating the redox-active sites of ERp57, we demonstrate that its enzymatic activity is dispensable in stabilizing the peptide loading complex and in supporting efficient peptide loading. Thus, ERp57 appears to play a structural rather than catalytic role within the peptide loading complex. PMID:19196713

Zhang, Yinan; Kozlov, Guennadi; Pocanschi, Cosmin L.; Brockmeier, Ulf; Ireland, Breanna S.; Maattanen, Pekka; Howe, Chris; Elliott, Tim; Gehring, Kalle; Williams, David B.

2009-01-01

29

Overexpression of Calreticulin in Malignant and Benign Breast Tumors: Relationship with Humoral Immunity  

Microsoft Academic Search

Objective: Calreticulin is a multicompartmental protein which regulates many important cellular responses. The aim of this study was to elucidate whether the intensity and location of calreticulin overexpression in tumor cells are related to the elevated humoral immunity to calreticulin in patients with benign or malignant breast disease. Methods: This study involved 27 patients with benign and 58 patients with

Daniel Sánchez; Aneta Pekáriková; Marko Buta

2012-01-01

30

Antiangiogenic and Antitumor Effects of Trypanosoma cruzi Calreticulin  

Microsoft Academic Search

BackgroundIn Latin America, 18 million people are infected with Trypanosoma cruzi, the agent of Chagas' disease, with the greatest economic burden. Vertebrate calreticulins (CRT) are multifunctional, intra- and extracellular proteins. In the endoplasmic reticulum (ER) they bind calcium and act as chaperones. Since human CRT (HuCRT) is antiangiogenic and suppresses tumor growth, the presence of these functions in the parasite

Nandy C. López; Carolina Valck; Galia Ramírez; Margarita Rodríguez; Carolina Ribeiro; Juana Orellana; Ismael Maldonado; Adriana Albini; Daniel Anacona; David Lemus; Lorena Aguilar; Wilhelm Schwaeble; Arturo Ferreira

2010-01-01

31

Enhancement of vaccinia vaccine potency by linkage of tumor antigen gene to gene encoding calreticulin  

Microsoft Academic Search

Vaccinia vaccines have become important vectors for antigen-specific immunotherapy. Calreticulin has been shown to enhance MHC class I presentation of linked peptide\\/protein and may be useful for antigen-specific cancer treatment. An innovative vaccine administering antigen linked to calreticulin via a vaccinia vector may generate a potent antigen-specific antitumor response. We tested the efficacy of linking calreticulin (CRT) to model antigen

Chia-Jung Hsieh; Tae Woo Kim; Chien-Fu Hung; Jeremy Juang; Michelle Moniz; David A. K. Boyd; Liangmei He; Pei-Jer Chen; Chien-Hung Chen; T.-C. Wu

2004-01-01

32

Calreticulin expression in infiltrating ductal breast carcinomas: relationships with disease progression and humoral immune responses.  

PubMed

The aim of this study was to evaluate calreticulin expression in infiltrating ductal breast carcinomas (IDCAs), as well as its relationships with clinicopathological parameters of the disease. Using a two-dimensional gel electrophoresis/matrix-assisted laser desorption ionization time of flight mass spectrometry investigation coupled to an immunohistochemical approach, we have assessed the expression of calreticulin in IDCAs, as well as in other types of breast tumors. The humoral immune response against calreticulin was estimated using a serological proteomics-based strategy. Proteomic analyses revealed an increased expression of calreticulin in IDCA tumors. Using immunohistochemistry, overexpression of calreticulin was confirmed in 51 additional tumor specimens. Statistical analyses revealed, however, no significant correlations between calreticulin expression and clinicopathological parameters of the disease including tumor stage, patient age, SBR grade, and lymph node metastasis occurrence. A significant association was found, however, with estrogen receptor status. This study demonstrates the upregulation of calreticulin in IDCA tissues which may highlight its involvement in breast cancer development. Our findings also support a link between calreticulin expression and estrogen transduction pathways. Our results do not, however, support the involvement of calreticulin in the development of a humoral immune response in IDCAs. PMID:23334957

Kabbage, Maria; Trimeche, Mounir; Bergaoui, Sarra; Hammann, Philippe; Kuhn, Lauriane; Hamrita, Bechr; ben Nasr, Hela; Chaieb, Anouar; Chouchane, Lotfi; Chahed, Karim

2013-04-01

33

Nerve growth factor induces the expression of chaperone protein calreticulin in human epithelial ovarian cells.  

PubMed

Epithelial ovarian cancer is highly angiogenic and high expression of Nerve Growth Factor (NGF), a proangiogenic protein. Calreticulin is a multifunctional protein with anti-angiogenic properties and its translocation to the tumor cell membrane promotes recognition and engulfment by dendritic cells. The aim of this work was to evaluate calreticulin expression in human normal ovaries, benign and borderline tumors, and epithelial ovarian cancer samples and to evaluate whether NGF regulates calreticulin expression in human ovarian surface epithelium and in epithelial ovarian cancer cell lines. Calreticulin mRNA and protein levels were analyzed using RT-PCR, Western blot and immunohistochemistry in 67 human ovarian samples obtained from our Institution. Calreticulin expression induced by NGF stimulation in cell lines was evaluated using RT-PCR, Western blot and immunocytochemistry. We found a significant increase of calreticulin mRNA levels in epithelial ovarian cancer samples as compared to normal ovaries, benign tumors, and borderline tumors. Calreticulin protein levels, evaluated by Western blot, were also increased in epithelial ovarian cancer with respect to benign and borderline tumors. When HOSE and A2780 cell lines were stimulated with Nerve Growth Factor, we found an increase in calreticulin protein levels compared to controls. This effect was reverted by GW441756, a TRKA specific inhibitor. These results suggest that NGF regulates calreticulin protein levels in epithelial ovarian cells through TRKA receptor activation. PMID:22773372

Vera, C; Tapia, V; Kohan, K; Gabler, F; Ferreira, A; Selman, A; Vega, M; Romero, C

2012-07-01

34

Rubella virus glycoprotein interaction with the endoplasmicreticulum calreticulin and calnexin  

Microsoft Academic Search

Summary.  ?Very little is known about the cellular factors that are required for the maturation of rubella virus glycoproteins (E2 and\\u000a E1) in the endoplasmic reticulum of the infected cell. In the present study, we established the interaction of the ER chaperone\\u000a proteins, calreticulin and calnexin, with the RV E1 and E2 proteins in cells stably expressing the viral proteins. The

H. L. Nakhasi; M. Ramanujam; C. D. Atreya; T. C. Hobman; N. Lee; A. Esmaili; R. C. Duncan

2001-01-01

35

An in vivo role for Trypanosoma cruzi calreticulin in antiangiogenesis  

Microsoft Academic Search

Angiogenesis leads to neovascularization from existing blood vessels. It is associated with tumor growth and metastasis and is regulated by pro- and antiangiogenic molecules, some of them currently under clinical trials for cancer treatment. During the last few years we have cloned, sequenced and expressed a Trypanosoma cruzi calreticulin gene (TcCRT). Its product, TcCRT, a 45kDa protein, is more than

María C. Molina; Viviana Ferreira; Carolina Valck; Lorena Aguilar; Juana Orellana; Alvaro Rojas; Galia Ramirez; Rosario Billetta; Wilhelm Schwaeble; David Lemus; Arturo Ferreira

2005-01-01

36

Calreticulin in human pregnancy and pre-eclampsia  

Microsoft Academic Search

Pre-eclampsia is a disorder of human pregnancy that involves pregnancy-induced maternal hypertension and proteinuria. Evidence indicates that pre-eclampsia involves widespread activation of maternal endothelial cells. Calreticulin is a ubiquitously expressed, multi-functional protein that has been shown to have both pro- and anti-inflammatory effects on cultured endothelial cells in vitro and in whole animals. In order to clarify the role of

V. Y. Gu; M. H. Wong; J. L. Stevenson; K. E. Crawford; S. P. Brennecke; N. M. Gude

2008-01-01

37

Calreticulin displays in vivo peptide-binding activity and can elicit CTL responses against bound peptides.  

PubMed

Calreticulin is an endoplasmic reticulum (ER) chaperone that displays lectin activity and contributes to the folding pathways for nascent glycoproteins. Calreticulin also participates in the reactions yielding assembly of peptides onto nascent MHC class I molecules. By chemical and immunological criteria, we identify calreticulin as a peptide-binding protein and provide data indicating that calreticulin can elicit CTL responses to components of its bound peptide pool. In an adoptive immunotherapy protocol, dendritic cells pulsed with calreticulin isolated from B16/F10.9 murine melanoma, E.G7-OVA, or EL4 thymoma tumors elicited a CTL response to as yet unknown tumor-derived Ags or the known OVA Ag. To evaluate the relative efficacy of calreticulin in eliciting CTL responses, the ER chaperones GRP94/gp96, BiP, ERp72, and protein disulfide isomerase were purified in parallel from B16/F10.9, EL4, and E.G7-OVA tumors, and the capacity of the proteins to elicit CTL responses was compared. In both the B16/F10.9 and E.G7-OVA models, calreticulin was as effective as or more effective than GRP94/gp96 in eliciting CTL responses. Little to no activity was observed for BiP, ERp72, and protein disulfide isomerase. The observed antigenic activity of calreticulin was recapitulated in in vitro experiments, in which it was observed that pulsing of bone marrow dendritic cells with E.G7-OVA-derived calreticulin elicited sensitivity to lysis by OVA-specific CD8+ T cells. These data identify calreticulin as a peptide-binding protein and indicate that calreticulin-bound peptides can be re-presented on dendritic cell class I molecules for recognition by CD8+ T cells. PMID:10352256

Nair, S; Wearsch, P A; Mitchell, D A; Wassenberg, J J; Gilboa, E; Nicchitta, C V

1999-06-01

38

Modes of calreticulin recruitment to the major histocompatibility complex class I assembly pathway.  

PubMed

Major histocompatibility complex (MHC) class I molecules are ligands for T-cell receptors of CD8(+) T cells and inhibitory receptors of natural killer cells. Assembly of the heavy chain, light chain, and peptide components of MHC class I molecules occurs in the endoplasmic reticulum (ER). Specific assembly factors and generic ER chaperones, collectively called the MHC class I peptide loading complex (PLC), are required for MHC class I assembly. Calreticulin has an important role within the PLC and induces MHC class I cell surface expression, but the interactions and mechanisms involved are incompletely understood. We show that interactions with the thiol oxidoreductase ERp57 and substrate glycans are important for the recruitment of calreticulin into the PLC and for its functional activities in MHC class I assembly. The glycan and ERp57 binding sites of calreticulin contribute directly or indirectly to complexes between calreticulin and the MHC class I assembly factor tapasin and are important for maintaining steady-state levels of both tapasin and MHC class I heavy chains. A number of destabilizing conditions and mutations induce generic polypeptide binding sites on calreticulin and contribute to calreticulin-mediated suppression of misfolded protein aggregation in vitro. We show that generic polypeptide binding sites per se are insufficient for stable recruitment of calreticulin to PLC substrates in cells. However, such binding sites could contribute to substrate stabilization in a step that follows the glycan and ERp57-dependent recruitment of calreticulin to the PLC. PMID:19959473

Del Cid, Natasha; Jeffery, Elise; Rizvi, Syed Monem; Stamper, Ericca; Peters, Larry Robert; Brown, William Clay; Provoda, Chester; Raghavan, Malini

2010-02-12

39

NMR structure of the calreticulin P-domain Lars Ellgaard*, Roland Riek  

E-print Network

studies of the abundant endoplasmic reticulum chaperone calreticulin. The two homologous calcium-binding proteins calnexin (CNX) and calreticulin (CRT) serve as molecular chaper- ones in the endoplasmic reticulum (ER) of eukaryotic cells. They transiently bind to the majority of nascent and newly synthesized

Riek, Roland

40

Calreticulin Is a Negative Regulator of Bronchial Smooth Muscle Cell Proliferation  

PubMed Central

Background. Calreticulin controls the C/EBP?p42/p30 at the translational level trough a cis-regulatory CNG rich loop in the CEBPA mRNA. We determined the effects of steroids and long-acting beta-agonists on the p42/p30 ratio and on calreticulin expression in primary human bronchial smooth muscle (BSM) cells. Methods. The effects of budesonide (10?8?M) and formoterol (10?8?M) were studied in BSM cells pre-treated with siRNA targeting calreticulin. The expression of C/EBP? and calreticulin was determined by immuno-blotting. Automated cell counts were performed to measure proliferation. Results. All tested BSM cell lines (n = 5) expressed C/EBP? and calreticulin. In the presence of 5% FBS, the p42/p30 ratio significantly decreased (n = 3, P < 0.05) and coincided with BSM cell proliferation. High levels of calreticulin were associated with a decreased p42/p30 isoform ratio. FBS induced the expression of calreticulin (n = 3, P < 0.05), which was further increased by formoterol. siRNA targeting calreticulin increased the p42/p30 ratio in non-stimulated BSM cells and significantly inhibited the proliferation of PDGF-BB-stimulated BSM cells (n = 5, P < 0.05). Neither budesonide nor formoterol restored the p42 isoform expression. Conclusions. Our data show calreticulin is a negative regulator of C/EBP? protein expression in BSM cells. Modulation of calreticulin levels may provide a novel target to reduce BSM remodeling. PMID:22500186

Miglino, Nicola; Roth, Michael; Lardinois, Didier; Tamm, Michael; Borger, Peter

2012-01-01

41

Calreticulin Expression Is Associated with Androgen Regulation of the Sensitivity to Calcium Ionophore-induced Apoptosis in LNCaP Prostate Cancer Cells1  

Microsoft Academic Search

Calreticulin has been identified previously as one of the androgen- response genes in the prostate. The role of calreticulin in androgen action was studied using androgen-sensitive LNCaP and androgen-insensitive PC-3 human prostate cancer cell lines. Calreticulin appears to be a primary androgen-response gene in cultured LNCaP cells because andro- gen induction of calreticulin mRNA resists protein synthesis inhibition. Calreticulin is

Ning Zhu; Zhou Wang

1999-01-01

42

The polypeptide binding conformation of calreticulin facilitates its cell-surface expression under conditions of endoplasmic reticulum stress.  

PubMed

We define two classes of calreticulin mutants that retain glycan binding activity; those that display enhanced or reduced polypeptide-specific chaperone activity, due to conformational effects. Under normal conditions, neither set of mutants significantly impacts the ability of calreticulin to mediate assembly and trafficking of major histocompatibility complex class I molecules, which are calreticulin substrates. However, in cells treated with thapsigargin, which depletes endoplasmic reticulum calcium, major histocompatibility complex class I trafficking rates are accelerated coincident with calreticulin secretion, and detection of cell-surface calreticulin is dependent on its polypeptide binding conformations. Together, these findings identify a site on calreticulin that is an important determinant of the induction of its polypeptide binding conformation and demonstrate the relevance of the polypeptide binding conformations of calreticulin to endoplasmic reticulum stress-induced interactions. PMID:21075854

Jeffery, Elise; Peters, Larry Robert; Raghavan, Malini

2011-01-28

43

Expression and thermotolerance of calreticulin during pollen development in tobacco  

Microsoft Academic Search

Glycoproteins 50, 55, 59 and 64 kDa with affinity to the lectin ConA occurring abundantly in mature tobacco pollen were shown\\u000a to exhibit high tolerance against heating at 90°C for 30°min. The 59 kDa glycoprotein (GP59) was isolated by affinity chromatography\\u000a on ConA-agarose followed by 2D-electrophoresis and identified by MS analysis as tobacco calreticulin with approximate pI 4.2.\\u000a Identification of the protein

Petra Hrubá; David Honys; Jaroslav Tupý

2005-01-01

44

Molecular cloning and characterization of a calreticulin cDNA from the pinewood nematode Bursaphelenchus xylophilus.  

PubMed

The cloning and characterization of a cDNA encoding a calreticulin from the pinewood nematode Bursaphelenchus xylophilus is described herein. The full-length cDNA (Bx-crt-1) contained a 1200 bp open reading frame that could be translated to a 399 amino acid polypeptide. The deduced protein contained highly conserved regions of a calreticulin gene and had 66.2-70.1% amino acid sequence identity to other calreticulin sequences from nematodes. RNAi, RT-PCR amplification, and southern blot suggest that Bx-crt-1 may be important for the development of B. xylophilus. PMID:21371475

Li, Xundong; Zhuo, Kan; Luo, Mei; Sun, Longhua; Liao, Jinling

2011-06-01

45

Calreticulin expression is reduced in high-grade ovarian serous carcinoma effusions compared with primary tumors and solid metastases.  

PubMed

The objective of this study was to analyze the expression and clinical role of calreticulin, a multifunctional Ca(2+)-binding chaperone of the endoplasmic reticulum, in advanced-stage high-grade serous ovarian carcinoma. Cellular calreticulin messenger RNA (mRNA) and protein expression was investigated in 102 and 56 tumors, respectively, using reverse transcriptase polymerase chain reaction and Western blotting. Secreted calreticulin level was further analyzed in 31 effusion supernatants. Results were analyzed for association with anatomical site and clinicopathologic parameters, including survival. Calreticulin mRNA and protein were detected in 101 of 102 and 55 of 56 tumors, respectively. Calreticulin mRNA was overexpressed in solid metastases (n = 15) compared with effusions (n = 55) and primary carcinomas (n = 32; P = .009), whereas protein expression was significantly higher in solid metastases and primary carcinomas compared with effusion specimens (P = .007). Secreted calreticulin levels were higher in peritoneal compared with pleural effusions (P = .02). Higher cellular calreticulin protein expression in effusions was associated with better response to chemotherapy at diagnosis (P = .037). Calreticulin mRNA and protein expression was unrelated to patient survival. In conclusion, calreticulin is frequently expressed in serous ovarian carcinoma cells at all anatomical sites, but expression is reduced in effusions. Calreticulin protein levels in effusions may be predictive of chemotherapy response at diagnosis. PMID:24060004

Vaksman, Olga; Davidson, Ben; Tropé, Claes; Reich, Reuven

2013-12-01

46

Calreticulin: a new horizon for the testing and treatment of myeloproliferative neoplasms.  

PubMed

The recent discovery of mutations of the gene calreticulin has allowed raising the proportion of patients with essential thrombocythemia and primary myelofibrosis with known mutational abnormality up to 85-90%. Knowledge of the mechanisms by which mutated calreticulin underlie a myeloproliferative neoplasm as well as the clinical and therapeutic implications is just at the very beginning, and exciting times await research in this field. PMID:24849893

Guglielmelli, Paola; Bartalucci, Niccolò; Rotunno, Giada; Vannucchi, Alessandro M

2014-08-01

47

Entamoeba histolytica calreticulin: an endoplasmic reticulum protein expressed by trophozoites into experimentally induced amoebic liver abscesses  

Microsoft Academic Search

Entamoeba histolytica calreticulin (EhCRT) is remarkably immunogenic in humans (90–100% of invasive amoebiasis patients). Nevertheless, the study of calreticulin\\u000a in this protozoan is still in its early stages. The exact location, biological functions, and its role in pathogenesis are\\u000a yet to be fully understood. The aim of the present work is to determine the location of EhCRT in virulent trophozoites

Enrique González; Maria del Carmen García de Leon; Isaura Meza; Rodolfo Ocadiz-Delgado; Patricio Gariglio; Angelica Silva-Olivares; Silvia Galindo-Gómez; Mineko Shibayama; Patricia Morán; Alicia Valadez; Angelica Limón; Liliana Rojas; Eric G. Hernández; René Cerritos; Cecilia Ximenez

2011-01-01

48

Calreticulin is a B cell molecular target in some gastrointestinal malignancies.  

PubMed

Calreticulin, upon translocation to the cell surface, plays a critical role in the recognition of tumour cells and in experimentally induced cellular anti-tumour immunity. However, less is known about anti-calreticulin antibodies and their role in malignancies. Using enzyme-linked immunosorbent assay (ELISA), we found immunoglobulin (Ig)A and/or IgG anti-calreticulin antibodies in sera of approximately 63% of patients with hepatocellular carcinoma (HCC), 57% of patients with colorectal adenocarcinoma (CRA) and 47% of patients with pancreatic adenocarcinoma (PACA), while healthy controls, patients with viral hepatitis C and with chronic pancreatitis reached only 2%, 20% and 31% seropositivity, respectively. We found significantly elevated mean levels of IgA anti-calreticulin antibodies (P < 0.001) in patients with HCC (78.7 +/- 52.3 AU, mean +/- standard deviation), PACA (66.5 +/- 30.9 AU) and CRA (61.8 +/- 25.8 AU) when compared to healthy controls (41.4 +/- 19.2 AU). Significantly elevated mean levels of IgG anti-calreticulin antibodies (P < 0.001) were detected in patients with HCC (121.9 +/- 94.2 AU), gall bladder adenocarcinoma (118.4 +/- 80.0 AU) and PACA (88.7 +/- 55.6 AU) when compared to healthy controls (56.7 +/- 22.9 AU). Pepscan analysis revealed a large number of antigenic epitopes of calreticulin recognized by both IgA and IgG antibodies of patients with HCC and PACA, indicating robust systemic immune response. Moreover, significantly elevated levels of antibodies against peptide KGEWKPRQIDNP (P < 0.001) in these patients, tested by ELISA, confirmed the distinct character of antibody reactivity against calreticulin. The high occurrence and specificity of serum anti-calreticulin autoantibodies in the majority of patients with some gastrointestinal malignancies provide the evidence for their possible clinical relevance. PMID:20030668

Pekáriková, A; Sánchez, D; Palová-Jelínková, L; Simsová, M; Benes, Z; Hoffmanová, I; Drastich, P; Janatková, I; Mothes, T; Tlaskalová-Hogenová, H; Tucková, L

2010-05-01

49

Calreticulin expression in plant cells: developmental regulation, tissue specificity and intracellular distribution  

Microsoft Academic Search

.   The tissue-specific expression pattern and the intracellular distribution of the Ca2+-binding protein calreticulin at the mRNA and protein levels have been studied during somatic and zygotic embryogenesis of\\u000a Nicotiana plumbaginifolia Viv. A full-length cDNA sequence encoding calreticulin was isolated from a ? Zap cDNA library from early developmental stages\\u000a of somatic embryogenesis. The deduced amino acid sequence of the

Nikolai Borisjuk; Leonid Sitailo; Klaus Adler; Ludmilla Malysheva; Annegret Tewes; Ludmilla Borisjuk; Renate Manteuffel

1998-01-01

50

Aberrant calreticulin expression is involved in the dedifferentiation of dedifferentiated liposarcoma.  

PubMed

Liposarcomas are a representative group of soft tissue sarcomas with variably hampered adipogenesis, which is most exemplified by its dedifferentiated subtype. However, the factor(s) responsible for inhibiting adipocyte differentiation remains unknown. A recent gene expression profiling study identified several unique genes that were highly expressed in dedifferentiated liposarcoma, and the gene encoding calreticulin (CALR), a major Ca(2+)-buffering protein that can inhibit adipocyte differentiation, was found to be overexpressed. Thus, we investigated the expression of calreticulin in 45 cases of liposarcomas, including 15 dedifferentiated tumors, at both the protein and mRNA levels. Immunohistochemically, calreticulin was consistently expressed in the dedifferentiated areas of dedifferentiated liposarcomas and commonly observed in atypical stromal cells and/or lipoblasts in the well-differentiated areas (87%), whereas large vacuolated adipocytic cells in either the tumors or normal fat were essentially negative. These results were further supported by the findings of Western blot and quantitative RT-PCR analyses. Although abnormalities in 19p13.1-13.2 where CALR is localized were uncommon in the dedifferentiated liposarcomas examined by fluorescence in situ hybridization, expression of miR-1257, a putative microRNA that targets calreticulin, was suppressed in the dedifferentiated subtype. The down-regulation of calreticulin by small-interfering RNA could induce adipogenesis in dedifferentiated liposarcoma cells and reduce cell proliferation. Our results therefore suggest that aberrantly expressed calreticulin in dedifferentiated liposarcoma is involved in its dedifferenitation and/or tumor progression. PMID:22429966

Hisaoka, Masanori; Matsuyama, Atsuji; Nakamoto, Mitsuhiro

2012-05-01

51

Calreticulin Is the Major Ca 2+ Storage Protein in the Endoplasmic Reticulum of the Pea Plant ( Pisum sativum)  

Microsoft Academic Search

A 56kDa protein with high similarity in its N-terminal amino acid sequence to animal calreticulin and 100% homology with the N-terminal amino acids of spinach calreticulin has been identified in seeds of the pea plant (Pisum sativum). A new purification procedure is described by which the calreticulin-like protein was selectively solubilized by incubation with deoxycholate and HgCl2 from microsomes enriched

A. M. Hassan; C. Wesson; W. R. Trumble

1995-01-01

52

The Structure of Calreticulin C-terminal Domain Is Modulated by Physiological Variations of Calcium Concentration*  

PubMed Central

Calreticulin is an abundant endoplasmic reticulum resident protein that fulfills at least two basic functions. Firstly, due to its ability to bind monoglucosylated high mannose oligosaccharides, calreticulin is a central component of the folding quality control system of glycoproteins. On the other hand, thanks to its capacity to bind high amounts of calcium, calreticulin is one of the main calcium buffers in the endoplasmic reticulum. This last activity resides on a highly negatively charged domain located at the C terminus. Interestingly, this domain has been proposed to regulate the intracellular localization of calreticulin. Structural information for this domain is currently scarce. Here we address this issue by employing a combination of biophysical techniques and molecular dynamics simulation. We found that calreticulin C-terminal domain at low calcium concentration displays a disordered structure, whereas calcium addition induces a more rigid and compact conformation. Remarkably, this change develops when calcium concentration varies within a range similar to that taking place in the endoplasmic reticulum upon physiological fluctuations. In addition, a much higher calcium concentration is necessary to attain similar responses in a peptide displaying a randomized sequence of calreticulin C-terminal domain, illustrating the sequence specificity of this effect. Molecular dynamics simulation reveals that this ordering effect is a consequence of the ability of calcium to bring into close proximity residues that lie apart in the primary structure. These results place calreticulin in a new setting in which the protein behaves not only as a calcium-binding protein but as a finely tuned calcium sensor. PMID:20018892

Giraldo, Ana María Villamil; Medus, Máximo Lopez; Lebrero, Mariano Gonzalez; Pagano, Rodrigo S.; Labriola, Carlos A.; Landolfo, Lucas; Delfino, José M.; Parodi, Armando J.; Caramelo, Julio J.

2010-01-01

53

Autocrine regulation of T cell motility by calreticulin-thrombospondin-1 interaction.  

PubMed

The mechanisms regulating T lymphocyte migration within the extracellular matrix are not understood. We show in this study that the thrombospondin-1 binding site of calreticulin, spanning aa 19-32, is a major triggering factor for T cell motility and migration within a three-dimensional collagen type 1 matrix, and that exogenous motogenic factors such as chemokines can stimulate migration via a calreticulin-thrombospondin-1 pathway. Endogenous calreticulin binding to the N-terminal domain of endogenous thrombospondin-1 elicited a motogenic signal to the T cells through the C-terminal domain of thrombospondin-1 and its cell surface receptor integrin-associated protein (CD47). Our data further revealed that thrombospondin-1 was expressed on the cell surface with a high turnover, and that PI3K and the Janus family of tyrosine kinases were required for T cell motility mediated through calreticulin, thrombospondin-1, and CD47. These results unveil an autocrine mechanism of calreticulin-thrombospondin-1-CD47 interaction for the control of T cell motility and migration within three-dimensional extracellular matrix substrata. PMID:15634883

Li, Shu Shun; Forslöw, Anna; Sundqvist, Karl-Gösta

2005-01-15

54

An autoantibody-mediated immune response to calreticulin isoforms in pancreatic cancer.  

PubMed

The identification of circulating tumor antigens or their related autoantibodies provides a means for early cancer diagnosis as well as leads for therapy. We have used a proteomic approach to identify proteins that commonly induce a humoral response in pancreatic cancer. Aliquots of solubilized proteins from a pancreatic cancer cell line (Panc-1) were subjected to two-dimensional PAGE, followed by Western blot analysis in which sera of individual patients were tested for primary antibodies. Sera from 36 newly diagnosed patients with pancreatic cancer, 18 patients with chronic pancreatitis, 33 patients with other cancers, and 15 healthy subjects were analyzed. Autoantibodies were detected against either one or two calreticulin isoforms identified by mass spectrometry in sera from 21 of 36 patients with pancreatic cancer. One of 18 chronic pancreatitis patients and 1 of 15 healthy controls demonstrated autoantibodies to calreticulin isoform 1; none demonstrated autoantibodies to isoform 2. None of the sera from patients with colon cancer exhibited reactivity against either of these two proteins. One of 14 sera from lung adenocarcinoma patients demonstrated autoantibodies to calreticulin isoform 1; 2 of 14 demonstrated autoantibodies to isoform 2. Immunohistochemical analysis of calreticulin in pancreatic/ampullary tumor tissue arrays using an isoform nonspecific antibody revealed diffuse and consistent cytoplasmic staining in the neoplastic epithelial cells of the pancreatic and ampullary adenocarcinomas. The detection of autoantibodies to calreticulin isoforms may have utility for the early diagnosis of pancreatic cancer. PMID:15289361

Hong, Su-Hyung; Misek, David E; Wang, Hong; Puravs, Eric; Giordano, Thomas J; Greenson, Joel K; Brenner, Dean E; Simeone, Diane M; Logsdon, Craig D; Hanash, Samir M

2004-08-01

55

Roles for Calreticulin and a Novel Glycoprotein, Tapasin, in the Interaction of MHC Class I Molecules with TAP  

Microsoft Academic Search

Assembly of MHC class I–?2 microglobulin (?2m) dimers in the endoplasmic reticulum involves two chaperones. Calnexin has previously been shown to interact with free class I heavy chains. Here, we show that the related chaperone, calreticulin, binds human class I–?2m dimers prior to peptide loading. Calreticulin remains associated with at least a subset of class I molecules when they, in

Bhanu Sadasivan; Paul J Lehner; Bodo Ortmann; Thomas Spies; Peter Cresswell

1996-01-01

56

Leveraging the Immune System during Chemotherapy: Moving Calreticulin to the Cell Surface Converts Apoptotic Death from ''Silent'' to Immunogenic  

Microsoft Academic Search

In contrast to prior belief, tumor cell apoptosis is not necessarily silent but can be immunogenic. By tracing how anthracyclines and ;-irradiation trigger immunogenic cell deaths, we found that they were causally connected to the exposure of calreticulin on the tumor cell surface, before apoptosis in the tumor cell itself occurred. Furthermore, we showed that calreticulin exposure was necessary and

Michel Obeid; Theocharis Panaretakis; Antoine Tesniere; Nick Joza; Roberta Tufi; Lionel Apetoh; Francois Ghiringhelli; Laurence Zitvogel

2007-01-01

57

Immunological Activity Difference between Native Calreticulin Monomers and Oligomers  

PubMed Central

We have recently demonstrated that the greatly increased immunological activities of recombinant murine calreticulin (rCRT) are largely attributed to its self-oligomerization. Although native CRT (nCRT) can also oligomerize under stress conditions in vitro, whether this phenomenon could occur inside cells and the immunological activity difference between nCRT monomers and oligomers remained unclear. In this study, we illustrated the formation of CRT oligomers in tranfectant cells under “heat & low pH” (42°C/pH 6.5) condition. The mixture of nCRT oligomers and monomers (OnCRT) was obtained after 3 hr treatment of murine monomeric nCRT (MnCRT) under similar condition (42°C/pH 5.0) in vitro. The OnCRT thus obtained was better recognized by 2 monoclonal Abs from mice that had been immunized with oligomeric rCRT. Unlike MnCRT, OnCRT was able to elicit CRT-specific IgG production in mice. OnCRT also stimulated bone-marrow derived dendritic cells (BMDCs) to secrete significantly higher levels of TNF-?, IL-6 and IL-12p40 than did MnCRT in vitro. We postulate that oligomerization of soluble CRT may occur under certain pathophysiological conditions (e.g. ultrahyperpyrexia) and the resultant oligomers may exhibit exaggerated immunostimulating activities, thereby affiliating the inflammatory responses in vivo. PMID:25171171

He, Mi-chun; Wang, Jun; Wu, Jian; Gong, Fang-yuan; Hong, Chao; Xia, Yun; Zhang, Li-juan; Bao, Wan-rong; Gao, Xiao-Ming

2014-01-01

58

A role for calreticulin in the pathogenesis of rheumatoid arthritis.  

PubMed

Calreticulin (CRT) plays a role in the clearance of dying cells and has been implicated in autoimmunity. Recent evidence indicates that cell surface CRT (csCRT) acts as a signal transducing receptor for the rheumatoid arthritis (RA) shared epitope (SE). The SE binding site on CRT has been mapped to amino acid residues 217-223 in the P-domain. Upon interaction with dendritic cells (DCs), the SE activates potent immune regulatory events. In CD8?(+) DCs, which express higher abundance of csCRT, the SE inhibits the tolerogenic enzyme indoleamine 2,3 dioxygenase with resultant inhibition of regulatory T (Treg) cell differentiation. In CD8?(-) DCs, the SE ligand increases secretion of IL-6 and IL-23 and facilitates generation of Th17 cells, a T cell subset known to play a role in autoimmunity. On the basis of these recent findings, we discuss the possibility that the csCRT may play a pathogenic role in RA by transducing SE-activated Th17-polarizing signals. PMID:20958321

Holoshitz, Joseph; De Almeida, Denise E; Ling, Song

2010-10-01

59

Calreticulin as a potential diagnostic biomarker for lung cancer.  

PubMed

Calreticulin (CRT) is an endoplasmic reticulum luminal Ca(2+)-binding chaperone protein. By immunizing mice with recombinant fragment (rCRT/39-272), six clones of monoclonal antibodies (mAbs) were generated and characterized. Based on these mAbs, a microplate chemiluminescent enzyme immunoassay (CLEIA) system with a measured limit of detection of 0.09 ng/ml was developed. Using this CLEIA system, it was found that soluble CRT (sCRT) level in serum samples from 58 lung cancer patients was significantly higher than that from 40 healthy individuals (only 9 were detectable, P < 0.0001). Among them, serum sCRT in the small cell lung cancer was lower than that in adenocarcinoma (P = 0.0085), while both were lower than that in the squamous cell carcinoma (P = 0.013, P = 0.0012, respectively). Moreover, it was found that sCRT in sera from the patients after chemotherapy was higher than that from the patients without chemotherapy (P = 0.042). Further study by immunohistochemistry showed that CRT was also highly expressed in the cytoplasm and on the membrane of the lung cancer cells, while there was a trace amount of CRT expression in normal lung cells. Correspondingly, the expression level of CRT on lung cancer cell membrane was associated with the tumor pathological grade. This study demonstrates that sCRT concentration in sera of lung cancer patients is higher than that in sera of healthy individuals, and CRT expression level on lung cancer cell membrane is associated with tumor pathological classification and grade. These findings suggest that CRT may be used as a biomarker in lung cancer prediction and diagnosis. PMID:22083347

Liu, Rongrong; Gong, Jiuyu; Chen, Jun; Li, Qi; Song, Chaojun; Zhang, Jian; Li, Yongming; Liu, Zhijia; Dong, Yun; Chen, Lihua; Jin, Boquan

2012-06-01

60

Citrullinated calreticulin potentiates rheumatoid arthritis shared epitope signaling  

PubMed Central

Objective Citrullinated proteins are immunogenic in rheumatoid arthritis (RA), particularly in patients that carry shared epitope (SE)-coding HLA-DRB1 alleles. The mechanism underlying this association is unknown. We have previously identified SE as a ligand that interacts with cell surface calreticulin (CRT) and activates immune dysregulation. The objective of this study was to determine the effect of CRT citrullination on SE signaling. Methods CRT-SE binding affinity was measured by surface plasmon resonance. The role of individual CRT arginine residues was determined by site-directed mutagenesis. Nitric oxide levels were measured using a fluorochrome-based assay. CRT citrullination in synovial tissues and cell cultures was determined by 2-dimensional gel electrophoresis, immunoblotting and mass spectrometry techniques. Results Synovial tissues and fibroblast-like synoviocytes from RA patients were found to express higher abundance of citrullinated CRT compared to OA samples. Citrullinated CRT showed more robust interaction with the SE ligand, and transduced SE signaling at a 10,000-fold higher potency, compared to non-citrullinated CRT. Site-directed mutation analysis identified Arg205, which is spatially adjacent to the SE binding site in the CRT P-domain, as a dominant inhibitor of SE-CRT interaction and signaling, while a more remote arginine residue, Arg261 was found to enhance these SE functions. Conclusion Citrullinated CRT is over-abundant in the RA synovium, and potentiates SE-activated signaling in vitro. These findings could introduce a new mechanistic model of gene-environment interaction in RA. PMID:23233327

Ling, Song; Cline, Erika N; Haug, Timothy S; Fox, David A; Holoshitz, Joseph

2012-01-01

61

Calreticulin regulates transforming growth factor-?-stimulated extracellular matrix production.  

PubMed

Endoplasmic reticulum (ER) stress is an emerging factor in fibrotic disease, although precise mechanisms are not clear. Calreticulin (CRT) is an ER chaperone and regulator of Ca(2+) signaling up-regulated by ER stress and in fibrotic tissues. Previously, we showed that ER CRT regulates type I collagen transcript, trafficking, secretion, and processing into the extracellular matrix (ECM). To determine the role of CRT in ECM regulation under fibrotic conditions, we asked whether CRT modified cellular responses to the pro-fibrotic cytokine, TGF-?. These studies show that CRT-/- mouse embryonic fibroblasts (MEFs) and rat and human idiopathic pulmonary fibrosis lung fibroblasts with siRNA CRT knockdown had impaired TGF-? stimulation of type I collagen and fibronectin. In contrast, fibroblasts with increased CRT expression had enhanced responses to TGF-?. The lack of CRT does not impact canonical TGF-? signaling as TGF-? was able to stimulate Smad reporter activity in CRT-/- MEFs. CRT regulation of TGF-?-stimulated Ca(2+) signaling is important for induction of ECM. CRT-/- MEFs failed to increase intracellular Ca(2+) levels in response to TGF-?. NFAT activity is required for ECM stimulation by TGF-?. In CRT-/- MEFs, TGF-? stimulation of NFAT nuclear translocation and reporter activity is impaired. Importantly, CRT is required for TGF-? stimulation of ECM under conditions of ER stress, as tunicamycin-induced ER stress was insufficient to induce ECM production in TGF-? stimulated CRT-/- MEFs. Together, these data identify CRT-regulated Ca(2+)-dependent pathways as a critical molecular link between ER stress and TGF-? fibrotic signaling. PMID:23564462

Zimmerman, Kurt A; Graham, Lauren V; Pallero, Manuel A; Murphy-Ullrich, Joanne E

2013-05-17

62

Gene Transfer of Vasostatin, a Calreticulin Fragment, into Neuroendocrine Tumor Cells Results in Enhanced Malignant Behavior  

Microsoft Academic Search

Vasostatin, a fragment of calreticulin, was transfected in the BON cell line to evaluate the feasibility of using it for gene therapy in neuroendocrine tumors. Vasostatin transfected cells were subcutaneously inoculated in nude mice. Burkitt lymphoma cell line, CA46, colorectal adenocarcinoma cell line, SW480, as well as endothelial cells PAE and SVEC4 were used for evaluating the function of vasostatin.

Minghui Liu; Hassan Imam; Kjell Öberg; Yinghua Zhou

2005-01-01

63

Calreticulin promotes folding/dimerization of human lipoprotein lipase expressed in insect cells (sf21).  

PubMed

Lipoprotein lipase (LPL) is a non-covalent, homodimeric, N-glycosylated enzyme important for metabolism of blood lipids. LPL is regulated by yet unknown post-translational events affecting the levels of active dimers. On co-expression of LPL with human molecular chaperones, we found that calreticulin had the most pronounced effects on LPL activity, but calnexin was also effective. Calreticulin caused a 9-fold increase in active LPL, amounting to about 50% of the expressed LPL protein. The total expression of LPL protein was increased less than 20%, and the secretion rates for active and inactive LPL were not significantly changed by the chaperone. Thus, the main effect was an increased specific activity of LPL both in cells and media. Chromatography on heparin-Sepharose and sucrose density gradient centrifugation demonstrated that most of the inactive LPL was monomeric and that calreticulin promoted formation of active dimers. Higher oligomers of inactive LPL were present in cell extracts, but only monomers and dimers were secreted to the medium. Interaction between LPL and calreticulin was demonstrated, and the effect of the chaperone was prevented by castanospermine, an inhibitor of N-glycan glucose trimming. Our data indicate an important role of endoplasmic reticulum-based chaperones for the folding/dimerization of LPL. PMID:12740382

Zhang, Liyan; Wu, Gengshu; Tate, Christopher G; Lookene, Aivar; Olivecrona, Gunilla

2003-08-01

64

Retrotranslocation of the Chaperone Calreticulin from the Endoplasmic Reticulum Lumen to the Cytosol  

Microsoft Academic Search

Polypeptide folding and quality control in the endoplasmic reticulum (ER) are mediated by protein chap- erones, including calreticulin (CRT). ER localization of CRT is specified by two types of targeting signals, an N-terminal hydrophobic signal sequence that directs insertion into the ER and a C-terminal KDEL sequence that is responsible for retention in the ER. CRT has been implicated in

Nima Afshar; Ben E. Black; Bryce M. Paschal

2005-01-01

65

Calreticulin requires an ancillary adjuvant for the induction of efficient cytotoxic T cell responses.  

PubMed

Molecular chaperones stimulate the immune system to induce both protective immune responses and therapeutic tumor rejection. However, the underlying basis for this immunogenic activity is not well understood. A variety of chaperones, including calreticulin, hsp70 and grp94, function as vehicles to efficiently traffic associated peptides into professional antigen presenting cells. Importantly, these chaperones have also been proposed to function as adjuvants by stimulating the dendritic cell activation and co-stimulatory responses required to elicit peptide-specific CD8(+) T cell cytolytic activity. The efficacy of chaperone-mediated tumor rejection has been attributed to the ability of chaperones to function in both of these capacities. However, purified calreticulin has not previously been assessed for its ability to elicit DC maturation and, moreover, recent data indicates that it is not efficient at inducing Nf-kappaB activity which often accompanies or stimulates DC maturation. Here we use two complementary methods to produce endotoxin-free calreticulin and demonstrate that it does not measurably mature or activate dendritic cells both in vitro and in vivo. Additionally, a calreticulin/peptide complex required the addition of an exogenous adjuvant to elicit in vivo cytotoxic CD8(+) T cell responses. These data are discussed with respect to current models for chaperone-derived immune responses and in regard to rational vaccine design. PMID:17936359

Bak, S Peter; Amiel, Eyal; Walters, Julie Jo; Berwin, Brent

2008-03-01

66

J Biol Chem. Author manuscript Post-translational arginylation of calreticulin: a new isospecies of  

E-print Network

isospecies of calreticulin component of stress granules Decca Maria B. 1 , Carpio Marcos A. 1 , Bosc Christophe 2 , Galiano Mauricio R. 1 , Job Didier 2 , Andrieux Annie 2 , Hallak Marta E. 1 * Centro de). Under stress conditions, arginylated-CRT was found associated to stress granules. These results suggest

Paris-Sud XI, Université de

67

Calreticulin-dependent recycling in the early secretory pathway mediates optimal peptide loading of MHC class I molecules.  

PubMed

Calreticulin is a lectin chaperone of the endoplasmic reticulum (ER). In calreticulin-deficient cells, major histocompatibility complex (MHC) class I molecules travel to the cell surface in association with a sub-optimal peptide load. Here, we show that calreticulin exits the ER to accumulate in the ER-Golgi intermediate compartment (ERGIC) and the cis-Golgi, together with sub-optimally loaded class I molecules. Calreticulin that lacks its C-terminal KDEL retrieval sequence assembles with the peptide-loading complex but neither retrieves sub-optimally loaded class I molecules from the cis-Golgi to the ER, nor supports optimal peptide loading. Our study, to the best of our knowledge, demonstrates for the first time a functional role of intracellular transport in the optimal loading of MHC class I molecules with antigenic peptide. PMID:19851281

Howe, Christopher; Garstka, Malgorzata; Al-Balushi, Mohammed; Ghanem, Esther; Antoniou, Antony N; Fritzsche, Susanne; Jankevicius, Gytis; Kontouli, Nasia; Schneeweiss, Clemens; Williams, Anthony; Elliott, Tim; Springer, Sebastian

2009-12-01

68

Identification of common epitopes on gliadin, enterocytes, and calreticulin recognised by antigliadin antibodies of patients with coeliac disease  

Microsoft Academic Search

BackgroundSera of patients with coeliac disease, containing IgA and IgG antigliadin antibodies (AGA) and various IgA autoantibodies, react with isolated enterocytes. AGA cross react with enterocyte antigens, one of which has been identified as calreticulin.AimsTo characterise the antigenic structures of gliadin, enterocytes, and calreticulin recognised by AGA from patients with active coeliac disease.MethodsAGA were isolated from sera of nine patients

S Krupic?ková; L Tuc?ková; Z Flegelová; M Michalak; J R F Walters; A Whelan; J Harries; J Vencovsky?; H Tlaskalová-Hogenová

1999-01-01

69

Molecular characterization of calreticulin from Anopheles stephensi midgut cells and functional assay of the recombinant calreticulin with Plasmodium berghei ookinetes.  

PubMed

Transmission blocking vaccines (TBVs) that target the antigens on the midgut epithelium of Anopheles mosquitoes are among the promising tools for the elimination of the malaria parasite. Characterization and analysis of effective antigens is the first step to design TBVs. Calreticulin (CRT), a lectin-like protein, from Anopheles albimanus midgut, has shown antigenic features, suggesting a promising and novel TBV target. CRT is a highly conserved protein with similar features in vertebrates and invertebrates including anopheline. We cloned the full-length crt gene from malaria vector, Anopheles stephensi (AsCrt) and explored the interaction of recombinant AsCrt protein, expressed in a prokaryotic system (pGEX-6p-1), with surface proteins of Plasmodium berghei ookinetes by immunofluorescence assay. The cellular localization of AsCrt was determined using the baculovirus expression system. Sequence analysis of the whole cDNA of AsCrt revealed that AsCrt contains an ORF of 1221 bp. The amino acid sequence of AsCrt protein obtained in this study showed 64% homology with similar protein in human. The AsCrt shares the most common features of CRTs from other species. This gene encodes a 406 amino-acid protein with a molecular mass of 46 kDa, which contains a predicted 16 amino-acid signal peptides, conserved cysteine residues, a proline-rich region, and highly acidic C-terminal domain with endoplasmic reticulum retrieval sequence HDEL. The production of GST-AsCrt recombinant protein was confirmed by Western blot analysis using an antibody against the GST protein. The FITC-labeled GST-AsCrt exhibited a significant interaction with P. berghei ookinete surface proteins. Purified recombinant GST-AsCrt, labeled with FITC, displayed specific binding to the surface of P. berghei ookinetes in comparison with control. Moreover, the expression of AsCrt in baculovirus expression system indicated that AsCrt was localized on the surface of Sf9 cells. Our results suggest that AsCrt could be utilized as a potential target for future studies in TBV area for malaria control. PMID:25150160

Borhani Dizaji, Nahid; Basseri, Hamid Reza; Naddaf, Saied Reza; Heidari, Mansour

2014-10-25

70

Calreticulin inhibits glucocorticoid– but not cAMP–sensitive expression of tyrosine aminotransferase gene in cultured McA–RH7777 hepatocytes  

Microsoft Academic Search

Calreticulin is a ubiquitously expressed Ca2+ binding protein of the endoplasmic reticulum which inhibits DNA binding and transcriptional activation by steroid hormone receptors. In this study the effects of calreticulin on tyrosine aminotransferase (TAT) gene expression in cultured McA–RH7777 hepatocytes was investigated. McA–RH7777 cells were stably transfected with calreticulin expression vector to generate cells overexpressing the protein. The transcriptional activity

Kimberly Burns; Michal Opas; Marek Michalak

1997-01-01

71

Calreticulin is expressed on the cell surface of activated human peripheral blood T lymphocytes in association with major histocompatibility complex class I molecules.  

PubMed

Calreticulin is an endoplasmic reticulum resident molecule known to be involved in the folding and assembly of major histocompatibility complex (MHC) class I molecules. In the present study, expression of calreticulin was analyzed in human peripheral blood T lymphocytes. Pulse-chase experiments in [35S]methionine-labeled T cell blasts showed that calreticulin was associated with several proteins in the endoplasmic reticulum and suggested that it was expressed at the cell surface. Indeed, the 60-kDa calreticulin was labeled by cell surface biotinylation and precipitated from the surface of activated T cells together with a protein with an apparent molecular mass of 46 kDa. Cell surface expression of calreticulin by activated T lymphocytes was further confirmed by immunofluorescence and flow cytometry, studies that showed that both CD8+ and CD4+ T cells expressed calreticulin in the plasma membrane. Low amounts of cell surface calreticulin were detected in resting T lymphocytes. By sequential immunoprecipitation using the conformation independent monoclonal antibody HC-10, we provided evidence that the cell surface 46-kDa protein co-precipitated with calreticulin is unfolded MHC I. These results show for the first time that after T cell activation, significant amounts of calreticulin are expressed on the T cell surface, where they are found in physical association with a pool of beta2-free MHC class I molecules. PMID:10358038

Arosa, F A; de Jesus, O; Porto, G; Carmo, A M; de Sousa, M

1999-06-11

72

Pyruvate dehydrogenase/sub b/ phosphatase inhibition by NADH and dihydrolipoamide along with effects of and capacity for binding the phosphatase to the bovine kidney transacetylase-protein X subcomplex  

SciTech Connect

NADH inhibits PDH/sub b/ phosphatase activity when /sup 32/P-PDH is associated with the intact complex but not when /sup 32/P-PDH is prepared free of other components of the complex. Addition of the transacetylase-protein X (E2-X) subcomplex both activated the phosphatase and restored NADH inhibition. Low levels of dihydrolipoyl dehydrogenase associated with the subcomplex might be required for NADH inhibition. Dihydrolipoamide gave inhibition of the phosphatase equivalent to NADH and the combination did not give additional inhibition suggesting a common mechanism. Pretreatment of phosphorylated complex and phosphatase with 2.0 mM dithiothreitol nearly eliminated inhibition of the phosphatase by NADH or dihydrolipoamide. Strong arsenite inhibition of phosphatase activity occurred only in the presence of NADH suggesting modification of thiols reduced by NADH can alter phosphatase activity. Only about 6 molecules of purified phosphatase could be activated by 1 molecule of E2-X subcomplex (initial velocities measured in 15s period). Since that corresponded to the number of protein X rather than E2 subunits, protein X may contribute to the Ca/sup 2 +/-dependent binding of the phosphatase. Since protein X also contains a lipoyl moiety, it may also contribute to NADH inhibition of the phosphatase.

Roche, T.E.; Rahmatullah, M.; Maher, J.

1986-05-01

73

Reduction of endoplasmic reticulum Ca2+ levels favors plasma membrane surface exposure of calreticulin  

Microsoft Academic Search

Some chemotherapeutic agents can elicit apoptotic cancer cell death, thereby activating an anticancer immune response that influences therapeutic outcome. We previously reported that anthracyclins are particularly efficient in inducing immunogenic cell death, correlating with the pre-apoptotic exposure of calreticulin (CRT) on the plasma membrane surface of anthracyclin-treated tumor cells. Here, we investigated the role of cellular Ca2+ homeostasis on CRT

R Tufi; T Panaretakis; K Bianchi; A Criollo; B Fazi; F Di Sano; A Tesniere; O Kepp; P Paterlini-Brechot; L Zitvogel; M Piacentini; G Szabadkai; G Kroemer

2008-01-01

74

In vivo pharmacokinetics of calreticulin S-domain, an inhibitor of the classical complement pathway  

Microsoft Academic Search

Inhibition of the complement system is potentially therapeutic in diseases where uncontrolled or overshooting complement activation plays a significant role in the pathogenesis of the disorder. Calreticulin (CRT) is a multifunctional protein whose cell-surface form (ectocalreticulin) is reported to be a C1q receptor. A 124-residue domain within CRT, the S-domain, binds to C1q, prevents the formation of C1 and so

Nicholas J. Lynch; Heiko Schneider; Robert B. Sim; Ulrich Bickel; Wilhelm J. Schwaeble

2002-01-01

75

The ins and outs of calreticulin: from the ER lumen to the extracellular space  

Microsoft Academic Search

Calreticulin was first isolated 26 years ago. Since its discovery as a minor Ca2+-binding protein of the sarcoplasmic reticulum, the appreciation of its importance has grown, and it is now recognized to be a multifunctional protein, most abundant in the endoplasmic reticulum (ER). The protein has well-recognized physiological roles in the ER as a molecular chaperone and Ca2+-signalling molecule. However,

Steven Johnson; Marek Michalak; Michal Opas; Paul Eggleton

2001-01-01

76

Mapping the complement C1q binding site in Haemonchus contortus calreticulin  

Microsoft Academic Search

Haemonchus contortus is an economically important gastrointestinal parasite of domestic animals. The parasite secretes calreticulin (CalR), a Ca++ binding protein which modulates the host immune response. One way by which this protein acts is by inhibiting the classical complement pathway by binding to complement C1q protein. Understanding CalR–C1q interaction is important to develop methods to enhance host immune response. In

S. Naresha; A. Suryawanshi; M. Agarwal; B. P. Singh; P. Joshi

2009-01-01

77

Characterization of Haemonchus contortus calreticulin suggests its role in feeding and immune evasion by the parasite  

Microsoft Academic Search

Haemonchus contortus, a gastrointestinal parasite of sheep and goat feeds on the blood of its host and causes bleeding at the biting site. In this report, we demonstrate that the Ca2+ binding protein, calreticulin (CalR), is present in excretory\\/secretory products of adult worms. The secreted CalR enhanced plasma coagulation time. Using recombinant fragments, this property has been mapped to C-terminal

Sajja Suchitra; Paritosh Joshi

2005-01-01

78

Effects of Humoral Immunity and Calreticulin Overexpression on Postoperative Course in Breast Cancer  

Microsoft Academic Search

The aim was to investigate whether the humoral immunity and overexpression of calreticulin in tumor tissue determined before\\u000a surgery, correlate with incidence of metastases in breast cancer patients within two years after operation. Before operation,\\u000a their humoral immunity and overexpression of caleticulin and Her-2\\/neu in tumor tissue were analyzed by immunohystochemistry.\\u000a In 23 patients with metastases in regionally lymph nodes,

Aleksandra Eri?; Zorica Jurani?; Zorka Milovanovi?; Ivan Markovi?; Mom?ilo Ini?; Nevenka Stanojevi?-Baki?; Vesna Vojinovi?-Golubovi?

2009-01-01

79

Epitopes of calreticulin recognised by IgA autoantibodies from patients with hepatic and coeliac disease  

Microsoft Academic Search

Calreticulin (CRT) was identified as a frequent target of serum autoantibodies (Ab) in various diseases, but anti-CRT Ab of IgA isotype were described only in coeliac (CLD) and some hepatic diseases. Employing ELISA with recombinant CRT we found significantly higher (P<0.001) levels of IgA anti-CRT Ab in sera of patients with primary biliary cirrhosis (PBC) (77.6±8.9 AU\\/mean±SE), autoimmune hepatitis (AIH)

Daniel Sánchez; Ludmila Tu?ková; Thomas Mothes; Wolfgang Kreisel; Zden?k Beneš; Helena Tlaskalová-Hogenová

2003-01-01

80

The co-translocation of ERp57 and calreticulin determines the immunogenicity of cell death  

Microsoft Academic Search

The exposure of calreticulin (CRT) on the plasma membrane can precede anthracycline-induced apoptosis and is required for cell death to be perceived as immunogenic. Mass spectroscopy, immunofluorescence and immunoprecipitation experiments revealed that CRT co-translocates to the surface with another endoplasmic reticulum-sessile protein, the disulfide isomerase ERp57. The knockout and knockdown of CRT or ERp57 inhibited the anthracycline-induced translocation of ERp57

T Panaretakis; N Joza; N Modjtahedi; A Tesniere; I Vitale; M Durchschlag; G M Fimia; O Kepp; M Piacentini; K-U Froehlich; P van Endert; L Zitvogel; F Madeo; G Kroemer

2008-01-01

81

The histone deacetylase inhibitor vorinostat induces calreticulin exposure in childhood brain tumour cells in vitro  

Microsoft Academic Search

Purpose  It has recently been recognised that anticancer chemotherapy can elicit an immunogenic form of apoptosis characterised by\\u000a the exposure of calreticulin (CRT) on the surface of dying tumour cells, entailing an immune response that contributes to\\u000a the therapeutic outcome. CRT exposure has been found to be induced by anthracyclins and oxaliplatin, but not by other proapoptotic\\u000a antineoplastic agents including etoposide,

Jürgen Sonnemann; Stephanie Greßmann; Sabine Becker; Susan Wittig; Mareike Schmudde; James F. Beck

2010-01-01

82

Calreticulin maintains the low threshold of peptide required for efficient antigen presentation  

Microsoft Academic Search

Calreticulin (CRT) plays a critical role in MHC class I antigen processing and elicits peptide-specific CD8(+) T cell responses against tumours when administered with peptides. However, how CRT contributes to class I antigen processing and the mechanism of its adjuvant effect in anti-tumour responses, remain to be elucidated. Here we show that reduced class I expression in CRT deficient cells

Hongmei Fu; Changzhen Liu; Barry Flutter; Hua Tao; Bin Gao

2009-01-01

83

Enhancement of vaccinia vaccine potency by linkage of tumor antigen gene to gene encoding calreticulin.  

PubMed

Vaccinia vaccines have become important vectors for antigen-specific immunotherapy. Calreticulin has been shown to enhance MHC class I presentation of linked peptide/protein and may be useful for antigen-specific cancer treatment. An innovative vaccine administering antigen linked to calreticulin via a vaccinia vector may generate a potent antigen-specific antitumor response. We tested the efficacy of linking calreticulin (CRT) to model antigen human papilloma virus type 16 (HPV-16) E7 in the context of a vaccinia vaccine (Vac-CRT/E7). Intraperitoneal vaccination of C57BL/6 mice with Vac-CRT/E7 led to a dramatic increase in E7-specific IFN-gamma-secreting CD8+ T cells and a potent antitumor effect against E7-expressing tumors compared to immunization with Vac-E7 or Vac-CRT. When compared to other chimeric vaccinia vaccines employing various intracellular targeting strategies previously developed in our lab, Vac-CRT/E7 elicited the highest number of E7-specific CD8+ T cells. Thus, vaccination with vaccinia expressing CRT linked to a tumor antigen may represent an advantageous strategy for cancer immunotherapy. PMID:15364449

Hsieh, Chia-Jung; Kim, Tae Woo; Hung, Chien-Fu; Juang, Jeremy; Moniz, Michelle; Boyd, David A K; He, Liangmei; Chen, Pei-Jer; Chen, Chien-Hung; Wu, T-C

2004-09-28

84

Calreticulin is the dominant pro-phagocytic signal on multiple human cancers and is counterbalanced by CD47  

PubMed Central

Under normal physiologic conditions, cellular homeostasis is partly regulated by balancing pro- and anti-phagocytic signals. CD47 is highly expressed on several human cancers including acute myeloid leukemia, non-Hodgkin lymphoma, and bladder cancer, allowing cancer cells to evade phagocytosis by the innate immune system. Blockade of CD47 with a monoclonal antibody enables phagocytosis of cancer cells and leads to in vivo tumor elimination, but leaves most normal cells unaffected. In order for target cells to be phagocytosed upon blockade of an anti-phagocytic signal, we postulate that the cells must also display a potent pro-phagocytic signal. Here we identify calreticulin as a pro-phagocytic signal highly expressed on the surface of several human cancers including acute myeloid and lymphoblastic leukemias, chronic myeloid leukemia, non-Hodgkin lymphoma (NHL), bladder cancer, glioblastoma, and ovarian cancer, but minimally expressed on most normal cells. Increased CD47 expression correlated with high calreticulin levels on cancer cells, and was necessary for protection from calreticulin-mediated phagocytosis. Phagocytosis induced by anti-CD47 antibody required the interaction of target cell calreticulin with its receptor low density lipoprotein-receptor related protein (LRP) on phagocytic cells, as blockade of the calreticulin/LRP interaction prevented anti-CD47 antibody mediated phagocytosis. Lastly, increased calreticulin expression was an adverse prognostic factor in diverse tumors including neuroblastoma, bladder cancer, and NHL. These findings identify calreticulin as the dominant pro-phagocytic signal on several human cancers, provide an explanation for the selective targeting of tumor cells by anti-CD47 antibody, and highlight the balance between pro- and anti-phagocytic signals in the immune evasion of cancer. PMID:21178137

Chao, Mark P.; Jaiswal, Siddhartha; Weissman-Tsukamoto, Rachel; Alizadeh, Ash A.; Gentles, Andrew J.; Volkmer, Jens; Weiskopf, Kipp; Willingham, Stephen B.; Raveh, Tal; Park, Christopher Y.; Majeti, Ravindra; Weissman, Irving L.

2014-01-01

85

Major histocompatibility complex class I molecules expressed with monoglucosylated N-linked glycans bind calreticulin independently of their assembly status.  

PubMed

The assembly of major histocompatibility complex (MHC) class I molecules with peptides in the endoplasmic reticulum (ER) is a critical step in the presentation of viral antigens to CD8+ T cells. This process is subject to quality control restrictions that prevent free class I heavy chains (HCs) and peptide-free HC-beta(2)-microglobulin (beta(2)m) dimers from exiting the ER. The lectin-like chaperone calreticulin associates with HC-beta(2)m heterodimers prior to peptide binding, but its precise role in regulating the subsequent events of peptide association and ER to Golgi transport remains undefined. In vitro analysis of the assembly process has been limited by the specificity of calreticulin for monoglucosylated N-linked glycans, which are transient biosynthetic intermediates. To address this problem, we developed a novel expression system using Saccharomyces cerevisiae glycosylation mutants to produce class I HC bearing N-linked oligosaccharides with the specific structure Glc(1)Man(9)GlcNAc(2). The monoglucosylated glycan proved to be both necessary and sufficient for in vitro binding of calreticulin to MHC class I molecules. Calreticulin bound as efficiently to peptide-loaded MHC class I complexes as it did to folding intermediates created in vitro, namely free class I HC and empty HC-beta(2)m heterodimers. Thus, calreticulin is unable to discriminate between native and non-native MHC class I conformations and therefore unlikely to play a role in the recognition and release of peptide-loaded complexes from the ER. Furthermore, the recombinant expression system developed in this study can be used to produce a broad range of calreticulin substrates to elucidate its general mechanism of activity in vitro. PMID:15056662

Wearsch, Pamela A; Jakob, Claude A; Vallin, Antonio; Dwek, Raymond A; Rudd, Pauline M; Cresswell, Peter

2004-06-11

86

Inhibition of host cell encapsulation through inhibiting immune gene expression by the parasitic wasp venom calreticulin.  

PubMed

Parasitoid wasps inject venom into the host to protect their offspring against host immune responses. In our previous study, we identified a calreticulin (CRT) in Pteromalus puparum venom. In this study, we expressed the wild-type and the coiled-coil domain deletion mutant P. puparum calreticulins (PpCRTs) in Escherichia coli and prepared polyclonal antibody in rabbit against PpCRT. Western blot analysis showed that PpCRT protein was not only present in the venom but also in all the tissues tested. Real time PCR results indicated that PpCRT mRNA was highly expressed in the venom gland. The transcript level of PpCRT in the venom gland was peaked at 2 days post-eclosion, while the PpCRT protein in the venom was maintained at a constant level. Both recombinant wild-type and mutant PpCRT proteins could bind to the surface of P. puparum eggs. Recombinant PpCRT inhibited hemocyte spreading and cellular encapsulation of the host Pieris rapae in vitro, and the coiled-coil domain is important for the inhibitory function of PpCRT. Immunocytochemistry results showed that PpCRT entered P. rapae hemocytes, and the coiled-coil domain played a role in this process. After injection of recombinant PpCRT into P. rapae pupae, real time PCR results showed that PpCRT inhibited transcript levels of host encapsulation-related genes, including calreticulin and scavenger receptor genes. In conclusion, our results suggest that P. puparum venom protects its offspring against host cellular immune responses via its functional component PpCRT to inhibit the expression of host cellular response-related genes. PMID:23933213

Wang, Lei; Fang, Qi; Qian, Cen; Wang, Fei; Yu, Xiao-Qiang; Ye, Gongyin

2013-10-01

87

Roles of Trypanosoma cruzi calreticulin in parasite-host interactions and in tumor growth.  

PubMed

In Latin America, there are about 10-12 million people infected with Trypanosoma cruzi, the agent of Chagas' disease, one of the most important neglected tropical parasitism. Identification of molecular targets, specific for the aggressor or host cells or both, may be useful in the development of pharmacological and/or immunological therapeutic tools. Classic efforts in Chagas' disease explore those strategies. Although the immune system frequently controls parasite aggressions, sterile immunity is seldom achieved and chronic interactions are thus established. However, laboratory-modified immunologic probes aimed at selected parasite targets, may be more effective than their unmodified counterparts. Calreticulin (CRT) from vertebrates is a calcium binding protein, present mainly in the endoplasmic reticulum (ER), where it directs the conformation of proteins and controls calcium levels. We have isolated, gene-cloned, expressed and characterized T. cruzi calreticulin (TcCRT). Upon infection, the parasite can translocate this molecule from the ER to the surface, where it inhibits both the classical and lectin complement pathways. Moreover, by virtue of its capacity to bind and inactivate first complement component C1, it promotes parasite infectivity. These two related properties reside in the central domain of this molecule. A different domain, amino terminal, binds to endothelial cells, thus inhibiting their angiogenic capacity. Since tumor growth depends, to a large extent on angiogenesis, their growth is also inhibited. PMID:22673211

Ramírez, Galia; Valck, Carolina; Aguilar, Lorena; Kemmerling, Ulrike; López-Muñoz, Rodrigo; Cabrera, Gonzalo; Morello, Antonio; Ferreira, Jorge; Maya, Juan Diego; Galanti, Norbel; Ferreira, Arturo

2012-10-01

88

Protein kinase C is involved in the regulation of several calreticulin posttranslational modifications.  

PubMed

Calreticulin (CRT) is a highly versatile lectin-like chaperone that affects many cellular functions both inside and outside the endoplasmic reticulum lumen. We previously reported that calreticulin interacts with several protein kinase C isozymes both in vitro and in vivo. The aim of this study was to elucidate the molecular determinants involved in the association between these proteins and the biochemical significance of their interaction. Using full-length or CRT-domain constructs expressed as GST-fusion proteins, we found that protein kinase C binds to the CRT N domain in overlay and pull-down assays. Phosphorylation experiments showed that only this CRT domain is phosphorylated by the kinase. Lectin blot analysis demonstrated that CRT is modified by N-glycosylation, but this modification did not affect its interaction with protein kinase C. We also demonstrated that although both domains of protein kinase C theta can bind to CRT, it is the catalytic one that binds with higher affinity to CRT. Immunofluorescence studies showed that CRT and PKC co-localize mainly at the ER (estimated in 35%). Activation of protein kinase C induced caused transient changes in CRT localization, and unexpectedly, also induced changes in posttranslational modifications found in the protein: CRT N-glycosylation is abolished, whereas tyrosine phosphorylation and O-linked beta-N-acetylglucosamine modification are increased. Together, these findings suggest that protein kinase C is involved in the regulation of CRT function. PMID:19800981

Cristina Castañeda-Patlán, M; Razo-Paredes, Roberto; Carrisoza-Gaytán, Rolando; González-Mariscal, Lorenza; Robles-Flores, Martha

2010-01-01

89

Sindbis virus replicon particles encoding calreticulin linked to a tumor antigen generate long-term tumor-specific immunity  

Microsoft Academic Search

Alphavirus vectors have emerged as a promising strategy for the development of cancer vaccines and gene therapy applications. In this study, we used the replication-defective vaccine vector SIN replicon particles from a new packaging cell line (PCL) to develop SIN replicon particles encoding calreticulin (CRT) linked to a model tumor antigen, human papillomavirus type 16 (HPV16) E7 protein. The linkage

W-F Cheng; C-N Lee; Y-N Su; C-Y Chai; M-C Chang; J M Polo; C-F Hung; T-C Wu; C-Y Hsieh; C-A Chen

2006-01-01

90

Calreticulin, a Molecular Chaperone in the Endoplasmic Reticulum, Modulates Radiosensitivity of Human Glioblastoma U251MG Cells  

Microsoft Academic Search

Radiotherapy is the primary and most important adjuvant therapy for malignant gliomas. Although the mechanism of radiation resistance in gliomas has been studied for decades, it is still not clear how the resistance is related with functions of molecular chaperones in the endoplasmic reticulum. Calreticulin (CRT) is a Ca2+-binding molecular chaperone in the endoplasmic reticulum. Recently, it was reported that

Tomohiro Okunaga; Yoshishige Urat; Shinji Goto; Takayuki Matsuo; Shingo Mizota; Keisuke Tsutsumi; Izumi Nagata; Takahito Kondo; Yoshito Ihara

2006-01-01

91

Calreticulin exposure on malignant blasts predicts a cellular anticancer immune response in patients with acute myeloid leukemia  

Microsoft Academic Search

Experiments performed in mice revealed that anthracyclines stimulate immunogenic cell death that is characterized by the pre-apoptotic exposure of calreticulin (CRT) on the surface of dying tumor cells. Here, we determined whether CRT exposure at the cell surface (ecto-CRT) occurs in human cancer in response to anthracyclines in vivo, focusing on acute myeloid leukemia (AML), which is currently treated with

M Wemeau; O Kepp; A Tesnière; T Panaretakis; C Flament; S De Botton; L Zitvogel; G Kroemer; N Chaput

2010-01-01

92

Calreticulin, a Peptide-binding Chaperone of the Endoplasmic Reticulum, Elicits Tumor and Peptide-specific Immunity  

Microsoft Academic Search

Summary Calreticulin (CRT), a peptide-binding heat shock protein (HSP) of the endoplasmic reticulum (ER), has been shown previously to associate with peptides transported into the ER by trans- porter associated with antigen processing (Spee, P., and J. Neefjes. 1997. Eur. J. Immunol. 27: 2441-2449). Our studies show that CRT preparations purified from tumors elicit specific im- munity to the tumor

Sreyashi Basu; Pramod K. Srivastava

93

Assessment of roles for calreticulin in the cross-presentation of soluble and bead-associated antigens.  

PubMed

Antigen cross-presentation involves the uptake and processing of exogenously derived antigens and their assembly with major histocompatibility complex (MHC) class I molecules. Antigen presenting cells (APC) load peptides derived from the exogenous antigens onto MHC class I molecules for presentation to CD8 T cells. Calreticulin has been suggested to mediate and enhance antigen cross-presentation of soluble and cell-derived antigens. In this study, we examined roles for calreticulin in cross-presentation of ovalbumin using a number of models. Our findings indicate that calreticulin does not enhance in vitro cross-presentation of an ovalbumin-derived peptide, or of fused or bead-associated ovalbumin. Additionally, in vivo, calreticulin fusion or co-conjugation does not enhance the efficiency of CD8 T cell activation by soluble or bead-associated ovalbumin either in wild type mice or in mice lacking Toll-like receptor 4 (TLR4). Furthermore, we detect no significant differences in cross-presentation efficiencies of glycosylated vs. non-glycosylated forms of ovalbumin. Together, these results point to the redundancies in pathways for uptake of soluble and bead-associated antigens. PMID:22848581

Del Cid, Natasha; Shen, Lianjun; Belleisle, Janice; Raghavan, Malini

2012-01-01

94

Calreticulin-STAT3 Signaling Pathway Modulates Mitochondrial Function in a Rat Model of Furazolidone-Induced Dilated Cardiomyopathy  

PubMed Central

Background Calreticulin is a Ca2+-binding chaperone of the endoplasmic reticulum which regulates the signal transducer and activator of transcription 3 (STAT3). The effects of the calreticulin-STAT3 signaling pathway on cardiac mitochondria and on the progress of dilated cardiomyopathy (DCM) are still unclear. Methods and Results The DCM model was generated in rats by the daily oral administration of furazolidone. Echocardiographic and hemodynamic studies demonstrated enlarged LV dimensions and reduced systolic and diastolic functions at thirty weeks after the first furazolidone administration. Morphometric analysis showed significant myocardial degeneration, interstitial fibrosis, and mitochondrial swelling with fractured or dissolved cristae in the model group. Compared with the control group, the mitochondrial membrane potential (MMP) level of the freshly isolated cardiac mitochondria and the enzyme activities of cytochrome c oxidase and succinate dehydrogenase in the model group were significantly decreased (P<0.05). Real-time PCR and western-blot revealed the increased expression of calreticulin associated with decreased activity of STAT3 in the model group. When cultured neonatal rat cardiomyocytes were exposed to furazolidone, a dose-dependent decrease in cell viability and MMP, and the increase of apoptosis rate were observed. The mRNA and protein expression of CRT gradually increased with the increase of furazolidone concentration, associated with a gradual decrease of the STAT3 phosphorylation level both in the whole cell and mitochondrial fraction. When calreticulin was knocked down with siRNA in cardiomyocytes, these changes of cardiomyocytes and mitochondria induced by furazolidone were significantly attenuated. Conclusions A rat model of DCM induced by furazolidone is successfully established. The calreticulin-STAT3 signaling pathway is involved in cardiac mitochondrial injury and the progress of furazolidone induced DCM. PMID:23818963

Zhang, Ming; Wei, Jin; Shan, Hu; Wang, Hao; Zhu, Yanhe; Xue, Jiahong; Lin, Lin; Yan, Rui

2013-01-01

95

Hijacking of host calreticulin is required for the white spot syndrome virus replication cycle.  

PubMed

We have previously shown that multifunctional calreticulin (CRT), which resides in the endoplasmic reticulum (ER) and is involved in ER-associated protein processing, responds to infection with white spot syndrome virus (WSSV) by increasing mRNA and protein expression and by forming a complex with gC1qR and thereby delaying apoptosis. Here, we show that CRT can directly interact with WSSV structural proteins, including VP15 and VP28, during an early stage of virus infection. The binding of VP28 with CRT does not promote WSSV entry, and CRT-VP15 interaction was detected in the viral genome in virally infected host cells and thus may have an effect on WSSV replication. Moreover, CRT was detected in the viral envelope of purified WSSV virions. CRT was also found to be of high importance for proper oligomerization of the viral structural proteins VP26 and VP28, and when CRT glycosylation was blocked with tunicamycin, a significant decrease in both viral replication and assembly was detected. Together, these findings suggest that CRT confers several advantages to WSSV, from the initial steps of WSSV infection to the assembly of virions. Therefore, CRT is required as a "vital factor" and is hijacked by WSSV for its replication cycle. Importance: White spot syndrome virus (WSSV) is a double-stranded DNA virus and the cause of a serious disease in a wide range of crustaceans that often leads to high mortality rates. We have previously shown that the protein calreticulin (CRT), which resides in the endoplasmic reticulum (ER) of the cell, is important in the host response to the virus. In this report, we show that the virus uses this host protein to enter the cell and to make the host produce new viral structural proteins. Through its interaction with two viral proteins, the virus "hijacks" host calreticulin and uses it for its own needs. These findings provide new insight into the interaction between a large DNA virus and the host protein CRT and may help in understanding the viral infection process in general. PMID:24807724

Watthanasurorot, Apiruck; Guo, Enen; Tharntada, Sirinit; Lo, Chu-Fang; Söderhäll, Kenneth; Söderhäll, Irene

2014-07-01

96

Folding of thyroglobulin in the calnexin/calreticulin pathway and its alteration by loss of Ca2+ from the endoplasmic reticulum.  

PubMed Central

During its initial folding in the endoplasmic reticulum (ER), newly synthesized thyroglobulin (Tg) is known to interact with calnexin and other ER molecular chaperones, but its interaction with calreticulin has not been examined previously. In the present study, we have investigated the interactions of endogenous Tg with calreticulin and with several other ER chaperones. We find that, in FRTL-5 and PC-Cl3 cells, calnexin and calreticulin interact with newly synthesized Tg in a carbohydrate-dependent manner, with largely overlapping kinetics that are concomitant with the maturation of Tg intrachain disulphide bonds, preceding Tg dimerization and exit from the ER. Calreticulin co-precipitates more newly synthesized Tg than does calnexin; however, using two different experimental approaches, calnexin and calreticulin were found in ternary complexes with Tg, making this the first endogenous protein reported in ternary complexes with calnexin and calreticulin in the ER of live cells. Depletion of Ca(2+) from the ER elicited by thapsigargin (a specific inhibitor of ER Ca(2+)-ATPases) results in retention of Tg in this organelle. Interestingly, thapsigargin treatment induces the premature exit of Tg from the calnexin/calreticulin cycle, while stabilizing and prolonging interactions of Tg with BiP (immunoglobulin heavy chain binding protein) and GRP94 (glucose-regulated protein 94), two chaperones whose binding is not carbohydrate-dependent. Our results suggest that calnexin and calreticulin, acting in ternary complexes with a large glycoprotein substrate such as Tg, might be engaged in the folding of distinct domains, and indicate that lumenal Ca(2+) strongly influences the folding of exportable glycoproteins, in part by regulating the balance of substrate binding to different molecular chaperone systems within the ER. PMID:12401114

Di Jeso, Bruno; Ulianich, Luca; Pacifico, Francesco; Leonardi, Antonio; Vito, Pasquale; Consiglio, Eduardo; Formisano, Silvestro; Arvan, Peter

2003-01-01

97

From Janus kinase 2 to calreticulin: the clinically relevant genomic landscape of myeloproliferative neoplasms.  

PubMed

Our understanding of the genetic basis of myeloproliferative neoplasms began in 2005, when the JAK2 (V617F) mutation was identified in polycythemia vera, essential thrombocythemia, and primary myelofibrosis. JAK2 exon 12 and MPL exon 10 mutations were then detected in subsets of patients, and subclonal driver mutations in other genes were found to be associated with disease progression. Recently, somatic mutations in the gene CALR, encoding calreticulin, have been found in most patients with essential thrombocythemia or primary myelofibrosis with nonmutated JAK2 and MPL. The JAK-STAT pathway appears to be activated in all myeloproliferative neoplasms, regardless of founding driver mutations. These latter, however, have different effects on clinical course and outcomes. Thus, evaluation of JAK2, MPL, and CALR mutation status is important not only for diagnosis but also for prognostication. These genetic data should now also be considered in designing clinical trials. PMID:24786775

Cazzola, Mario; Kralovics, Robert

2014-06-12

98

The function of calreticulin in plant immunity: new discoveries for an old protein.  

PubMed

Since its initial discovery as a high affinity Ca ( 2+) -binding protein in the sarcoplasmic reticulum and endoplasmic reticulum (ER), calreticulin (CRT) has been documented to be a multifunctional protein in both animal and plant cells. This protein is well recognized as a Ca ( 2+) -binding molecular chaperone that facilitates the folding of newly synthesized glycoproteins and regulates the Ca ( 2+) homeostasis in the ER lumen. However, functional relevance associated with its localization in other cellular compartments has also been reported. Recent studies suggest that both isoforms of plant CRTs (AtCRT1/2 and AtCRT3) are involved in regulating plant defense against biotrophic pathogens. Here we discuss the cellular functions of CRT and its connection to the emerging functions of AtCRTs in plant immunity. PMID:22827946

Qiu, Yongjian; Xi, Jing; Du, Liqun; Poovaiah, B W

2012-08-01

99

Molecular cloning and functional study of calreticulin from a lepidopteran pest, Pieris rapae.  

PubMed

Insects have an effective innate immune system to protect themselves from exogenous invaders. Calreticulin is a multifunctional protein mainly involved in directing proper conformation of proteins, controlling calcium level, and participating in immune responses. Previous suppression subtractive hybridization assay showed that the expression of Pieris rapae calreticulin (PrCRT) was suppressed after injection of Pteromalus puparum venom. In this study, we obtained a full length cDNA of PrCRT and expressed recombinant wild type and the N-domain deleted mutant PrCRT in bacteria. Real time quantitative PCR and western blot analyses showed that PrCRT mRNA and protein were expressed in hemocytes, Malpighian tubule, midgut, epidermis and fat body, with a higher level in hemocytes. PrCRT was probably located in endoplasmic reticulum distributing in the cytoplasm of hemocytes. Recombinant PrCRT was first able to attach and then enter the hemocytes by endocytosis. PrCRT mRNA in hemocytes was significantly induced after injection of yeast or beads, but did not change noticeably after injection of Escherichia coli or Micrococcus lysodeikticus. Recombinant PrCRT enhanced cellular encapsulation by P. rapae hemocytes in vitro, and the N-domain of PrCRT was required for encapsulation. RNAi of PrCRT by dsRNA injection impaired the ability of hemocytes to encapsulate beads. After parasitization by P. puparum, PrCRT mRNA and protein levels in P. rapae pupal hemocytes were significantly suppressed compared to non-parasitized control. Our results suggest that PrCRT is involved in cellular encapsulation and the pupal parasitoid P. puparum can decrease PrCRT expression to impair host cellular immune response. PMID:22516748

Wang, Lei; Fang, Qi; Zhu, Jiaying; Wang, Fei; Rean Akhtar, Zunnu; Ye, Gongyin

2012-09-01

100

Calreticulin, a Calcium-binding Molecular Chaperone, Is Required for Stress Response and Fertility in Caenorhabditis elegans  

PubMed Central

Calreticulin (CRT), a Ca2+-binding protein known to have many cellular functions, including regulation of Ca2+ homoeostasis and chaperone activity, is essential for heart and brain development during embryogenesis in mice. Here, we report the functional characterization of Caenorhabditis elegans calreticulin (crt-1). A crt-1 null mutant does not result in embryonic lethality but shows temperature-dependent reproduction defects. In C. elegans CRT-1 is expressed in the intestine, pharynx, body-wall muscles, head neurons, coelomocytes, and in sperm. crt-1 males exhibit reduced mating efficiency and defects late in sperm development in addition to defects in oocyte development and/or somatic gonad function in hermaphrodites. Furthermore, crt-1 and itr-1 (inositol triphosphate receptor) together are required for normal behavioral rhythms. crt-1 transcript level is elevated under stress conditions, suggesting that CRT-1 may be important for stress-induced chaperoning function in C. elegans. PMID:11553721

Park, Byung-Jae; Lee, Duk-Gyu; Yu, Jae-Ran; Jung, Sun-ki; Choi, Kyuyeong; Lee, Jungsoo; Lee, Jiyeon; Kim, Yun Sik; Lee, Jin Il; Kwon, Jae Young; Lee, Junho; Singson, Andrew; Song, Woo Keun; Eom, Soo Hyun; Park, Chul-Seung; Kim, Do Han; Bandyopadhyay, Jaya; Ahnn, Joohong

2001-01-01

101

Enhancement of Antibody Responses to Bacillus anthracis Protective Antigen Domain IV by Use of Calreticulin as a Chimeric Molecular Adjuvant  

Microsoft Academic Search

The generation of protective humoral immune responses against the receptor-binding domain (domain IV) of protective antigen (PA(dIV)) of Bacillus anthracis represents a plausible approach against anthrax toxin. In the current study, we have developed a naked DNA vaccine encoding calreticulin (CRT) linked to PA(dIV) of Bacillus anthracis (CRT\\/PA(dIV)). We transfected a human embryonic kidney cell line (HEK 293) with CRT\\/PA(dIV)

Yong Sung Park; Jin Hyup Lee; Chien-Fu Hung; T.-C. Wu; Tae Woo Kim

2008-01-01

102

Transient Association of Calnexin and Calreticulin with Newly Synthesized G1 and G2 Glycoproteins of Uukuniemi Virus (Family Bunyaviridae)  

Microsoft Academic Search

The membrane glycoproteins G1 and G2 of Uukuniemi virus, a member of the Bunyaviridae family, are co- translationally cleaved from a common precursor in the endoplasmic reticulum (ER). Here, we show that newly made G1 and G2 associate transiently with calnexin and calreticulin, two lectins involved in glycoprotein fold- ing in the ER. Stable complexes between G1-G2 and calnexin or

JOHANNA VEIJOLA; RALF F. PETTERSSON

1999-01-01

103

Characterization of DNA vaccines encoding the domains of calreticulin for their ability to elicit tumor-specific immunity and antiangiogenesis  

Microsoft Academic Search

Antigen-specific cancer immunotherapy and antiangiogenesis are feasible strategies for cancer therapy because they can potentially treat systemic tumors at multiple sites in the body while discriminating between neoplastic and non-neoplastic cells. We have previously developed a DNA vaccine encoding calreticulin (CRT) linked to human papillomavirus-16 E7 and have found that this vaccine generates strong E7-specific antitumor immunity and antiangiogenic effects

Wen-Fang Cheng; Chien-Fu Hung; Chi-An Chen; Chien-Nan Lee; Yi-Ning Su; Chee-Yin Chai; David A. K. Boyd; Chang-Yao Hsieh; T.-C. Wu

2005-01-01

104

Calreticulin Is Directly Involved in Anti-?3 Integrin Antibody-Mediated Secretion and Activation of Matrix Metalloprotease-2  

Microsoft Academic Search

Matrix metalloprotease-2 (MMP-2) plays a pivotal role in cancer invasion and metastasis. Invasive human rhabdomyosarcoma cells (RD) secrete proMMP-2. We recently reported that anti-?3 integrin antibody induced the activated form of MMP-2 and enhanced proMMP-2 secretion by RD cells with concomitant enhancement of RD cell invasion. Since recent studies showed that calreticulin interacts with integrin ? subunit, we hypothesized that

Hiromichi Ito; Yousuke Seyama; Shunichiro Kubota

2001-01-01

105

Calreticulin-2 is localized in the lumen of the endoplasmic reticulum but is not a Ca 2+ -binding protein  

Microsoft Academic Search

Calreticulin (CRT)-1 is a major Ca2+-buffering protein in the lumen of the endoplasmic reticulum. Human and murine CRT-2 was isolated in 2002, but the subcellular\\u000a localization and function is still unclear. Here, we studied the intracellular localization and function of CRT-2 with hemagglutinin-tagged\\u000a (HA-) human CRT-2. Western blotting revealed HA-CRT-2 as a single band at 50 kDa. Using immunofluorescence microscopy of

Ryuji Nomura; Minami Orii; Takao Senda

2011-01-01

106

Time Course of SERCA 2b and Calreticulin Expression in Purkinje Neurons of Ethanol-Fed Rats with Behavioral Correlates  

PubMed Central

Chronic ethanol consumption for 40 weeks in adult rats results in dilation of the extensive smooth endoplasmic reticulum (SER), a major component of the calcium homeostatic system within Purkinje neuron (PN) dendrites. Aims: The aim of the present study was to determine whether chronic ethanol consumption results in alterations of the sarco/endoplasmic reticulum Ca2+ ATPase pump (SERCA) on the SER membrane of PN dendrites. The density of calreticulin, a calcium chaperone, was also investigated in the PN along with balancing ability. Methods: Ninety 8-month-old rats were exposed to rat chow, the AIN-93 M liquid control or ethanol diets (30/diet) for a duration of 10, 20 or 40 weeks (30/duration). Age changes relative to the rat chow controls were assessed with 3-month-old control rats (n = 10). Balance was assessed prior to euthanasia. Quantitative immunocytochemistry was used to determine the density of SERCA 2b + dendrites and calreticulin + PN soma and nuclei. Molecular layer volumes were also determined. Results: Following 40 weeks of ethanol treatment, there were ethanol-induced decreases in SERCA 2b densities within the dendritic arbor and decreased balancing ability on the more difficult round rod balance test. There were no ethanol-induced changes in calreticulin densities. Conclusion: It can be concluded that ethanol-induced decreases in the SERCA pump accompany SER dilation and contribute to previously reported ethanol-induced dendritic regression in PN. Ethanol-induced changes in balance also occurred. Chronic ethanol consumption does not alter calreticulin expression in PN. PMID:23884168

Cassidy, Linda L.; Dlugos, Frederick F.; Dlugos, Cynthia A.

2013-01-01

107

Identification of common epitopes on gliadin, enterocytes, and calreticulin recognised by antigliadin antibodies of patients with coeliac disease  

PubMed Central

Background—Sera of patients with coeliac disease, containing IgA and IgG antigliadin antibodies (AGA) and various IgA autoantibodies, react with isolated enterocytes. AGA cross react with enterocyte antigens, one of which has been identified as calreticulin. ?Aims—To characterise the antigenic structures of gliadin, enterocytes, and calreticulin recognised by AGA from patients with active coeliac disease. ?Methods—AGA were isolated from sera of nine patients by affinity chromatography and tested by competitive ELISA using 40 ?-gliadin synthetic dodecapeptides (A1-F6). ?Results—Reactivity of gliadin with all purified AGA tested was inhibited by peptide A4 at the N-terminal region; by C2, C3, and D4 at the central region; and by F3 and F4 at the C-terminal region of the gliadin molecule. AGA cross reactivity with enterocytes was inhibited by peptides A4, D1-D4, and F6 and with calreticulin by peptides A4, D3, and D4. As dominant epitopes AGA of coeliac patients recognise similar structures corresponding to peptides A4, D3, D4, and F6 present on gliadin, enterocytes, and calreticulin. Substitution of glutamine in the A4 peptide by glutamic acid caused loss of inhibitory capacity. Shortening of peptide A4 on the N-terminal by three amino acids increased its inhibitory effect.?Conclusions—AGA of patients with coeliac disease react with similar structures on gliadin and potential autoantigens on enterocytes. ?? Keywords: coeliac disease; antigliadin antibodies; enterocyte autoantigens; cross reactivity PMID:9895374

Krupickova, S; Tuckova, L; Flegelova, Z; Michalak, M; Walters, J; Whelan, A; Harries, J; Vencovsky, J; Tlaskalova-Hogeno..., H

1999-01-01

108

Calreticulin contributes to C1q-dependent recruitment of microglia in the leech Hirudo medicinalis following a CNS injury  

PubMed Central

Background The medicinal leech is considered as a complementary and appropriate model to study immune functions in the central nervous system (CNS). In a context in which an injured leech’s CNS can naturally restore normal synaptic connections, the accumulation of microglia (immune cells of the CNS that are exclusively resident in leeches) has been shown to be essential at the lesion to engage the axonal sprouting. HmC1q (Hm for Hirudo medicinalis) possesses chemotactic properties that are important in the microglial cell recruitment by recognizing at least a C1q binding protein (HmC1qBP alias gC1qR). Material/Methods Recombinant forms of C1q were used in affinity purification and in vitro chemotaxis assays. Anti-calreticulin antibodies were used to neutralize C1q-mediated chemotaxis and locate the production of calreticulin in leech CNS. Results A newly characterized leech calreticulin (HmCalR) has been shown to interact with C1q and participate to the HmC1q-dependent microglia accumulation. HmCalR, which has been detected in only some microglial cells, is consequently a second binding protein for HmC1q, allowing the chemoattraction of resident microglia in the nerve repair process. Conclusions These data give new insight into calreticulin/C1q interaction in an immune function of neuroprotection, suggesting another molecular target to use in investigation of microglia reactivity in a model of CNS injury. PMID:24747831

Le Marrec-Croq, Francoise; Bocquet-Garcon, Annelise; Vizioli, Jacopo; Vancamp, Christelle; Drago, Francesco; Franck, Julien; Wisztorski, Maxence; Salzet, Michel; Sautiere, Pierre-Eric; Lefebvre, Christophe

2014-01-01

109

Expression of the high capacity calcium-binding domain of calreticulin increases bioavailable calcium stores in plants  

NASA Technical Reports Server (NTRS)

Modulation of cytosolic calcium levels in both plants and animals is achieved by a system of Ca2+-transport and storage pathways that include Ca2+ buffering proteins in the lumen of intracellular compartments. To date, most research has focused on the role of transporters in regulating cytosolic calcium. We used a reverse genetics approach to modulate calcium stores in the lumen of the endoplasmic reticulum. Our goals were two-fold: to use the low affinity, high capacity Ca2+ binding characteristics of the C-domain of calreticulin to selectively increase Ca2+ storage in the endoplasmic reticulum, and to determine if those alterations affected plant physiological responses to stress. The C-domain of calreticulin is a highly acidic region that binds 20-50 moles of Ca2+ per mole of protein and has been shown to be the major site of Ca2+ storage within the endoplasmic reticulum of plant cells. A 377-bp fragment encoding the C-domain and ER retention signal from the maize calreticulin gene was fused to a gene for the green fluorescent protein and expressed in Arabidopsis under the control of a heat shock promoter. Following induction on normal medium, the C-domain transformants showed delayed loss of chlorophyll after transfer to calcium depleted medium when compared to seedlings transformed with green fluorescent protein alone. Total calcium measurements showed a 9-35% increase for induced C-domain transformants compared to controls. The data suggest that ectopic expression of the calreticulin C-domain increases Ca2+ stores, and that this Ca2+ reserve can be used by the plant in times of stress.

Wyatt, Sarah E.; Tsou, Pei-Lan; Robertson, Dominique; Brown, C. S. (Principal Investigator)

2002-01-01

110

Occurrence of IgA and IgG Autoantibodies to Calreticulin in Coeliac Disease and Various Autoimmune Diseases  

Microsoft Academic Search

Calreticulin (CRT), a high-affintiy calcium binding protein and chaperone, was recently identified as one of the targets of autoantibodies in coeliac disease. We evaluated the level of IgA and IgG antibodies to CRT in sera from patients with coeliac disease and various autoimmune diseases. The level of antibodies to gliadin (shown previously to cross-react with CTR), isolated enterocytes and tissue

D Sánchez; L Tu?ková; P Šebo; M Michalak; A Whelan; I Šterzl; L Jel??nková; E Havrdová; M Imramovská; Z Beneš; S Krupi?ková; H Tlaskalová-Hogenová

2000-01-01

111

Anti-gliadin Antibodies in Patients with Celiac Disease Cross-react with Enterocytes and Human Calreticulin  

Microsoft Academic Search

One of the characteristic features of celiac disease is an increase in anti-gliadin antibodies (Abs). Recently we found that some of the monoclonal Abs to gliadin cross-react with molecules on rat enterocytes. One of these cross-reacting molecules was identified as rat calreticulin. This study shows that the levels of serum IgA Abs to gliadin, rat, and human enterocytes; purified enterocyte

Ludmila Tu?ková; Kamila Karská; Julian R. F. Walters; Marek Michalak; Pavel Rossmann; Stanislava Krupi?ková; Elena F. Verdu; Robert Saalman; Lars A. Hanson; Helena Tlaskalová-Hogenová

1997-01-01

112

Trypanosoma cruzi calreticulin: A novel virulence factor that binds complement C1 on the parasite surface and promotes infectivity  

Microsoft Academic Search

In Trypanosoma cruzi, calreticulin (TcCRT) translocates from the endoplasmic reticulum (ER) to the area of flagellum emergence. We propose herein that the parasite uses this molecule to capture complement C1, in an infective apoptotic mimicry strategy. Thus, TcCRT\\/C1 interactions, besides inhibiting the classical pathway of complement activation as previously shown in our laboratories, will also promote infectivity. This fact correlates

Galia Ramírez; Carolina Valck; María C. Molina; Carolina H. Ribeiro; Nandy López; Gittith Sánchez; Viviana P. Ferreira; Rosario Billetta; Lorena Aguilar; Ismael Maldonado; Pedro Cattán; Wilhelm Schwaeble; Arturo Ferreira

2010-01-01

113

Molecular mechanisms involved in the inactivation of the first component of human complement by Trypanosoma cruzi calreticulin  

Microsoft Academic Search

Trypanosoma cruzi (T. cruzi), the agent of Chagas’ disease, the sixth most important neglected tropical disease worldwide, causes 50,000 deaths per year in Latin America. T. cruzi calreticulin (TcCRT), a highly pleiotropic chaperone molecule, plays important roles in several host\\/parasite interactions. Among other functions, we have previously shown that TcCRT, translocated from the endoplasmic reticulum to the area of flagellar

Carolina Valck; Galia Ramírez; Nandy López; Carolina H. Ribeiro; Ismael Maldonado; Gittith Sánchez; Viviana P. Ferreira; Wilhelm Schwaeble; Arturo Ferreira

2010-01-01

114

Assessment of Roles for Calreticulin in the Cross-Presentation of Soluble and Bead-Associated Antigens  

Microsoft Academic Search

Antigen cross-presentation involves the uptake and processing of exogenously derived antigens and their assembly with major histocompatibility complex (MHC) class I molecules. Antigen presenting cells (APC) load peptides derived from the exogenous antigens onto MHC class I molecules for presentation to CD8 T cells. Calreticulin has been suggested to mediate and enhance antigen cross-presentation of soluble and cell-derived antigens. In

Natasha Del Cid; Lianjun Shen; Janice BelleIsle; Malini Raghavan

2012-01-01

115

Sumoylation regulates ER stress response by modulating calreticulin gene expression in XBP-1-dependent mode in Caenorhabditis elegans.  

PubMed

Excessive accumulation of unfolded proteins in the endoplasmic reticulum (ER) lumen causes ER stress, which induces a set of genes, including those encoding ER-resident chaperones, to relieve the detrimental effects and recover homeostasis. Calreticulin is a chaperone that facilitates protein folding in the ER lumen, and its gene expression is induced by ER stress in Caenorhabditis elegans. Sumoylation conjugates small ubiquitin-like modifier (SUMO) proteins with target proteins to regulate a variety of biological processes, such as protein stability, nuclear transport, DNA binding, and gene expression. In this study, we showed that C. elegans X-box-binding protein 1 (Ce-XBP-1), an ER stress response transcription factor, interacts with the SUMO-conjugating enzyme UBC-9 and a SUMOylation target. Our results indicated that abolishing sumoylation enhanced calreticulin expression in an XBP-1-dependent manner, and the resulting increase in calreticulin counteracted ER stress. Furthermore, sumoylation was repressed in C. elegans undergoing ER stress. Finally, RNAi against ubc-9 mainly affected the expression of genes associated with ER functions, such as lipid and organic acid metabolism. Our results suggest that sumoylation plays a regulatory role in ER function by controlling the expression of genes required for ER homeostasis in C. elegans. PMID:24933177

Lim, Yunki; Lee, Dukgyu; Kalichamy, Karunambigai; Hong, Seong-Eui; Michalak, Marek; Ahnn, Joohong; Kim, Do Han; Lee, Sun-Kyung

2014-08-01

116

Catalyzed gasification of biomass  

Microsoft Academic Search

Catalyzed biomass gasification studies are being conducted by Battelle's Pacific Northwest Laboratories. Investigations are being carried out concurrently at the bench and process development unit scales. These studies are designed to test the technical and economic feasibility of producing specific gaseous products from biomass by enhancing its reactivity and product specificity through the use of specific catalysts. The program is

L. J. Jr. Sealock; R. J. Robertus; L. K. Mudge; D. H. Mitchell; J. L. Cox

1978-01-01

117

Trypanosoma cruzi calreticulin inhibits the complement lectin pathway activation by direct interaction with L-Ficolin.  

PubMed

Trypanosoma cruzi, the agent of Chagas' disease, the sixth neglected tropical disease worldwide, infects 10-12 million people in Latin America. Differently from T. cruzi epimastigotes, trypomastigotes are complement-resistant and infective. CRPs, T-DAF, sialic acid and lipases explain at least part of this resistance. In vitro, T. cruzi calreticulin (TcCRT), a chaperone molecule that translocates from the ER to the parasite surface: (a) Inhibits the human classical complement activation, by interacting with C1, (b) As a consequence, an increase in infectivity is evident and, (c) It inhibits angiogenesis and tumor growth. We report here that TcCRT also binds to the L-Ficolin collagenous portion, thus inhibiting approximately between 35 and 64% of the human complement lectin pathway activation, initiated by L-Ficolin, a property not shared by H-Ficolin. While L-Ficolin binds to 60% of trypomastigotes and to 24% of epimastigotes, 50% of the former and 4% of the latter display TcCRT on their surfaces. Altogether, these data indicate that TcCRT is a parasite inhibitory receptor for Ficolins. The resulting evasive activities, together with the TcCRT capacity to inhibit C1, with a concomitant increase in infectivity, may represent T. cruzi strategies to inhibit important arms of the innate immune response. PMID:24769495

Sosoniuk, Eduardo; Vallejos, Gerardo; Kenawy, Hany; Gaboriaud, Christine; Thielens, Nicole; Fujita, Teizo; Schwaeble, Wilhelm; Ferreira, Arturo; Valck, Carolina

2014-07-01

118

Self-Oligomerization Is Essential for Enhanced Immunological Activities of Soluble Recombinant Calreticulin  

PubMed Central

We have recently reported that calreticulin (CRT), a luminal resident protein, can be found in the sera of patients with rheumatoid arthritis and also that recombinant CRT (rCRT) exhibits extraordinarily strong immunological activities. We herein further demonstrate that rCRT fragments 18–412 (rCRT/18-412), rCRT/39-272, rCRT/120-308 and rCRT/120-250 can self-oligomerize in solution and are 50–100 fold more potent than native CRT (nCRT, isolated from mouse livers) in activating macrophages in vitro. We narrowed down the active site of CRT to residues 150–230, the activity of which also depends on dimerization. By contrast, rCRT/18-197 is almost completely inactive. When rCRT/18-412 is fractionated into oligomers and monomers by gel filtration, the oligomers maintain most of their immunological activities in terms of activating macrophages in vitro and inducing specific antibodies in vivo, while the monomers were much less active by comparison. Additionally, rCRT/18-412 oligomers are much better than monomers in binding to, and uptake by, macrophages. Inhibition of macrophage endocytosis partially blocks the stimulatory effect of rCRT/18-412. We conclude that the immunologically active site of CRT maps between residues 198–230 and that soluble CRT could acquire potent immuno-pathological activities in microenvironments favoring its oligomerization. PMID:23762269

Huang, Shang-Hui; Zhao, Li-Xiang; Hong, Chao; Duo, Cui-Cui; Guo, Bing-Nan; Zhang, Li-Juan; Gong, Zheng; Xiong, Si-Dong; Gong, Fang-Yuan; Gao, Xiao-Ming

2013-01-01

119

Calnexin and calreticulin promote folding, delay oligomerization and suppress degradation of influenza hemagglutinin in microsomes.  

PubMed Central

Calnexin (CNX) and calreticulin (CRT) are molecular chaperones that bind preferentially to monoglucosylated trimming intermediates of glycoproteins in the endoplasmic reticulum. To determine their role in the maturation of newly synthesized glycoproteins, we analyzed the folding and trimerization of in vitro translated influenza hemagglutinin (HA) in canine pancreas microsomes under conditions in which HA's interactions with CNX and CRT could be manipulated. While CNX bound to all folding intermediates (IT1, IT2 and NT), CRT was found to associate preferentially with the earliest oxidative form (IT1). If HA's binding to CNX and CRT was inhibited using a glucosidase inhibitor, castanospermine (CST), the rate of disulfide formation and oligomerization was doubled but the overall efficiency of maturation of HA decreased due to aggregation and degradation. If, on the other hand, HA was arrested in CNX-CRT complexes, folding and trimerization were inhibited. This suggested that the action of CNX and CRT, like that of other chaperones, depended on an 'on-and-off' cycle. Taken together, these results indicated that CNX and CRT promote correct folding by inhibiting aggregation, preventing premature oxidation and oligomerization, and by suppressing degradation of incompletely folded glycopolypeptides. Images PMID:8670797

Hebert, D N; Foellmer, B; Helenius, A

1996-01-01

120

A sandwich enzyme-linked immunosorbent assay for detection of calreticulin in human serum.  

PubMed

Calreticulin (CRT) is a 46 kDa Ca(2+) binding chaperone protein that is mainly located in the endoplasmic reticulum luminal and has various biological functions. It is important to establish a specific and sensitive CRT enzyme-linked immunosorbent assay (ELISA) for the study of CRT functions. Therefore, we prepared a polyclonal antibody (PAb) in rabbits immunized with a recombinant CRT protein. Based on the PAb and our previously prepared monoclonal antibody (MAb), a highly specific and sensitive ELISA was developed. In the present study, we describe a sandwich ELISA for the determination of CRT protein in human serum. It was found that soluble CRT (sCRT) concentration in serum samples from 49 lung cancer patients was significantly higher than that from 53 healthy individuals (p=0.004). This result demonstrates that sCRT concentration in sera of lung cancer patients is higher than that in sera of healthy individuals. In conclusion, the prepared CRT antibodies and developed ELISA is a potential tool for CRT research and offers an alternative, simple, rapid technique for detecting CRT, especially in large ongoing and future clinical studies. PMID:24111870

Wu, Wei; Wang, Gongze; Tan, Chao; Zou, Xiaohua; Wang, Yanlin; Liu, Chaoqi

2013-10-01

121

Calreticulin is localized at mitochondria of rat cardiomyocytes and affected by furazolidone.  

PubMed

Calreticulin (CRT) is a calcium-buffering protein which is predominantly located in endoplasmic reticulum. In the previous mitochondria proteome analysis, we accidentally found that CRT may be also localized at myocardial mitochondria and was upregulated in a rat model of furazolidone-induced dilated cardiomyopathy. To our knowledge, there has not yet been any report of its presence in mitochondria of any cell types. The present study aimed to determine whether CRT was located at the mitochondria of rat cardiomyocytes and whether the mitochondrial CRT was affected by furazolidone. Mitochondrial preparations were isolated from primary cultured neonatal rat cardiomyocytes and purified by differential centrifugation. The purity of mitochondria was assessed by the reduction or elimination of the immunoreactivities of markers for cytosol, nucleus, sarcolemma, and endoplasmic reticulum. Western blot analysis demonstrated the presence of CRT in purified mitochondria of rat cardiomyocytes. The distribution of CRT to mitochondria was further confirmed by immuno-electron microscopy, flow cytometry, and laser scanning confocal microscopy (double staining with MitoTracker Red and CRT-Alexa Fluor 488). Western blot analysis also demonstrated that the mitochondrial content of CRT was significantly enhanced by furazolidone treatment by 2.73 ± 0.13 fold (P < 0.05) in rat cardiomyocytes, which was verified by immuno-electron microscopy. In summary, the present results suggest that CRT is localized at mitochondria of rat cardiomyocytes and such localization is affected by furazolidone. PMID:25087122

Shan, Hu; Wei, Jin; Zhang, Ming; Lin, Lin; Yan, Rui; Zhu, Yanhe; Zhang, Rong

2014-12-01

122

Endoplasmic Reticulum Calcium Regulates the Retrotranslocation of Trypanosoma Cruzi Calreticulin to the Cytosol  

PubMed Central

For most secretory pathway proteins, crossing the endoplasmic reticulum (ER) membrane is an irreversible process. However, in some cases this flow can be reversed. For instance, misfolded proteins retained in the ER are retrotranslocated to the cytosol to be degraded by the proteasome. This mechanism, known as ER associated degradation (ERAD), is exploited by several bacterial toxins to gain access to the cytosol. Interestingly, some ER resident proteins can also be detected in the cytosol or nucleus, calreticulin (CRT) being the most studied. Here we show that in Trypanosoma cruzi a minor fraction of CRT localized to the cytosol. ER calcium depletion, but not increasing cytosolic calcium, triggered the retrotranslocation of CRT in a relatively short period of time. Cytosolic CRT was subsequently degraded by the proteasome. Interestingly, the single disulfide bridge of CRT is reduced when the protein is located in the cytosol. The effect exerted by ER calcium was strictly dependent on the C-terminal domain (CRT-C), since a CRT lacking it was totally retained in the ER, whereas the localization of an unrelated protein fused to CRT-C mirrored that of endogenous CRT. This finding expands the regulatory mechanisms of protein sorting and may represent a new crossroad between diverse physiological processes. PMID:20957192

Labriola, Carlos A.; Conte, Ianina L.; López Medus, Máximo; Parodi, Armando J.; Caramelo, Julio J.

2010-01-01

123

Impact of calreticulin mutations on clinical and hematological phenotype and outcome in essential thrombocythemia.  

PubMed

Mutations in the calreticulin (CALR) gene were recently discovered in patients with essential thrombocythemia (ET) lacking the JAK2V617F and MPLW515 mutations, but no information is available on the clinical correlates. In this series, CALR mutations were found in 15.5% of 576 World Health Organization-defined ET patients, accounting for 48.9% of JAK2 and MPL wild-type (wt) patients. CALR-mutated patients were preferentially male and showed higher platelet count and lower hemoglobin and leukocyte count compared with JAK2- and MPL-mutated patients. Patients carrying the CALR mutation had a lower risk of thrombosis than JAK2- and MPL-mutated patients; of interest, their risk was superimposable to patients who were wt for the above mutations. CALR mutation had no impact on survival or transformation to post-ET myelofibrosis. Genotyping for CALR mutations represents a novel useful tool for establishing a clonal myeloproliferative disorder in JAK2 and MPL wt patients with thrombocytosis and may have prognostic and therapeutic relevance. PMID:24371211

Rotunno, Giada; Mannarelli, Carmela; Guglielmelli, Paola; Pacilli, Annalisa; Pancrazzi, Alessandro; Pieri, Lisa; Fanelli, Tiziana; Bosi, Alberto; Vannucchi, Alessandro M

2014-03-01

124

Loss of calreticulin function decreases NF?B activity by stabilizing I?B protein.  

PubMed

Transcription factor NF?B is activated by several processes including inflammation, endoplasmic-reticulum (ER) stress, increase in Akt signaling and enhanced proteasomal degradation. Calreticulin (CRT) is an ER Ca(2+)-binding chaperone that regulates many cellular processes. Gene-targeted deletion of CRT has been shown to induce ER stress that is accompanied with a significant increase in the proteasome activity. Loss of CRT function increases the resistance of CRT-deficient (crt-/-) cells to UV- and drug-induced apoptosis. Based on these reports we hypothesized that loss of CRT will activate NF?B signaling thus contributing to enhanced resistance to apoptosis. In contrast to our hypothesis, we observed a significant decrease in the basal transcriptional activity of NF?B in CRT-deficient cells. Treatment with lipopolysaccharide failed to increase the transcriptional activity of NF?B in the crt-/- cells to the same level as in the wt cells. Our data illustrate that the mechanism of decreased NF?B activity in CRT-deficient cells is mediated by a significant increase in I?B protein expression. Furthermore, we showed a significant increase in protein phosphatase 2A activity inhibition which resulted in decreased I?B? protein level in CRT-deficient cells. Based on our data we concluded that loss of CRT increases the stability of I?B protein thus reducing NF?B activity. PMID:24998604

Massaeli, Hamid; Jalali, Shahrzad; Viswanathan, Divya; Mesaeli, Nasrin

2014-11-01

125

Purification and characterization of calreticulin: a ca(2+)-binding chaperone from sheep kidney.  

PubMed

Calreticulin (CRT) is a molecular chaperone with a molecular mass of 46 kDa present in the endoplasmic reticulum (ER). This protein is primarily involved in the regulation of intracellular Ca(2+) homeostasis and Ca(2+) storage in the ER. CRT also plays a significant role in autoimmunity and cancer. This protein contains three distinct structural domains with specialized functions. Here, we are reporting a simple procedure for the purification of CRT from mammalian kidney. To isolate CRT,  sheep kidney was crushed and kept for 12 h in the extraction buffer. The lysate was centrifuged, and supernatant was precipitated by ammonium sulphate. The precipitate of 90 % ammonium sulphate was extensively dialyzed and loaded on DEAE-Hi-Trap FF and Mono Q chromatography columns. The purity of CRT was confirmed by SDS-PAGE. Finally, the protein was identified by matrix-assisted laser desorption/ionization time of flight. The purified protein was further characterized for secondary structural elements using the far-UV circular dichroism measurements. Our purification procedure is fast and simple with high yield. PMID:25149453

Dar, Mohammad Aasif; Wahiduzzaman; Islam, Asimul; Hassan, Md Imtaiyaz; Ahmad, Faizan

2014-11-01

126

Hepatitis B virus-induced calreticulin protein is involved in IFN resistance.  

PubMed

IFN-? is a widely used treatment for hepatitis B virus (HBV) infection, and IFN resistance caused by viral and/or host factors is currently a challenging clinical problem. A better understanding of the molecular mechanisms underlying IFN immunotherapy in the treatment of viral infection would be very beneficial clinically and is of immense clinical importance. Calreticulin (CRT) is an endoplasmic reticulum luminal calcium-binding chaperone that is involved in the regulation of calcium homoeostasis, the folding of newly synthesized proteins, and many other cellular functions. However, little is known about the role of CRT in HBV infection. In this study, we observed high levels of CRT expression in the sera and PBMCs of patients with HBV relative to those of healthy individuals. HBV upregulated the expression of CRT at the transcriptional level. Further investigation showed that HBV-induced CRT enhanced HBV replication by antagonizing the IFN pathway. CRT suppressed the production of endogenous IFN-? by reducing the nuclear translocation of IFN regulatory factor-7 but not IFN regulatory factor-3. Furthermore, CRT also suppressed the antiviral activity of IFN-? by inhibiting the phosphorylation of STAT1 and decreasing the expression of two IFN-? downstream effectors, protein kinase R and 2',5'-oligoadenylate synthetase. Our results offer new insights into the pathogenesis of HBV infection and may provide potential targets for anti-HBV therapy. PMID:22661095

Yue, Xin; Wang, Hui; Zhao, Fanpeng; Liu, Shi; Wu, Jianguo; Ren, Wendan; Zhu, Ying

2012-07-01

127

Oxidative stress-induced calreticulin expression and translocation: new insights into the destruction of melanocytes.  

PubMed

Increased reactive oxygen species (ROS) contribute to melanocyte apoptosis and the development of cutaneous diseases or disorders via autoimmunity. However, the mechanisms and interrelationships between ROS and autoimmunity are unknown. This study aimed to investigate the role of calreticulin (CRT) in hydrogen peroxide (H2O2)-induced apoptosis in melanocytes. Total CRT levels increased in a time-dependent manner in human immortalized normal and vitiligo melanocytes exposed to H2O2-induced oxidative stress, and surface levels of CRT were increased. Moreover, CRT overexpression increased H2O2-induced apoptosis, whereas knockdown showed the opposite results. Furthermore, CRT-treated peripheral blood mononuclear cells (PBMCs) or stressed melanocytes expressed higher levels of IL-6 and tumor necrosis factor-? (TNF-?) than untreated cells (P<0.05); this effect was inhibited with CRT knockdown. In an in vivo model, CRT levels were positively correlated with lesion area (R=0.7582, P<0.0001) and duration of vitiligo in patients (P<0.001). ELISA analyses revealed that CRT expression was higher in vitiligo patients as compared with healthy subjects (P<0.05). These data demonstrate that CRT exposure via H2O2-induced oxidative stress plays a significant role in melanocyte apoptosis and suggest a relationship between apoptosis and immune reactions during melanocyte destruction. PMID:23771121

Zhang, Yajun; Liu, Ling; Jin, Liang; Yi, Xiuli; Dang, Erle; Yang, Yang; Li, Chunying; Gao, Tianwen

2014-01-01

128

Self-oligomerization is essential for enhanced immunological activities of soluble recombinant calreticulin.  

PubMed

We have recently reported that calreticulin (CRT), a luminal resident protein, can be found in the sera of patients with rheumatoid arthritis and also that recombinant CRT (rCRT) exhibits extraordinarily strong immunological activities. We herein further demonstrate that rCRT fragments 18-412 (rCRT/18-412), rCRT/39-272, rCRT/120-308 and rCRT/120-250 can self-oligomerize in solution and are 50-100 fold more potent than native CRT (nCRT, isolated from mouse livers) in activating macrophages in vitro. We narrowed down the active site of CRT to residues 150-230, the activity of which also depends on dimerization. By contrast, rCRT/18-197 is almost completely inactive. When rCRT/18-412 is fractionated into oligomers and monomers by gel filtration, the oligomers maintain most of their immunological activities in terms of activating macrophages in vitro and inducing specific antibodies in vivo, while the monomers were much less active by comparison. Additionally, rCRT/18-412 oligomers are much better than monomers in binding to, and uptake by, macrophages. Inhibition of macrophage endocytosis partially blocks the stimulatory effect of rCRT/18-412. We conclude that the immunologically active site of CRT maps between residues 198-230 and that soluble CRT could acquire potent immuno-pathological activities in microenvironments favoring its oligomerization. PMID:23762269

Huang, Shang-Hui; Zhao, Li-Xiang; Hong, Chao; Duo, Cui-Cui; Guo, Bing-Nan; Zhang, Li-Juan; Gong, Zheng; Xiong, Si-Dong; Gong, Fang-Yuan; Gao, Xiao-Ming

2013-01-01

129

Immunogenic tumor cell death for optimal anticancer therapy: the calreticulin exposure pathway.  

PubMed

In response to some chemotherapeutic agents such as anthracyclines and oxaliplatin, cancer cells undergo immunogenic apoptosis, meaning that their corpses are engulfed by dendritic cells and that tumor cell antigens are presented to tumor-specific CD8(+) T cells, which then control residual tumor cells. One of the peculiarities of immunogenic apoptosis is the early cell surface exposure of calreticulin (CRT), a protein that usually resides in the lumen of the endoplasmic reticulum (ER). When elicited by anthracyclines or oxaliplatin, the CRT exposure pathway is activated by pre-apoptotic ER stress and the phosphorylation of the eukaryotic translation initiation factor eIF2alpha by the kinase PERK, followed by caspase-8-mediated proteolysis of the ER-sessile protein BAP31, activation of the pro-apoptotic proteins Bax and Bak, anterograde transport of CRT from the ER to the Golgi apparatus and exocytosis of CRT-containing vesicles, finally resulting in CRT translocation onto the plasma membrane surface. Interruption of this complex pathway abolishes CRT exposure, annihilates the immunogenicity of apoptosis, and reduces the immune response elicited by anticancer chemotherapies. We speculate that human cancers that are incapable of activating the CRT exposure pathway are refractory to the immune-mediated component of anticancer therapies. PMID:20421432

Zitvogel, Laurence; Kepp, Oliver; Senovilla, Laura; Menger, Laurie; Chaput, Nathalie; Kroemer, Guido

2010-06-15

130

Calreticulin expression and localization in plant cells during pollen-pistil interactions.  

PubMed

In this report, the distributions of calreticulin (CRT) and its transcripts in Haemanthus pollen, pollen tubes, and somatic cells of the hollow pistil were studied. Immunoblot analysis of protein extracts from mature anthers, dry and germinated pollen, growing pollen tubes, and unpollinated/pollinated pistils revealed a strong expression of CRT. Both in vitro and in situ studies confirmed the presence of CRT mRNA and protein in pollen/pollen tubes and somatic cells of the pistil transmitting tract. The co-localization of these molecules in ER of these cells suggests that the rough ER is a site of CRT translation. In the pistil, accumulation of the protein in pollen tubes, transmitting tract epidermis (tte), and micropylar cells of the ovule (mc) was correlated with the increased level of exchangeable calcium. Therefore, CRT as a Ca(2+)-binding/buffering protein, may be involved in mechanism of regulation calcium homeostasis in these cells. The functional role of the protein in pollen-pistil interactions, apart from its postulated function in cellular Ca(2+) homeostasis, is discussed. PMID:19820965

Lenartowska, Marta; Lenartowski, Robert; Smoli?ski, Dariusz Jan; Wróbel, Bogdan; Niedojad?o, Janusz; Jaworski, Krzysztof; Bednarska, Elzbieta

2009-12-01

131

Endoplasmic reticulum calcium regulates the retrotranslocation of Trypanosoma cruzi calreticulin to the cytosol.  

PubMed

For most secretory pathway proteins, crossing the endoplasmic reticulum (ER) membrane is an irreversible process. However, in some cases this flow can be reversed. For instance, misfolded proteins retained in the ER are retrotranslocated to the cytosol to be degraded by the proteasome. This mechanism, known as ER associated degradation (ERAD), is exploited by several bacterial toxins to gain access to the cytosol. Interestingly, some ER resident proteins can also be detected in the cytosol or nucleus, calreticulin (CRT) being the most studied. Here we show that in Trypanosoma cruzi a minor fraction of CRT localized to the cytosol. ER calcium depletion, but not increasing cytosolic calcium, triggered the retrotranslocation of CRT in a relatively short period of time. Cytosolic CRT was subsequently degraded by the proteasome. Interestingly, the single disulfide bridge of CRT is reduced when the protein is located in the cytosol. The effect exerted by ER calcium was strictly dependent on the C-terminal domain (CRT-C), since a CRT lacking it was totally retained in the ER, whereas the localization of an unrelated protein fused to CRT-C mirrored that of endogenous CRT. This finding expands the regulatory mechanisms of protein sorting and may represent a new crossroad between diverse physiological processes. PMID:20957192

Labriola, Carlos A; Conte, Ianina L; López Medus, Máximo; Parodi, Armando J; Caramelo, Julio J

2010-01-01

132

Calreticulin controls the rate of assembly of CD1d molecules in the endoplasmic reticulum.  

PubMed

CD1d is an MHC class I-like molecule comprised of a transmembrane glycoprotein (heavy chain) associated with ?(2)-microglobulin (?(2)m) that presents lipid antigens to NKT cells. Initial folding of the heavy chain involves its glycan-dependent association with calreticulin (CRT), calnexin (CNX), and the thiol oxidoreductase ERp57, and is followed by assembly with ?(2)m to form the heterodimer. Here we show that in CRT-deficient cells CD1d heavy chains convert to ?(2)m-associated dimers at an accelerated rate, indicating faster folding of the heavy chain, while the rate of intracellular transport after assembly is unaffected. Unlike the situation with MHC class I molecules, antigen presentation by CD1d is not impaired in the absence of CRT. Instead, there are elevated levels of stable and functional CD1d on the surface of CRT-deficient cells. Association of the heavy chains with the ER chaperones Grp94 and Bip is observed in the absence of CRT, and these may replace CRT in mediating CD1d folding and assembly. ER retention of free CD1d heavy chains is impaired in CRT-deficient cells, allowing their escape and subsequent expression on the plasma membrane. However, these free heavy chains are rapidly internalized and degraded in lysosomes, indicating that ?(2)m association is required for the exceptional resistance of CD1d to lysosomal degradation that is normally observed. PMID:20861015

Zhu, Yajuan; Zhang, Wei; Veerapen, Natacha; Besra, Gurdyal; Cresswell, Peter

2010-12-01

133

Disruption of the PP1/GADD34 complex induces calreticulin exposure.  

PubMed

In response to some chemotherapeutic agents, tumor cells can translocate calreticulin (CRT), which is usually contained in the lumen of the endoplasmic reticulum, to the surface of the plasma membrane. This effect requires the phosphorylation of the eukaryotic initiation factor 2alpha(eIF2alpha) by the eIF2alpha kinase PERK, yet may also be triggered by inhibition of the eIF2alpha phosphatase, which is composed by a catalytic subunit (PP1) and a regulatory subunit (GADD34). Here, we addressed the question whether the dissociation of the PP1/GADD34 complex would be sufficient to trigger CRT exposure. Molecular modeling led to the design of a GADD34-derived peptide that competitively disrupts the PP1/GADD34 complex. When added to intact cells, the GADD34-derived peptide fused to a plasma membrane translocation domain abolished the interaction between PP1 and GADD34, stimulated the phosphorylation of eIF2alpha, and triggered CRT exposure. However, the resolution of the PP1/GADD34 complex did not evoke apoptosis, allowing for the dissociation of CRT exposure and cell death. Anthracyclins, which are highly efficient in inducing CRT translocation to the cell surface also stimulated the dissociation of the PP1/GADD34 complex. These results suggest that the PP1/GADD34 complex plays a major role in the regulation of CRT exposure. PMID:19901557

Kepp, Oliver; Galluzzi, Lorenzo; Giordanetto, Fabrizio; Tesniere, Antoine; Vitale, Ilio; Martins, Isabelle; Schlemmer, Frederic; Adjemian, Sandy; Zitvogel, Laurence; Kroemer, Guido

2009-12-01

134

Calreticulin maintains the low threshold of peptide required for efficient antigen presentation.  

PubMed

Calreticulin (CRT) plays a critical role in MHC class I antigen processing and elicits peptide-specific CD8(+) T cell responses against tumours when administered with peptides. However, how CRT contributes to class I antigen processing and the mechanism of its adjuvant effect in anti-tumour responses, remain to be elucidated. Here we show that reduced class I expression in CRT deficient cells can be restored by the direct delivery of peptides into the ER or by incubation at low temperature. CRT deficient cells exhibited a TAP-deficient phenotype in terms of class I assembly, without loss of TAP expression or functionality. Furthermore, a higher concentration of antigen in the cytosol is required for specific T cell stimulation, suggesting that CRT has a functional role in the maintenance of the low peptide concentration threshold required in the ER for efficient antigen presentation. In the absence of CRT, ERp57 is up-regulated, which indicates that they collaborate with each other in class I antigen processing. PMID:19748124

Fu, Hongmei; Liu, Changzhen; Flutter, Barry; Tao, Hua; Gao, Bin

2009-10-01

135

Ovalbumin-derived precursor peptides are transferred sequentially from gp96 and calreticulin to MHC class I in the endoplasmic reticulum.  

PubMed

Cellular peptides generated by proteasomal degradation of proteins in the cytosol and destined for presentation by MHC class I (MHC-I) are associated with several chaperones. Heat shock proteins 70, 90, and the TCP-1 ring complex have been implicated as important cytosolic players for chaperoning these peptides. In this study, we report that gp96 and calreticulin are essential for chaperoning peptides in the endoplasmic reticulum. Importantly, we demonstrate that cellular peptides are transferred sequentially from gp96 to calreticulin and then to MHC-I forming a relay line. Disruption of this relay line by removal of gp96 or calreticulin prevents the binding of peptides by MHC-I and hence presentation of the MHC-I-peptide complex on the cell surface. Our results are important for understanding how peptides are processed and trafficked within the endoplasmic reticulum before exiting in association with MHC-I H chains and beta2-microglobulin as a trimolecular complex. PMID:20410492

Kropp, Laura E; Garg, Manish; Binder, Robert J

2010-05-15

136

Dendritic cell surface calreticulin is a receptor for NY-ESO-1: direct interactions between tumor-associated antigen and the innate immune system.  

PubMed

How the immune system recognizes endogenously arising tumors and elicits adaptive immune responses against nonmutated tumor-associated Ags is poorly understood. In search of intrinsic factors contributing to the immunogenicity of the tumor-associated Ag NY-ESO-1, we found that the NY-ESO-1 protein binds to the surface of immature dendritic cells (DC), macrophages, and monocytes, but not to that of B cells or T cells. Using immunoprecipitation coupled with tandem mass spectrometry, we isolated DC surface calreticulin as the receptor for NY-ESO-1. Calreticulin Abs blocked NY-ESO-1 binding on immature DC and its cross-presentation to CD8+ T cells in vitro. Calreticulin/NY-ESO-1 interactions provide a direct link between NY-ESO-1, the innate immune system, and, potentially, the adaptive immune response against NY-ESO-1. PMID:16951317

Zeng, Gang; Aldridge, Michael E; Tian, Xiaoli; Seiler, Daniel; Zhang, Xiaolong; Jin, Yusheng; Rao, Jianyu; Li, Weidong; Chen, Dequan; Langford, Marlyn P; Duggan, Chris; Belldegrun, Arie S; Dubinett, Steven M

2006-09-15

137

Suppressive effects of FR167653, an inhibitor of p38 mitogen-activated kinase, on calreticulin mRNA expression induced by endoplasmic reticulum stresses  

Microsoft Academic Search

Several endoplasmic reticulum chaperones are simultaneously transactivated in response to various forms of endoplasmic reticulum stresses. Calreticulin is one such chaperone. We here show that the compound FR167653 {1-[7-(4-fluorophenyl)-1,2,3,4-tetrahydro-8-(4-pyridyl)pyrazolo[5,1-c][1,2,4]triazin-2-yl]-2-phenylethanedione sulfate monohydrate} suppresses the transactivation of calreticulin following endoplasmic reticulum stress. FR167653, like SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-imidazole], has been reported to inhibit p38 mitogen-activated kinase (p38 MAPK). In this study, FR167653 concentration-dependently inhibited

Takao Yamazaki; Masakazu Muramoto; Shintaro Nishimura; Yasuhiro Kita

2004-01-01

138

Overexpression of calreticulin contributes to the development and progression of pancreatic cancer.  

PubMed

We studied the clinicopathological significance for Calreticulin (CRT) expression in pancreatic cancer (PC), and its functional relationship with other signaling genes (especially with p53) in regulating the biological behavior of PC cells. IHC, IF, IB, and real-time PCR were used to detect CRT expression in PC, while transfection and drug intervention were used to investigate the functional relationship of CRT with other signaling genes. IHC showed both CRT and p53 expression was significantly increased in PC, compared to that in paired non-cancerous pancreatic tissues (P?

Sheng, Weiwei; Chen, Chuanping; Dong, Ming; Zhou, Jianping; Liu, Qingfeng; Dong, Qi; Li, Feng

2014-07-01

139

Novel evidence of the involvement of calreticulin in major psychiatric disorders.  

PubMed

Calreticulin (CALR) is a multi-functional protein that is strictly conserved across species. Two mRNA transcripts have been recognized for the CALR gene in humans, which use a common promoter sequence. We have recently reported mutations in the CALR promoter that co-occur with psychosis. One of those mutations at -220A increases gene expression in human BE(2)-C and HEK-293 cell lines. This mutation is the first instance of a functional cognition-deficit mutation reversing a human gene promoter to the primitive type. In the current study, we analyzed the effect of the most widely-used mood-stabilizing drug, valproic acid (VPA), on nucleotide -220 in two neuronal cell lines, LAN-5 and N2A. Remarkably, VPA increased gene expression in the cells with the wild-type -220C construct, whereas a dramatic decrease in gene expression was observed in the cell lines with the mutant construct (p<0.000004 and p<0.016, respectively). We also sequenced the 600-bp CALR promoter, and the highly conserved intron 1 sequence in an independent sample of patients afflicted with major psychiatric disorders and controls. A new case of major depressive disorder with psychotic features with the -220A mutation was identified. A novel 1-bp insertion was also detected in intron 1 at IVSI-310, in a case of amphetamine-induced psychosis. As for the psychosis-linked CALR promoter mutations identified to-date, the IVSI mutation was not detected in the control pool. This mutation creates a RREB-1 transcription factor binding site within the first intron. Our present findings identify the site of action of VPA in the CALR promoter, and introduce a novel mutation in a case of substance-induced psychosis in the first intron of CALR. PMID:22507216

Ohadi, M; Mirabzadeh, A; Esmaeilzadeh-Gharehdaghi, E; Rezazadeh, M; Hosseinkhanni, S; Oladnabi, M; Firouzabadi, S Ghasemi; Darvish, H

2012-06-01

140

Calreticulin promotes angiogenesis via activating nitric oxide signalling pathway in rheumatoid arthritis.  

PubMed

Calreticulin (CRT) is a multi-functional endoplasmic reticulum protein implicated in the pathogenesis of rheumatoid arthritis (RA). The present study was undertaken to determine whether CRT was involved in angiogenesis via the activating nitric oxide (NO) signalling pathway. We explored the profile of CRT expression in RA (including serum, synovial fluid and synovial tissue). In order to investigate the role of CRT on angiogenesis, human umbilical vein endothelial cells (HUVECs) were isolated and cultured in this study for in-vitro experiments. Our results showed a significantly higher concentration of CRT in serum (5·4?±?2·2?ng/ml) of RA patients compared to that of osteoarthritis (OA, 3·6?±?0·9?ng/ml, P?

Ding, H; Hong, C; Wang, Y; Liu, J; Zhang, N; Shen, C; Wei, W; Zheng, F

2014-11-01

141

Radiation-induced immunogenic modulation of tumor enhances antigen processing and calreticulin exposure, resulting in enhanced T-cell killing.  

PubMed

Radiation therapy (RT) is used for local tumor control through direct killing of tumor cells. Radiation-induced cell death can trigger tumor antigen-specific immune responses, but these are often noncurative. Radiation has been demonstrated to induce immunogenic modulation (IM) in various tumor types by altering the biology of surviving cells to render them more susceptible to T cell-mediated killing. Little is known about the mechanism(s) underlying IM elicited by sub-lethal radiation dosing. We have examined the molecular and immunogenic consequences of radiation exposure in breast, lung, and prostate human carcinoma cells. Radiation induced secretion of ATP and HMGB1 in both dying and surviving tumor cells. In vitro and in vivo tumor irradiation induced significant upregulation of multiple components of the antigen-processing machinery and calreticulin cell-surface expression. Augmented CTL lysis specific for several tumor-associated antigens was largely dictated by the presence of calreticulin on the surface of tumor cells and constituted an adaptive response to endoplasmic reticulum stress, mediated by activation of the unfolded protein response. This study provides evidence that radiation induces a continuum of immunogenic alterations in tumor biology, from immunogenic modulation to immunogenic cell death. We also expand the concept of immunogenic modulation, where surviving tumor cells recovering from radiation-induced endoplasmic reticulum stress become more sensitive to CTL killing. These observations offer a rationale for the combined use of radiation with immunotherapy, including for patients failing RT alone. PMID:24480782

Gameiro, Sofia R; Jammeh, Momodou L; Wattenberg, Max M; Tsang, Kwong Y; Ferrone, Soldano; Hodge, James W

2014-01-30

142

Calnexin, calreticulin, and ERp57 cooperate in disulfide bond formation in human CD1d heavy chain.  

PubMed

Members of the CD1 family of membrane glycoproteins can present antigenic lipids to T lymphocytes. Like major histocompatibility complex class I molecules, they form a heterodimeric complex of a heavy chain and beta(2)-microglobulin (beta(2)m) in the endoplasmic reticulum (ER). Binding of lipid antigens, however, takes place in endosomal compartments, similar to class II molecules, and on the plasma membrane. Unlike major histocompatibility complex class I or CD1b molecules, which need beta(2)m to exit the ER, CD1d can be expressed on the cell surface as either a free heavy chain or associated with beta(2)m. These differences led us to investigate early events of CD1d biosynthesis and maturation and the role of ER chaperones in its assembly. Here we show that CD1d associates in the ER with both calnexin and calreticulin and with the thiol oxidoreductase ERp57 in a manner dependent on glucose trimming of its N-linked glycans. Complete disulfide bond formation in the CD1d heavy chain was substantially impaired if the chaperone interactions were blocked by the glucosidase inhibitors castanospermine or N-butyldeoxynojirimycin. The formation of at least one of the disulfide bonds in the CD1d heavy chain is coupled to its glucose trimming-dependent association with ERp57, calnexin, and calreticulin. PMID:12239218

Kang, Suk-Jo; Cresswell, Peter

2002-11-22

143

Radiation-induced immunogenic modulation of tumor enhances antigen processing and calreticulin exposure, resulting in enhanced T-cell killing  

PubMed Central

Radiation therapy (RT) is used for local tumor control through direct killing of tumor cells. Radiation-induced cell death can trigger tumor antigen-specific immune responses, but these are often noncurative. Radiation has been demonstrated to induce immunogenic modulation (IM) in various tumor types by altering the biology of surviving cells to render them more susceptible to T cell-mediated killing. Little is known about the mechanism(s) underlying IM elicited by sub-lethal radiation dosing. We have examined the molecular and immunogenic consequences of radiation exposure in breast, lung, and prostate human carcinoma cells. Radiation induced secretion of ATP and HMGB1 in both dying and surviving tumor cells. In vitro and in vivo tumor irradiation induced significant upregulation of multiple components of the antigen-processing machinery and calreticulin cell-surface expression. Augmented CTL lysis specific for several tumor-associated antigens was largely dictated by the presence of calreticulin on the surface of tumor cells and constituted an adaptive response to endoplasmic reticulum stress, mediated by activation of the unfolded protein response. This study provides evidence that radiation induces a continuum of immunogenic alterations in tumor biology, from immunogenic modulation to immunogenic cell death. We also expand the concept of immunogenic modulation, where surviving tumor cells recovering from radiation-induced endoplasmic reticulum stress become more sensitive to CTL killing. These observations offer a rationale for the combined use of radiation with immunotherapy, including for patients failing RT alone. PMID:24480782

Gameiro, Sofia R.; Jammed, Momodou L.; Wattenberg, Max M.; Tsang, Kwong Y.; Ferrone, Soldano; Hodge, James W.

2014-01-01

144

Calreticulin is crucial for calcium homeostasis mediated adaptation and survival of thick ascending limb of Henle's loop cells under osmotic stress  

Microsoft Academic Search

The thick ascending limb of Henle's loop (TALH) is normally exposed to variable and often very high osmotic stress and involves different mechanisms to counteract this stress. ER resident calcium binding proteins especially calreticulin (CALR) play an important role in different stress balance mechanisms. To investigate the role of CALR in renal epithelial cells adaptation and survival under osmotic stress,

Asima Bibi; Nitin K. Agarwal; Gry H. Dihazi; Marwa Eltoweissy; Phuc Van Nguyen; Gerhard A. Mueller; Hassan Dihazi

2011-01-01

145

Quality Control in the Secretory Pathway: The Role of Calreticulin, Calnexin and BiP in the Retention of Glycoproteins with C-Terminal Truncations  

PubMed Central

Unlike properly folded and assembled proteins, most misfolded and incompletely assembled proteins are retained in the endoplasmic reticulum of mammalian cells and degraded without transport to the Golgi complex. To analyze the mechanisms underlying this unique sorting process and its fidelity, the fate of C-terminally truncated fragments of influenza hemagglutinin was determined. An assortment of different fragments was generated by adding puromycin at low concentrations to influenza virus-infected tissue culture cells. Of the fragments generated, <2% was secreted, indicating that the system for detecting defects in newly synthesized proteins is quite stringent. The majority of secreted species corresponded to folding domains within the viral spike glycoprotein. The retained fragments acquired a partially folded structure with intrachain disulfide bonds and conformation-dependent antigenic epitopes. They associated with two lectin-like endoplasmic reticulum chaperones (calnexin and calreticulin) but not BiP/GRP78. Inhibition of the association with calnexin and calreticulin by the addition of castanospermine significantly increased fragment secretion. However, it also caused association with BiP/GRP78. These results indicated that the association with calnexin and calreticulin was involved in retaining the fragments. They also suggested that BiP/GRP78 could serve as a backup for calnexin and calreticulin in retaining the fragments. In summary, the results showed that the quality control system in the secretory pathway was efficient and sensitive to folding defects, and that it involved multiple interactions with endoplasmic reticulum chaperones. PMID:9348535

Zhang, Jian-Xin; Braakman, Ineke; Matlack, Kent E.S.; Helenius, Ari

1997-01-01

146

Reversion of the human calreticulin gene promoter to the ancestral type as a result of a novel psychosis-associated mutation  

Microsoft Academic Search

Development-dependent, tissue-specific expression of the calreticulin (CALR) gene in the gray matter coincides with the expression of psychoses phenotypes. We have recently reported instances of mutations within the core promoter sequence of the gene in schizoaffective disorder. In view of the mounting evidence on the genetic overlap in the psychiatric spectrum, we investigated this gene in a spectrum of patients

T. Farokhashtiani; A. Mirabzadeh; M. Olad Nabi; Z. Ghaem Magham; H. R. Khorram Khorshid; H. Najmabadi; M. Ohadi

2011-01-01

147

Overexpression of Calreticulin Increases the Ca 2 ÷ Capacity of Rapidly Exchanging Ca 2 ÷ Stores and Reveals Aspects of Their Lumenal Microenvironment and Function  

Microsoft Academic Search

A molecularly tagged form of calreticulin (CR), a low affinity-high capacity Ca 2+ binding protein that resides in the ER lumen, was transiently trans- fected into HeLa cells to specifically modify the Ca 2÷ buffering capacity of the intracellular Ca 2÷ stores. Fluo- rescence and confocal microscope immunocytochemis- try revealed the tagged protein to be expressed by over 40% of

Carlo Bastianutto; Emilio Clementi; Franca Codazzi; Paola Podini; Francesca De Giorgi; Rosario Rizzuto; Jacopo Meldolesi; Tullio Pozzan

148

Human survivin and Trypanosoma cruzi calreticulin act in synergy against a murine melanoma in vivo.  

PubMed

Immune-based anti-tumor or anti-angiogenic therapies hold considerable promise for the treatment of cancer. The first approach seeks to activate tumor antigen-specific T lymphocytes while, the second, delays tumor growth by interfering with blood supply. Tumor Associated Antigens are often employed to target tumors with therapeutic drugs, but some are also essential for tumor viability. Survivin (Surv) is a member of the inhibitor of apoptosis protein family that is considered a Tumor Associated Antigen important for cancer cell viability and proliferation. On the other hand, Trypanosoma cruzi (the agent of Chagas' disease) calreticulin (TcCRT) displays remarkable anti-angiogenic properties. Because these molecules are associated with different tumor targets, we reasoned that immunization with a Surv-encoding plasmid (pSurv) and concomitant TcCRT administration should generate a stronger anti-tumor response than application of either treatment separately. To evaluate this possibility, C57BL/6 mice were immunized with pSurv and challenged with an isogenic melanoma cell line that had been pre-incubated with recombinant TcCRT (rTcCRT). Following tumor cell inoculation, mice were injected with additional doses of rTcCRT. For the combined regimen we observed in mice that: i). Tumor growth was impaired, ii). Humoral anti-rTcCRT immunity was induced and, iii). In vitro rTcCRT bound to melanocytes, thereby promoting the incorporation of human C1q and subsequent macrophage phagocytosis of tumor cells. These observations are interpreted to reflect the consequence of the following sequence of events: rTcCRT anti-angiogenic activity leads to stress in tumor cells. Murine CRT is then translocated to the external membrane where, together with rTcCRT, complement C1 is captured, thus promoting tumor phagocytosis. Presentation of the Tumor Associated Antigen Surv induces the adaptive anti-tumor immunity and, independently, mediates anti-endothelial cell immunity leading to an important delay in tumor growth. PMID:24755644

Aguilar-Guzmán, Lorena; Lobos-González, Lorena; Rosas, Carlos; Vallejos, Gerardo; Falcón, Cristián; Sosoniuk, Eduardo; Coddou, Francisca; Leyton, Lisette; Lemus, David; Quest, Andrew F G; Ferreira, Arturo

2014-01-01

149

Human Survivin and Trypanosoma cruzi Calreticulin Act in Synergy against a Murine Melanoma In Vivo  

PubMed Central

Immune-based anti-tumor or anti-angiogenic therapies hold considerable promise for the treatment of cancer. The first approach seeks to activate tumor antigen-specific T lymphocytes while, the second, delays tumor growth by interfering with blood supply. Tumor Associated Antigens are often employed to target tumors with therapeutic drugs, but some are also essential for tumor viability. Survivin (Surv) is a member of the inhibitor of apoptosis protein family that is considered a Tumor Associated Antigen important for cancer cell viability and proliferation. On the other hand, Trypanosoma cruzi (the agent of Chagas’ disease) calreticulin (TcCRT) displays remarkable anti-angiogenic properties. Because these molecules are associated with different tumor targets, we reasoned that immunization with a Surv-encoding plasmid (pSurv) and concomitant TcCRT administration should generate a stronger anti-tumor response than application of either treatment separately. To evaluate this possibility, C57BL/6 mice were immunized with pSurv and challenged with an isogenic melanoma cell line that had been pre-incubated with recombinant TcCRT (rTcCRT). Following tumor cell inoculation, mice were injected with additional doses of rTcCRT. For the combined regimen we observed in mice that: i). Tumor growth was impaired, ii). Humoral anti-rTcCRT immunity was induced and, iii). In vitro rTcCRT bound to melanocytes, thereby promoting the incorporation of human C1q and subsequent macrophage phagocytosis of tumor cells. These observations are interpreted to reflect the consequence of the following sequence of events: rTcCRT anti-angiogenic activity leads to stress in tumor cells. Murine CRT is then translocated to the external membrane where, together with rTcCRT, complement C1 is captured, thus promoting tumor phagocytosis. Presentation of the Tumor Associated Antigen Surv induces the adaptive anti-tumor immunity and, independently, mediates anti-endothelial cell immunity leading to an important delay in tumor growth. PMID:24755644

Aguilar-Guzman, Lorena; Lobos-Gonzalez, Lorena; Rosas, Carlos; Vallejos, Gerardo; Falcon, Cristian; Sosoniuk, Eduardo; Coddou, Francisca; Leyton, Lisette; Lemus, David; Quest, Andrew F. G.; Ferreira, Arturo

2014-01-01

150

Molecular insight into the effect of lipid bilayer environments on thrombospondin-1 and calreticulin interactions.  

PubMed

Thrombospondin-1 (TSP1) binding to cell surface calreticulin (CRT) stimulates the association of CRT with low-density lipoprotein (LDL) receptor-related protein (LRP1) to signal focal adhesion disassembly and engagement of cellular activities. A recent study demonstrated that membrane rafts are necessary for TSP1-mediated focal adhesion disassembly, but the molecular role of membrane rafts in mediating TSP1-CRT-LRP1 signaling is unknown. In this study, we investigated the effect of lipid bilayer environments on TSP1 and CRT interactions via atomically detailed molecular dynamics simulations. Results showed that the microscopic structural properties of lipid molecules and mesoscopic mechanical properties and electrostatic potential of the bilayer were significantly different between a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer and a raftlike lipid bilayer [a POPC/cholesterol (CHOL) raftlike lipid bilayer or a POPC/CHOL/sphingomyelin (SM) raftlike lipid bilayer], and the difference was enhanced by SM lipids in a raftlike lipid bilayer. These bilayer property differences affect the interactions of CRT with the bilayer, further influencing CRT conformation and TSP1-CRT interactions. A raftlike lipid bilayer stabilized CRT conformation as compared to a POPC bilayer environment. TSP1 binding to CRT resulted in a conformation for the CRT N-domain more "open" than that of the CRT P-domain in a raftlike lipid bilayer environment, which could facilitate binding of CRT to LRP1 to engage downstream signaling. The open conformational changes of CRT by binding to TSP1 in a raftlike lipid bilayer were enhanced by SM lipids in a lipid bilayer. The direct interactions of both the N- and P-domains of CRT with the bilayer contribute to the more open conformation of CRT in the TSP1-CRT complex on a raftlike lipid bilayer as compared to that on a POPC bilayer. The interactions of CRT or the TSP1-CRT complex with the lipid bilayer also caused CHOL molecules and/or lipids to be more coordinated and to aggregate into patchlike regions in the raftlike lipid bilayers. The lipid and CHOL molecule coordination and aggregation could in turn affect the interactions of CRT with the membrane raft, thereby altering TSP1-CRT interactions and CRT conformational changes that potentially regulate its interactions with LRP1. This study provides molecular insights into the role of lipid bilayer environments in TSP1-CRT interactions and in the CRT conformational changes that are predicted to facilitate binding of CRT to LRP1 to engage downstream signaling events. PMID:25260145

Wang, Lingyun; Murphy-Ullrich, Joanne E; Song, Yuhua

2014-10-14

151

Mechanistic studies on iridium catalyzed allylic substitution.  

E-print Network

??Mechanistic studies on iridium catalyzed allylic substitution reactions catalyzed by iridium phosphoramidite complexes revealed that the active catalyst is generated through a base assisted cyclometalation… (more)

Madrahimov, Sherzod

2012-01-01

152

The endoplasmic reticulum chaperone calreticulin is recruited to the uropod during capping of surface receptors in Entamoeba histolytica.  

PubMed

Calreticulin (CRT), an intracellular chaperone protein, is crucial for proper folding and transport of proteins through the endoplasmic reticulum (ER). It has recently been identified as a critical regulator of some several different cellular functions such as migration, phagocytosis of apoptotic cells and cytotoxic T lymphocyte- or natural killer cell-mediated lysis. Characterization of CRT isolated from parasites may thus help to decipher the contribution of this protein in the parasites' biology and host-parasite interactions. Here, we report descriptive data on the localization of Entamoeba histolytica's CRT at rest and following cap formation by Concanavalin A. As expected, CRT from E. histolytica localizes in the ER. However, the protein was surprisingly found to localize to the parasite surface and, furthermore, to concentrate in the uropod following activation of surface receptors by capping with Concanavalin A. PMID:18160113

Girard-Misguich, Fabienne; Sachse, Martin; Santi-Rocca, Julien; Guillén, Nancy

2008-02-01

153

Lysyl tRNA synthetase is required for the translocation of calreticulin to the cell surface in immunogenic death.  

PubMed

In response to immunogenic cell death inducers, calreticulin (CRT) translocates from its orthotopic localization in the lumen of the endoplasmic reticulum (ER) to the surface of the plasma membrane where it serves as an engulfment signal for antigen-presenting cells.(1) Here, we report that yet another ER protein, the lysyl-tRNA synthetase (KARS), was exposed on the surface of stressed cells, on which KARS co-localized with CRT in lipid rafts. Depletion of KARS with small interfering RNAs suppressed CRT exposure induced by anthracyclines or UVC light. In contrast to CRT, KARS was also found in the supernatant of stressed cells. Recombinant KARS protein was unable to influence the binding of recombinant CRT to the cell surface. Moreover, recombinant KARS protein was unable to stimulate macrophages in vitro. These results underscore the contribution of KARS to the emission of (one of) the principal signal(s) of immunogenic cell death, CRT exposure. PMID:20699648

Kepp, Oliver; Gdoura, Abdelaziz; Martins, Isabelle; Panaretakis, Theocharis; Schlemmer, Frederic; Tesniere, Antoine; Fimia, Gian Maria; Ciccosanti, Fabiola; Burgevin, Anne; Piacentini, Mauro; Eggleton, Paul; Young, Philip J; Zitvogel, Laurence; van Endert, Peter; Kroemer, Guido

2010-08-01

154

Calreticulin, a peptide-binding chaperone of the endoplasmic reticulum, elicits tumor- and peptide-specific immunity.  

PubMed

Calreticulin (CRT), a peptide-binding heat shock protein (HSP) of the endoplasmic reticulum (ER), has been shown previously to associate with peptides transported into the ER by transporter associated with antigen processing (Spee, P., and J. Neefjes. 1997. Eur. J. Immunol. 27: 2441-2449). Our studies show that CRT preparations purified from tumors elicit specific immunity to the tumor used as the source of CRT but not to an antigenically distinct tumor. The immunogenicity is attributed to the peptides associated with the CRT molecule and not to the CRT molecule per se. It is further shown that CRT molecules can be complexed in vitro to unglycosylated peptides and used to elicit peptide-specific CD8(+) T cell response in spite of exogenous administration. These characteristics of CRT closely resemble those of HSPs gp96, hsp90, and hsp70, although CRT has no apparent structural homologies to them. PMID:10049943

Basu, S; Srivastava, P K

1999-03-01

155

Enantioselective nucleophile-catalyzed cycloadditions  

E-print Network

Chapter 1 describes the development of an asymmetric nucleophile-catalyzed [2+2] cycloaddition of ketenes with aldehydes. This is the first report of a catalytic enantioselective synthesis of trisubstituted [beta]-lactones. ...

Wilson, Jonathan E., Ph. D. Massachusetts Institute of Technology

2007-01-01

156

Over-expression of calcium-dependent protein kinase 13 and calreticulin interacting protein 1 confers cold tolerance on rice plants  

Microsoft Academic Search

Calcium is a ubiquitous signaling molecule and changes in cytosolic calcium concentration are involved in plant responses\\u000a to various stimuli. The rice calcium-dependent protein kinase 13 (CDPK13) and calreticulin interacting protein 1 (CRTintP1)\\u000a have previously been reported to be involved in cold stress response in rice. In this study, rice lines transformed with sense\\u000a CDPK13 or CRTintP1 constructs were produced

Setsuko Komatsu; Guangxiao Yang; Monowar Khan; Haruko Onodera; Seiichi Toki; Masayuki Yamaguchi

2007-01-01

157

The n 3-polyunsaturated fatty acid docosahexaenoic acid induces immunogenic cell death in human cancer cell lines via pre-apoptotic calreticulin exposure  

Microsoft Academic Search

Some anticancer chemotherapeutics, such as anthracyclines and oxaliplatin, elicit immunogenic apoptosis, meaning that dying\\u000a cancer cells are engulfed by dendritic cells and tumor antigens are efficiently presented to CD8+ T cells, which control residual\\u000a tumor cells. Immunogenic apoptosis is characterized by pre-apoptotic cell surface exposure of calreticulin (CRT), which usually\\u000a resides into the endoplasmic reticulum. We investigated the ability of

Romina Molinari; Donatella D’Eliseo; Laura Manzi; Lello Zolla; Francesca Velotti; Nicolò Merendino

158

Root to shoot communication and abscisic acid in calreticulin ( CR) gene expression and salt-stress tolerance in grafted diploid potato clones  

Microsoft Academic Search

Potato is an important world crop but its cultivation is relatively limited by its sensitivity to salt-stress. Auto- and hetero-grafting was used to examine the effect of rootstock and abscisic acid (ABA) on expression of the Ca2+-storage protein calreticulin (CR) and salt-stress tolerance in potato. Sibling-selected diploid clones of potato (S. tuberosum) were utilized that are distinguished by differential root

Javad Shaterian; Fawzy Georges; Atta Hussain; Doug Waterer; Hielke De Jong; Karen K. Tanino

2005-01-01

159

The Interaction of Classical Complement Component C1 with Parasite and Host Calreticulin Mediates Trypanosoma cruzi Infection of Human Placenta  

PubMed Central

Background 9 million people are infected with Trypanosoma cruzi in Latin America, plus more than 300,000 in the United States, Canada, Europe, Australia, and Japan. Approximately 30% of infected individuals develop circulatory or digestive pathology. While in underdeveloped countries transmission is mainly through hematophagous arthropods, transplacental infection prevails in developed ones. Methodology/Principal Findings During infection, T. cruzi calreticulin (TcCRT) translocates from the endoplasmic reticulum to the area of flagellum emergence. There, TcCRT acts as virulence factor since it binds maternal classical complement component C1q that recognizes human calreticulin (HuCRT) in placenta, with increased parasite infectivity. As measured ex vivo by quantitative PCR in human placenta chorionic villi explants (HPCVE) (the closest available correlate of human congenital T. cruzi infection), C1q mediated up to a 3–5-fold increase in parasite load. Because anti-TcCRT and anti-HuCRT F(ab?)2 antibody fragments are devoid of their Fc-dependent capacity to recruit C1q, they reverted the C1q-mediated increase in parasite load by respectively preventing its interaction with cell-bound CRTs from both parasite and HPCVE origins. The use of competing fluid-phase recombinant HuCRT and F(ab?)2 antibody fragments anti-TcCRT corroborated this. These results are consistent with a high expression of fetal CRT on placental free chorionic villi. Increased C1q-mediated infection is paralleled by placental tissue damage, as evidenced by histopathology, a damage that is ameliorated by anti-TcCRT F(ab?)2 antibody fragments or fluid-phase HuCRT. Conclusions/Significance T. cruzi infection of HPCVE is importantly mediated by human and parasite CRTs and C1q. Most likely, C1q bridges CRT on the parasite surface with its receptor orthologue on human placental cells, thus facilitating the first encounter between the parasite and the fetal derived placental tissue. The results presented here have several potential translational medicine aspects, specifically related with the capacity of antibody fragments to inhibit the C1q/CRT interactions and thus T. cruzi infectivity. PMID:23991234

Castillo, Christian; Ramirez, Galia; Valck, Carolina; Aguilar, Lorena; Maldonado, Ismael; Rosas, Carlos; Galanti, Norbel; Kemmerling, Ulrike; Ferreira, Arturo

2013-01-01

160

Acetic Acid Catalyzed Carbon Aerogels  

Microsoft Academic Search

We prepared carbon aerogels with a wide range of structural properties and densities using the weak acetic acid as a catalyst. Two series of acetic acid catalyzed carbon aerogels with different dilution of the catalyst and the monomers were investigated accurately. Structural investigation was performed via (U)SAXS, gas sorption and SEM. The pore and particle size can be tailored according

R. Brandt; R. Petricevic; H. Pröbstle; J. Fricke

2003-01-01

161

Performance of catalyzed hydrazine in field applications  

SciTech Connect

The performance of newly developed oxygen scavengers for boilers is often compared to sulfite and hydrazine. Catalyzed hydrazine out-performs hydrazine and might be preferred when catalyzed sulfite cannot be used. Data from a Midwest Utility confirms that, under field conditions, catalyzed hydrazine out-performance hydrazine and carbohydrazine when feedwater oxygen and iron levels were critical. Catalyzed hydrazine might be preferred when high performance and economics are the primary concerns.

Allgood, T.B.

1987-01-01

162

The angiogenesis inhibitor vasostatin is regulated by neutrophil elastase-dependent cleavage of calreticulin in AML patients.  

PubMed

The calcium-binding protein calreticulin (CRT) regulates protein folding in the endoplasmic reticulum (ER) and is induced in acute myeloid leukemia (AML) cells with activation of the unfolded protein response. Intracellular CRT translocation to the cell surface induces immunogenic cell death, suggesting a role in tumor suppression. In this study, we investigated CRT regulation in the serum of patients with AML. We found that CRT is not only exposed by exocytosis on the outer cell membrane after treatment with anthracyclin but also ultimately released to the serum in vitro and in AML patients during induction therapy. Leukemic cells of 113 AML patients showed increased levels of cell-surface CRT (P < .0001) and N-terminus serum CRT (P < .0001) compared with normal myeloid cells. Neutrophil elastase was identified to cleave an N-terminus CRT peptide, which was characterized as vasostatin and blocked ATRA-triggered differentiation. Levels of serum vasostatin in patients with AML inversely correlated with bone marrow vascularization, suggesting a role in antiangiogenesis. Finally, patients with increased vasostatin levels had longer relapse-free survival (P = .04) and specifically benefited from autologous transplantation (P = .006). Our data indicate that vasostatin is released from cell-surface CRT and impairs differentiation of myeloid cells and vascularization of the bone marrow microenvironment. PMID:22915645

Mans, Sarah; Banz, Yara; Mueller, Beatrice U; Pabst, Thomas

2012-09-27

163

Calreticulin and Hsp90 stabilize the human insulin receptor and promote its mobility in the endoplasmic reticulum  

PubMed Central

Elimination of misfolded membrane proteins in the endoplasmic reticulum (ER) affects cell survival and growth and can be triggered by either local physiologic events or disease-associated mutations. Regulation of signaling receptor degradation involves both cytosolic and ER luminal molecular chaperones, but the mechanisms and timing of this process remain uncertain. Here we report that calreticulin (CRT) and Hsp90 exert distinct effects on the stability and cell surface levels of native and misfolded forms of the human insulin receptor (hIR) and a human variant found in type A insulin resistance. CRT was unique in stabilizing the disease variant and in augmenting hIR expression when glycolysis was abrogated. Effects of Hsp90 were independent of receptor tyrosine phosphorylation and did not change levels of downstream signaling kinases. Live cell imaging revealed that movement of the hIR through the ER was accelerated by misfolding or by overexpression of either CRT or Hsp90. Together, our results indicate that both CRT and Hsp90 control expression of hIR at its earliest maturation stages and modulate its movement within the ER before either degradation or cell surface expression. PMID:17563366

Ramos, Rowena R.; Swanson, Andrea J.; Bass, Joseph

2007-01-01

164

Calreticulin and Hsp90 stabilize the human insulin receptor and promote its mobility in the endoplasmic reticulum.  

PubMed

Elimination of misfolded membrane proteins in the endoplasmic reticulum (ER) affects cell survival and growth and can be triggered by either local physiologic events or disease-associated mutations. Regulation of signaling receptor degradation involves both cytosolic and ER luminal molecular chaperones, but the mechanisms and timing of this process remain uncertain. Here we report that calreticulin (CRT) and Hsp90 exert distinct effects on the stability and cell surface levels of native and misfolded forms of the human insulin receptor (hIR) and a human variant found in type A insulin resistance. CRT was unique in stabilizing the disease variant and in augmenting hIR expression when glycolysis was abrogated. Effects of Hsp90 were independent of receptor tyrosine phosphorylation and did not change levels of downstream signaling kinases. Live cell imaging revealed that movement of the hIR through the ER was accelerated by misfolding or by overexpression of either CRT or Hsp90. Together, our results indicate that both CRT and Hsp90 control expression of hIR at its earliest maturation stages and modulate its movement within the ER before either degradation or cell surface expression. PMID:17563366

Ramos, Rowena R; Swanson, Andrea J; Bass, Joseph

2007-06-19

165

Abundant accumulation of the calcium-binding molecular chaperone calreticulin in specific floral tissues of Arabidopsis thaliana.  

PubMed Central

Calreticulin (CRT) is a calcium-binding protein in the endoplasmic reticulum (ER) with an established role as a molecular chaper-one. An additional function in signal transduction, specifically in calcium distribution, is suggested but not proven. We have analyzed the expression pattern of Arabidopsis thaliana CRTs for a comparison with these proposed roles. Three CRT genes were expressed, with identities of the encoded proteins ranging from 54 to 86%. Protein motifs with established functions found in CRTs of other species were conserved. CRT was found in all of the cells in low amounts, whereas three distinct floral tissues showed abundant expression: secreting nectaries, ovules early in development, and a set of subepidermal cells near the abaxial surface of the anther. Localization in the developing endosperm, which is characterized by high protein synthesis rates, can be reconciled with a specific chaperone function. Equally, nectar production and secretion, a developmental stage marked by abundant ER, may require abundant CRT to accommodate the traffic of secretory proteins through the ER. Localization of CRT in the anthers, which are degenerating at the time of maximum expression of CRT, cannot easily be reconciled with a chaperone function but may indicate a role for CRT in anther maturation or dehiscence. PMID:9159940

Nelson, D E; Glaunsinger, B; Bohnert, H J

1997-01-01

166

Proteinase 3, the autoantigen in granulomatosis with polyangiitis, associates with calreticulin on apoptotic neutrophils, impairs macrophage phagocytosis, and promotes inflammation.  

PubMed

Proteinase 3 (PR3) is the target of anti-neutrophil cytoplasm Abs in granulomatosis with polyangiitis, a form of systemic vasculitis. Upon neutrophil apoptosis, PR3 is coexternalized with phosphatidylserine and impaired macrophage phagocytosis. Calreticulin (CRT), a protein involved in apoptotic cell recognition, was found to be a new PR3 partner coexpressed with PR3 on the neutrophil plasma membrane during apoptosis, but not after degranulation. The association between PR3 and CRT was demonstrated in neutrophils by confocal microscopy and coimmunoprecipitation. Evidence for a direct interaction between PR3 and the globular domain of CRT, but not with its P domain, was provided by surface plasmon resonance spectroscopy. Phagocytosis of apoptotic neutrophils from healthy donors was decreased after blocking lipoprotein receptor-related protein (LRP), a CRT receptor on macrophages. In contrast, neutrophils from patients with granulomatosis with polyangiitis expressing high membrane PR3 levels showed a lower rate of phagocytosis than those from healthy controls not affected by anti-LRP, suggesting that the LRP-CRT pathway was disturbed by PR3-CRT association. Moreover, phagocytosis of apoptotic PR3-expressing cells potentiated proinflammatory cytokine in vitro by human monocyte-derived macrophages and in vivo by resident murine peritoneal macrophages, and diverted the anti-inflammatory response triggered by the phagocytosis of apoptotic cells after LPS challenge in thioglycolate-elicited murine macrophages. Therefore, membrane PR3 expressed on apoptotic neutrophils might amplify inflammation and promote autoimmunity by affecting the anti-inflammatory "reprogramming" of macrophages. PMID:22844112

Gabillet, Julie; Millet, Arnaud; Pederzoli-Ribeil, Magali; Tacnet-Delorme, Pascale; Guillevin, Loïc; Mouthon, Luc; Frachet, Philippe; Witko-Sarsat, Véronique

2012-09-01

167

Overexpression of calreticulin in pre-eclamptic placentas: effect on apoptosis, cell invasion and severity of pre-eclampsia.  

PubMed

Endoplasmic reticulum (ER) stress has recently been identified as an important process involved in the pathology of pre-eclampsia (PE). Calreticulin (CRT) is an important ER resident protein which participates in the regulation of intracellular Ca(2+) homeostasis, cell adhesion, and cell apoptosis. In order to clarify the role of this protein in normal human pregnancy and in PE, this study has examined the expression of CRT in pre-eclamptic placenta compared with control placenta. The expression of CRT mRNA and protein was elevated in the pre-eclamptic placentas in comparison with control placentas. Furthermore, the expression level was related to the severity of symptoms experienced by PE patients. Therefore, this study aimed to identify the biological characteristics of the CRT gene in trophoblast cells. A CRT-expressing vector was transfected into the JEG-3 human choriocarcinoma cell line. Investigations showed that both proliferation and invasion were inhibited and apoptosis was promoted by CRT expression in JEG-3 cells. These data suggest that augmentation of CRT in the placenta may induce cell apoptosis and impair the invasion of extravillous trophoblast cells, thus leading to shallow placentation in PE. PMID:22415851

Shi, Zhonghua; Hou, Wenwen; Hua, Xiangdong; Zhang, Xiang; Liu, Xiaomei; Wang, Xin; Wang, Xiaoqing

2012-06-01

168

Tumor-specific immunity and antiangiogenesis generated by a DNA vaccine encoding calreticulin linked to a tumor antigen.  

PubMed

Antigen-specific cancer immunotherapy and antiangiogenesis have emerged as two attractive strategies for cancer treatment. An innovative approach that combines both mechanisms will likely generate the most potent antitumor effect. We tested this approach using calreticulin (CRT), which has demonstrated the ability to enhance MHC class I presentation and exhibit an antiangiogenic effect. We explored the linkage of CRT to a model tumor antigen, human papilloma virus type-16 (HPV-16) E7, for the development of a DNA vaccine. We found that C57BL/6 mice vaccinated intradermally with CRT/E7 DNA exhibited a dramatic increase in E7-specific CD8(+) T cell precursors and an impressive antitumor effect against E7-expressing tumors compared with mice vaccinated with wild-type E7 DNA or CRT DNA. Vaccination of CD4/CD8 double-depleted C57BL/6 mice and immunocompromised (BALB/c nu/nu) mice with CRT/E7 DNA or CRT DNA generated significant reduction of lung tumor nodules compared with wild-type E7 DNA, suggesting that antiangiogenesis may have contributed to the antitumor effect. Examination of microvessel density in lung tumor nodules and an in vivo angiogenesis assay further confirmed the antiangiogenic effect generated by CRT/E7 and CRT. Thus, cancer therapy using CRT linked to a tumor antigen holds promise for treating tumors by combining antigen-specific immunotherapy and antiangiogenesis. PMID:11544272

Cheng, W F; Hung, C F; Chai, C Y; Hsu, K F; He, L; Ling, M; Wu, T C

2001-09-01

169

Characterization of DNA vaccines encoding the domains of calreticulin for their ability to elicit tumor-specific immunity and antiangiogenesis.  

PubMed

Antigen-specific cancer immunotherapy and antiangiogenesis are feasible strategies for cancer therapy because they can potentially treat systemic tumors at multiple sites in the body while discriminating between neoplastic and non-neoplastic cells. We have previously developed a DNA vaccine encoding calreticulin (CRT) linked to human papillomavirus-16 E7 and have found that this vaccine generates strong E7-specific antitumor immunity and antiangiogenic effects in vaccinated mice. In this study, we characterized the domains of CRT to produce E7-specific antitumor immunity and antiangiogenic effects by generating DNA vaccines encoding each of the three domains of CRT (N, P, and C domains) linked to the HPV-16 E7 antigen. We found that C57BL/6 mice vaccinated intradermally with DNA encoding the N domain of CRT (NCRT), the P domain of CRT (PCRT), or the C domain of CRT (CCRT) linked with E7 exhibited significant increases in E7-specific CD8(+) T cell precursors and impressive antitumor effects against E7-expressing tumors compared to mice vaccinated with wild-type E7 DNA. In addition, the N domain of CRT also showed antiangiogenic properties that might have contributed to the antitumor effect of NCRT/E7. Thus, the N domain of CRT can be linked to a tumor antigen in a DNA vaccine to generate both antigen-specific immunity and antiangiogenic effects for cancer therapy. PMID:15893626

Cheng, Wen-Fang; Hung, Chien-Fu; Chen, Chi-An; Lee, Chien-Nan; Su, Yi-Ning; Chai, Chee-Yin; Boyd, David A K; Hsieh, Chang-Yao; Wu, T-C

2005-05-31

170

Sindbis virus replicon particles encoding calreticulin linked to a tumor antigen generate long-term tumor-specific immunity.  

PubMed

Alphavirus vectors have emerged as a promising strategy for the development of cancer vaccines and gene therapy applications. In this study, we used the replication-defective vaccine vector SIN replicon particles from a new packaging cell line (PCL) to develop SIN replicon particles encoding calreticulin (CRT) linked to a model tumor antigen, human papillomavirus type 16 (HPV16) E7 protein. The linkage of CRT to E7 in SIN replicon particles resulted in a significant increase in E7-specific CD8(+) T-cell precursors and a strong antitumor effect against E7-expressing tumors in vaccinated mice. SINrep5-CRT/E7 replicon particles enhanced presentation of E7 through the major histocompatibility complex (MHC) class I pathway by infecting dendritic cells (DCs) directly and pulsing DCs with lysates of cells infected by SINrep5-CRT/E7 replicons. Vaccination of immunocompromised (BALB/c nu/nu) mice with SINrep5-CRT/E7 replicon particles also generated significant reduction of lung tumor nodules, suggesting that antiangiogenesis may contribute to the antitumor effect of SINrep5-CRT/E7 replicon particles. Furthermore, SINrep5-CRT/E7 replicon particles generated long-term in vivo tumor protection effects and antigen-specific memory immunities. We concluded that the CRT strategy used in the context of SIN replicon particles facilitated the generation of a highly effective vaccine for cancer prophylaxis and immunotherapy. PMID:16645621

Cheng, W-F; Lee, C-N; Su, Y-N; Chai, C-Y; Chang, M-C; Polo, J M; Hung, C-F; Wu, T-C; Hsieh, C-Y; Chen, C-A

2006-09-01

171

A conserved basic residue cluster is essential for the protein quality control function of the Arabidopsis calreticulin 3  

PubMed Central

Calreticulin (CRT) is a highly conserved chaperone-like lectin that regulates Ca2+ homeostasis and participates in protein quality control in the endoplasmic reticulum (ER). Most of our CRT knowledge came from mammalian studies, but our understanding of plant CRTs is limited. Many plants contain more than two CRTs that form two distinct groups: CRT1/CRT2 and CRT3. Previous studies on plant CRTs were focused on their Ca2+-binding function, but recent studies revealed a crucial role for the Arabidopsis CRT3 in ER retention of a mutant brassinosteroid receptor, brassinosteroid-insensitive 1-9 (bri1-9) and in complete folding of a plant immunity receptor EF-Tu Receptor (EFR). However, little is known about the molecular basis of the functional specification of the CRTs. We have recently shown that the C-terminal domain of CRT3, which is rich in basic residues, is essential for retaining bri1-9 in the ER; however, its role in assisting EFR folding has not been studied. Here, we used an insertional mutant of CRT3, ebs2-8 (EMS mutagenized bri1 suppressor 2-8), in the bri1-9 background as a genetic system to investigate the functional importance of two basic residue clusters in the CRT3?s C-terminal domain. Complementation experiments of ebs2-8 bri1-9 with mutant CRT3M transgenes showed that a highly conserved basic tetrapeptide Arg392Arg393Arg394Lys395 is essential but a less conserved basic tetrapeptide Arg401Arg402Arg403Arg404 is dispensable for the quality control function of CRT3 that retains bri1-9 in the ER and facilitates the complete folding of EFR. PMID:23425854

Liu, Yidan; Li, Jianming

2013-01-01

172

The Ca(2+) status of the endoplasmic reticulum is altered by induction of calreticulin expression in transgenic plants  

NASA Technical Reports Server (NTRS)

To investigate the endoplasmic reticulum (ER) Ca(2+) stores in plant cells, we generated tobacco (Nicotiana tabacum; NT1) suspension cells and Arabidopsis plants with altered levels of calreticulin (CRT), an ER-localized Ca(2+)-binding protein. NT1 cells and Arabidopsis plants were transformed with a maize (Zea mays) CRT gene in both sense and antisense orientations under the control of an Arabidopsis heat shock promoter. ER-enriched membrane fractions from NT1 cells were used to examine how altered expression of CRT affects Ca(2+) uptake and release. We found that a 2.5-fold increase in CRT led to a 2-fold increase in ATP-dependent (45)Ca(2+) accumulation in the ER-enriched fraction compared with heat-shocked wild-type controls. Furthermore, after treatment with the Ca(2+) ionophore ionomycin, ER microsomes from NT1 cells overproducing CRT showed a 2-fold increase in the amount of (45)Ca(2+) released, and a 2- to 3-fold increase in the amount of (45)Ca(2+) retained compared with wild type. These data indicate that altering the production of CRT affects the ER Ca(2+) pool. In addition, CRT transgenic Arabidopsis plants were used to determine if altered CRT levels had any physiological effects. We found that the level of CRT in heat shock-induced CRT transgenic plants correlated positively with the retention of chlorophyll when the plants were transferred from Ca(2+)-containing medium to Ca(2+)-depleted medium. Together these data are consistent with the hypothesis that increasing CRT in the ER increases the ER Ca(2+) stores and thereby enhances the survival of plants grown in low Ca(2+) medium.

Persson, S.; Wyatt, S. E.; Love, J.; Thompson, W. F.; Robertson, D.; Boss, W. F.; Brown, C. S. (Principal Investigator)

2001-01-01

173

Alteration of integrin-dependent adhesion and signaling in EMT-like MDCK cells established through overexpression of calreticulin.  

PubMed

Calreticulin (CRT) is a multi-functional Ca(2+) -binding molecular chaperone in the endoplasmic reticulum. We previously reported that kidney epithelial cell-derived Madin-Darby Canine Kidney cells were transformed into mesenchymal-like cells by gene transfection of CRT. In this study, we investigated the altered characteristics of cell adhesion in these epithelial-mesenchymal transition (EMT)-like cells. Several extracellular matrix substrata were tested, and cell adhesion to fibronectin was found to be specifically increased in the CRT-overexpressing cells compared to controls. The expression of integrins was significantly up-regulated in subunits ?5 and ?V, resulting in an increase in the formation of complexes such as ?5?1 and ?V?3. These integrins also contributed to the enhanced binding of fibronectin. In the CRT-overexpressing cells, the phosphorylation of Akt, a downstream target of integrin-linked kinase (ILK), was up-regulated on attachment to fibronectin or collagen IV. Integrin-associated signaling through ILK was also promoted on attachment to fibronectin, suggesting some of the correlation between ILK and Akt in the CRT-overexpressing cells. Furthermore, on treatment with 1,2-bis (2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid tetra (acetoxymethyl) ester, a membrane-permeable Ca(2+) chelator, the enhanced Akt signaling was suppressed with a concomitant decrease in the formation of complexes between integrins and ILK in the CRT-overexpressing cells. In conclusion, these findings demonstrate that CRT regulates cell-substratum adhesion by modulating integrin-associated signaling through altered Ca(2+) homeostasis in the CRT-overexpressing EMT-like cells, suggesting a novel regulatory role for CRT in EMT. PMID:21557298

Ihara, Yoshito; Inai, Yoko; Ikezaki, Midori

2011-09-01

174

Entamoeba histolytica and E. dispar Calreticulin: Inhibition of Classical Complement Pathway and Differences in the Level of Expression in Amoebic Liver Abscess  

PubMed Central

The role of calreticulin (CRT) in host-parasite interactions has recently become an important area of research. Information about the functions of calreticulin and its relevance to the physiology of Entamoeba parasites is limited. The present work demonstrates that CRT of both pathogenic E. histolytica and nonpathogenic E. dispar species specifically interacted with human C1q inhibiting the activation of the classical complement pathway. Using recombinant EhCRT protein, we demonstrate that CRT interaction site and human C1q is located at the N-terminal region of EhCRT. The immunofluorescence and confocal microscopy experiments show that CRT and human C1q colocalize in the cytoplasmic vesicles and near to the surface membrane of previously permeabilized trophozoites or are incubated with normal human serum which is known to destroy trophozoites. In the presence of peripheral mononuclear blood cells, the distribution of EhCRT and C1q is clearly over the surface membrane of trophozoites. Nevertheless, the level of expression of CRT in situ in lesions of amoebic liver abscess (ALA) in the hamster model is different in both Entamoeba species; this molecule is expressed in higher levels in E. histolytica than in E. dispar. This result suggests that EhCRT may modulate some functions during the early moments of the host-parasite relationship. PMID:24860808

Ximenez, Cecilia; Gonzalez, Enrique; Nieves, Miriam E.; Silva-Olivares, Angelica; Shibayama, Mineko; Galindo-Gomez, Silvia; Escobar-Herrera, Jaime; Garcia de Leon, Ma del Carmen; Moran, Patricia; Valadez, Alicia; Rojas, Liliana; Hernandez, Eric G.; Partida, Oswaldo; Cerritos, Rene

2014-01-01

175

Poly(I:C) treatment influences the expression of calreticulin and profilin-1 in a human HNSCC cell line: a proteomic study.  

PubMed

Polyinosinic:polycytidylic acid (poly (I:C)) has been formerly known to be an interferon inducer but the mechanism of its action was not revealed until the discovery of Toll-like receptors (TLRs). TLRs are members of transmembrane proteins that recognize conserved molecular motifs of viral and bacterial origin and initiate innate immune response. Recent studies have shown that they are also expressed on tumor cells, but their role in these cells is still not clear. TLR3 recognizes double-stranded RNA (poly (I:C)) and is primarily involved in the defense against viruses. TLR3 ligand binding initiates the activation of transcription factors NF-?B, IRF family members, and AP-1, which can induce wide cascading effect on the cell and consequently activate many cellular processes. Since little is known about TLR3 target genes, we have used the proteomic approach to widen the current knowledge. In this study, we have discovered 15 differentially expressed proteins, mostly connected with protein metabolic processes. Furthermore, we have confirmed by Western blot that calreticulin and profilin-1, proteins which have been shown previously to be involved in processes connected with tumor progression, are differentially expressed after poly(I:C) treatment. By using TLR3 small interfering RNA, we showed that calreticulin expression might be TLR3 dependent, unlike profilin-1. PMID:22415225

Matijevi?, Tanja; Paveli?, Jasminka

2012-08-01

176

Recombined DNA vaccines encoding calreticulin linked to HPV6bE7 enhance immune response and inhibit angiogenic activity in B16 melanoma mouse model expressing HPV 6bE7 antigen  

Microsoft Academic Search

Calreticulin (CRT) has been reported to have an effect of upregulating MHC class I presentation as well as inhibiting angiogenesis in vitro and in vivo. Combination of dual mechanisms of enhanced immunogenicity of human papillomavirus (HPV) 6bE7 antigen and antiangiogenesis may be introduced in the strategy of vaccines against condyloma acuminatum (CA) resulting from HPV infection. Therefore, we constructed DNA

Ke-Jia Zhao; Hao Cheng; Ke-Jian Zhu; Yan Xu; Min-li Chen; Xing Zhang; Tao Song; Jun Ye; Qi Wang; Da-Fang Chen

2006-01-01

177

Stau-catalyzed Nuclear Fusion  

E-print Network

We point out that the stau may play a role of a catalyst for nuclear fusions if the stau is a long-lived particle as in the scenario of gravitino dark matter. In this letter, we consider d d fusion under the influence of stau where the fusion is enhanced because of a short distance between the two deuterons. We find that one chain of the d d fusion may release an energy of O(10) GeV per stau. We discuss problems of making the stau-catalyzed nuclear fusion of practical use with the present technology of producing stau.

K. Hamaguchi; T. Hatsuda; T. T. Yanagida

2006-07-24

178

Roles of calreticulin and calnexin during mucin synthesis in LS180 and HT29/A1 human colonic adenocarcinoma cells.  

PubMed Central

Molecular chaperones are presumed to associate with large secretory mucin glycoproteins during their synthesis in the endoplasmic reticulum (ER), but have not been identified to date. We decided to look for possible involvement of the chaperones calreticulin (CRT) and calnexin (CLN) during synthesis of two similar gastrointestinal mucins, MUC2 and MUC5AC. Pulse-chase labelling of MUC2 and MUC5AC with [(35)S]methionine/cysteine ([(35)S]Promix) was performed using LS180 and HT29/A1 colonic carcinoma cell lines and was followed by immunoprecipitation with anti-mucin and anti-chaperone antibodies. The precipitated labelled mucin precursors were analysed by SDS/PAGE and autoradiography. Using antibodies specific for each mucin, newly synthesized monomeric precursors of both MUC2 and MUC5AC were detected after a 15 min pulse and then disappeared as oligomers were formed during a 2 h chase period. Only homo-oligomers of MUC2 and MUC5AC were present in the cells. Using anti-CRT, the MUC2 monomeric precursor and oligomer were co-precipitated from both cell lines after a 15 min pulse and the oligomer less strongly after a 0.5 h chase, but there was little co-precipitation after a 2 h chase. At this time, MUC2 immunoprecipitated by anti-MUC2 was completely oligomerized and was endo-beta-N-acetylglucosaminidase-resistant, indicating that the mucin had reached the Golgi region. MUC2 co-precipitated with CRT at zero time and 0.5 h was endo-beta-N-acetylglucosaminidase-sensitive; therefore CRT must have associated with MUC2 in the ER. Treatment with tunicamycin (TUN) diminished the binding of MUC2 to CRT, suggesting a requirement for initial N-glycan addition during this process. Using anti-CLN, only a weak co-precipitation of MUC2, compared with that seen with anti-CRT, was detected in LS180 cells. In contrast with the findings for MUC2, there was no co-precipitation of MUC5AC with CRT or CLN from either cell line at the various time points. In conclusion, CRT and CLN appear to be involved in MUC2 synthesis at the stage of folding and oligomerization in the ER. Since no interaction of the chaperones with MUC5AC was detected at a similar stage of synthesis, these two structurally similar secretory mucins seem to have different chaperone requirements in the ER. PMID:10417322

McCool, D J; Okada, Y; Forstner, J F; Forstner, G G

1999-01-01

179

Calreticulin mediated glucocorticoid receptor export is involved in beta-catenin translocation and Wnt signalling inhibition in human osteoblastic cells.  

PubMed

Wnt signalling pathway is a multicomponent cascade involving interaction of several proteins and found to be important for development and function of various cells and tissues. There is increasing evidence that the Wnt/beta-catenin pathway constitutes also one of the essential molecular mechanisms controlling the metabolic aspects of osteoblastic cells. However, in bone, glucocorticoids (GCs) have been reported to weaken Wnt signalling. Therefore, the aim of this study was to characterize the mechanisms behind the cross-talk of these two signalling pathways in human osteoblastic cells. Based on our findings, liganded glucocorticoid receptor (GR) modulated Wnt signalling pathway by decreasing beta-catenin's nuclear accumulation and increasing its relocalization to cell membranes rather than affecting its degradation in human osteoblastic cells. The region of GR responsible for this inhibitory effect located into an area, which harbours the DNA binding as well as nuclear export domains. In further studies, a chaperone protein calreticulin (CRT), known to bind the DNA binding domain of GR and regulate receptor export, was found to be involved in the GR-mediated downregulation of Wnt signalling: GR mutants containing incomplete CRT binding sites were not able to translocate beta-catenin to cell surface. In addition, the inhibitory effect of GCs on endogenous Wnt target gene, cyclin D1, was abolished, when the expression of CRT was attenuated by the RNAi technique. Furthermore, GR and beta-catenin were shown to exist in the same immunocomplex, while interaction between CRT and beta-catenin was observed only in the presence of GR as a mediator molecule. In addition, the GR mutant lacking CRT binding ability impaired the complex formation between beta-catenin and CRT. Together with GR, beta-catenin could thus be co-transported from the nucleus in a CRT-dependent way. These observations represent a novel mechanism for GCs to downregulate Wnt signalling pathway in human osteoblastic cells. Knowledge of these molecular mechanisms is important for understanding the network of multiple signalling cascades in bone environment. Functional Wnt signalling pathway is a prerequisite for proper osteoblastogenesis, and this modulative cross-talk between the steroid pathway and Wnt cascade could therefore explain some of the two-edged effects of GCs on osteoblastic differentiation and function. PMID:19100874

Olkku, Anu; Mahonen, Anitta

2009-04-01

180

Cold fusion catalyzed by muons and electrons  

Microsoft Academic Search

Two alternative methods have been suggested to produce fusion power at low temperature. The first, muon catalyzed fusion or MCF, uses muons to spontaneously catalyze fusion through the muon mesomolecule formation. Unfortunately, this method fails to generate enough fusion energy to supply the muons, by a factor of about ten. The physics of MCF is discussed, and a possible approach

Kulsrud

1990-01-01

181

Selective Oxidations Catalyzed by Chloroperoxidase (Selectieve Oxidaties Gekatalyseerd door Chloorperoxidase).  

National Technical Information Service (NTIS)

Content: Introduction; Selective oxidations catalyzed by peroxidases; Chloroperoxidase catalyzed sulfoxidations in tert-butyl alcohol/water mixtures; Synthesis of substituted oxindoles by chloroperoxidase catalyzed oxidation of indoles; Chloroperoxidase c...

M. P. J. van Deurzen

1996-01-01

182

Ectopic expression of a maize calreticulin mitigates calcium deficiency-like disorders in sCAX1-expressing tobacco and tomato.  

PubMed

Deregulated expression of an Arabidopsis H?/Ca²? antiporter (sCAX1) in agricultural crops increases total calcium (Ca²?) but may result in yield losses due to Ca²? deficiency-like symptoms. Here we demonstrate that co-expression of a maize calreticulin (CRT, a Ca²? binding protein located at endoplasmic reticulum) in sCAX1-expressing tobacco and tomato plants mitigated these adverse effects while maintaining enhanced Ca²? content. Co-expression of CRT and sCAX1 could alleviate the hypersensitivity to ion imbalance in tobacco plants. Furthermore, blossom-end rot (BER) in tomato may be linked to changes in CAX activity and enhanced CRT expression mitigated BER in sCAX1 expressing lines. These findings suggest that co-expressing Ca²? transporters and binding proteins at different intracellular compartments can alter the content and distribution of Ca²? within the plant matrix. PMID:23007728

Wu, Qingyu; Shigaki, Toshiro; Han, Jeung-Sul; Kim, Chang Kil; Hirschi, Kendal D; Park, Sunghun

2012-12-01

183

Wogonin Induced Calreticulin/Annexin A1 Exposure Dictates the Immunogenicity of Cancer Cells in a PERK/AKT Dependent Manner  

PubMed Central

In response to ionizing irradiation and certain chemotherapeutic agents, dying tumor cells elicit a potent anticancer immune response. However, the potential effect of wogonin (5,7-dihydroxy-8-methoxyflavone) on cancer immunogenicity has not been studied. Here we demonstrated for the first time that wogonin elicits a potent antitumor immunity effect by inducing the translocation of calreticulin (CRT) and Annexin A1 to cell plasma membrane as well as the release of high-mobility group protein 1 (HMGB1) and ATP. Signal pathways involved in this process were studied. We found that wogonin-induced reactive oxygen species (ROS) production causes an endoplasmic reticulum (ER) stress response, including the phosphorylation of PERK (PKR-like endoplasmic reticulum kinase)/PKR (protein kinase R) and eIF2? (eukaryotic initiation factor 2?), which served as upstream signal for the activation of phosphoinositide 3-kinase (PI3K)/AKT, inducing calreticulin (CRT)/Annexin A1 cell membrane translocation. P22/CHP, a Ca2+-binding protein, was associated with CRT and was required for CRT translocation to cell membrane. The releases of HMGB1 and ATP from wogonin treated MFC cells, alone or together with other possible factors, activated dendritic cells and induced cytokine releases. In vivo study confirmed that immunization with wogonin-pretreated tumor cells vaccination significantly inhibited homoplastic grafted gastric tumor growth in mice and a possible inflammatory response was involved. In conclusion, the activation of PI3K pathway elicited by ER stress induced CRT/Annexin A1 translocation (“eat me” signal) and HMGB1 release, mediating wogonin-induced immunity of tumor cell vaccine. This indicated that wogonin is a novel effective candidate of immunotherapy against gastric tumor. PMID:23251389

Yang, Yong; Li, Xian-Jing; Chen, Zhen; Zhu, Xuan-Xuan; Wang, Jing; Zhang, Lin-bo; Qiang, Lei; Ma, Yan-jun; Li, Zhi-yu; Guo, Qing-Long; You, Qi-Dong

2012-01-01

184

Wogonin induced calreticulin/annexin A1 exposure dictates the immunogenicity of cancer cells in a PERK/AKT dependent manner.  

PubMed

In response to ionizing irradiation and certain chemotherapeutic agents, dying tumor cells elicit a potent anticancer immune response. However, the potential effect of wogonin (5,7-dihydroxy-8-methoxyflavone) on cancer immunogenicity has not been studied. Here we demonstrated for the first time that wogonin elicits a potent antitumor immunity effect by inducing the translocation of calreticulin (CRT) and Annexin A1 to cell plasma membrane as well as the release of high-mobility group protein 1 (HMGB1) and ATP. Signal pathways involved in this process were studied. We found that wogonin-induced reactive oxygen species (ROS) production causes an endoplasmic reticulum (ER) stress response, including the phosphorylation of PERK (PKR-like endoplasmic reticulum kinase)/PKR (protein kinase R) and eIF2? (eukaryotic initiation factor 2?), which served as upstream signal for the activation of phosphoinositide 3-kinase (PI3K)/AKT, inducing calreticulin (CRT)/Annexin A1 cell membrane translocation. P22/CHP, a Ca(2+)-binding protein, was associated with CRT and was required for CRT translocation to cell membrane. The releases of HMGB1 and ATP from wogonin treated MFC cells, alone or together with other possible factors, activated dendritic cells and induced cytokine releases. In vivo study confirmed that immunization with wogonin-pretreated tumor cells vaccination significantly inhibited homoplastic grafted gastric tumor growth in mice and a possible inflammatory response was involved. In conclusion, the activation of PI3K pathway elicited by ER stress induced CRT/Annexin A1 translocation ("eat me" signal) and HMGB1 release, mediating wogonin-induced immunity of tumor cell vaccine. This indicated that wogonin is a novel effective candidate of immunotherapy against gastric tumor. PMID:23251389

Yang, Yong; Li, Xian-Jing; Chen, Zhen; Zhu, Xuan-Xuan; Wang, Jing; Zhang, Lin-bo; Qiang, Lei; Ma, Yan-Jun; Li, Zhi-yu; Guo, Qing-Long; You, Qi-Dong

2012-01-01

185

Transition metal-catalyzed functionalization of pyrazines.  

PubMed

Transition metal-catalyzed reactions are generally used for carbon-carbon bond formation on pyrazines and include, but are not limited to, classical palladium-catalyzed reactions like Sonogashira, Heck, Suzuki, and Stille reactions. Also a few examples of carbon-heteroatom bond formation in pyrazines are known. This perspective reviews recent progress in the field of transition metal-catalyzed cross-coupling reactions on pyrazine systems. It deals with the most important C-C- and C-X-bond formation methodologies. PMID:23632914

Nikishkin, Nicolai I; Huskens, Jurriaan; Verboom, Willem

2013-06-14

186

Copper-Catalyzed Trifluoromethylation of Unactivated Olefins  

E-print Network

Activating the inactive: A copper-catalyzed allylic trifluoromethylation of unactivated terminal olefins proceeds under mild conditions to produce linear allylic trifluoromethylated products with high E/Z selectivity (see ...

Parsons, Andrew T.

187

Manganese-catalyzed carbonylation of alkyl iodides  

E-print Network

The palladium-catalyzed cross-coupling of aryl bromides with zirconocene-benzyne complexes has been investigated by S.L. Buchwald and coworkers. This method allows the formation of substituted biphenyls and terphenyls, ...

Westerhaus, Felix Alexander

2009-01-01

188

Catalyzing innovations for sustainable chemicals & fuels  

E-print Network

Catalyzing innovations for sustainable chemicals & fuels Annual Report 2013-2014 #12;a unique!on and the Environmental Protec!on Agency, creates a network for designing sustainable chemicals. A successful renewal

189

Palladium(0)-Catalyzed Arylative Dearomatization of Phenols  

E-print Network

The palladium-catalyzed arylative dearomatization of phenols to yield spirocyclohexadienone products in good to excellent yields has been developed. Preliminary results demonstrate that the formation of the spirocyclic ...

Rousseaux, Sophie

190

Advances in lipase-catalyzed esterification reactions.  

PubMed

Lipase-catalyzed esterification reactions are among the most significant chemical and biochemical processes of industrial relevance. Lipases catalyze hydrolysis as well as esterification reactions. Enzyme-catalyzed esterification has acquired increasing attention in many applications, due to the significance of the derived products. More specifically, the lipase-catalyzed esterification reactions attracted research interest during the past decade, due to an increased use of organic esters in biotechnology and the chemical industry. Lipases, as hydrolyzing agents are active in environments, which contain a minimum of two distinct phases, where all reactants are partitioned between these phases, although their distribution is not fixed and changes as the reaction proceeds. The kinetics of the lipase-catalyzed reactions is governed by a number of factors. This article presents a thorough and descriptive evaluation of the applied trends and perspectives concerning the enzymatic esterification, mainly for biofuel production; an emphasis is given on essential factors, which affect the lipase-catalyzed esterification reaction. Moreover, the art of using bacterial and/or fungal strains for whole cell biocatalysis purposes, as well as carrying out catalysis by various forms of purified lipases from bacterial and fungal sources is also reviewed. PMID:23954307

Stergiou, Panagiota-Yiolanda; Foukis, Athanasios; Filippou, Michalis; Koukouritaki, Maria; Parapouli, Maria; Theodorou, Leonidas G; Hatziloukas, Efstathios; Afendra, Amalia; Pandey, Ashok; Papamichael, Emmanuel M

2013-12-01

191

Rh-catalyzed linear hydroformylation of styrene.  

PubMed

Usually the Rh-catalyzed hydroformylation of styrene predominantly yields the branched, chiral aldehyde. An inversion of regioselectivity can be achieved using strong ?-acceptor ligands. Binaphthol-based diphosphite and bis(dipyrrolyl-phosphorodiamidite) ligands were applied in the Rh-catalyzed hydroformylation of styrene. High selectivities up to 83% of 3-phenylpropanal were obtained with 1,1-bi-2-naphthol-based bis(dipyrrolyl-phosphorodiamidite) with virtually no hydrogenation to ethyl benzene. The coordination chemistry of those ligands towards Rh(I) was investigated spectroscopically and structurally. PMID:23104326

Boymans, Evert; Janssen, Michèle; Müller, Christian; Lutz, Martin; Vogt, Dieter

2013-01-01

192

Oligonucleotide formation catalyzed by mononucleotide matrices  

NASA Technical Reports Server (NTRS)

Pb(2+)-containing precipitates of mononucleotides form matrices which catalyze the self-condensation of nucleotide 5-prime-phosphorimidazolides and their condensation with nucleosides. The reactions exhibit base-pairing specificity between matrix nucleotide and substrate, and usually follow the Watson-Crick pairing rules. Although purine polynucleotides do not facilitate the oligomerization of pyrimidine nucleotide monomers in solution, it is interesting that purine-containing matrices do catalyze such a reaction. The significance of the results in the context of the prebiotic evolution of polynucleotides is discussed.

Lohrmann, R.

1982-01-01

193

Transition metal catalyzed borylation of functional ?-systems  

PubMed Central

Borylated functional ?-systems are useful building blocks to enable efficient synthesis of novel molecular architectures with beautiful structures, intriguing properties and unique functions. Introduction of boronic ester substituents to a variety of extended ?-systems can be achieved through either iridium-catalyzed direct C–H borylation or the two-step procedure via electrophilic halogenation followed by palladium-catalyzed borylation. This review article focuses on our recent progress on borylation of large ?-conjugated systems such as porphyrins, perylene bisimides, hexabenzocoronenes and dipyrrins. PMID:24492644

SHINOKUBO, Hiroshi

2014-01-01

194

Attractor Explosions and Catalyzed Vacuum Decay  

E-print Network

We present a mechanism for catalyzed vacuum bubble production obtained by combining moduli stabilization with a generalized attractor phenomenon in which moduli are sourced by compact objects. This leads straightforwardly to a class of examples in which the Hawking decay process for black holes unveils a bubble of a different vacuum from the ambient one, generalizing the new endpoint for Hawking evaporation discovered recently by Horowitz. Catalyzed vacuum bubble production can occur for both charged and uncharged bodies, including Schwarzschild black holes for which massive particles produced in the Hawking process can trigger vacuum decay. We briefly discuss applications of this process to the population and stability of metastable vacua.

Daniel Green; Eva Silverstein; David Starr

2006-05-04

195

Iron Catalyzed Asymmetric Oxyamination of Olefins  

PubMed Central

The regioselective and enantioselective oxyamination of alkenes with N-sulfonyl oxaziridines is catalyzed by a novel iron(II) bis(oxazoline) complex. This process affords oxazolidine products that can be easily manipulated to yield highly enantioenriched free amino alcohols. The regioselectivity of this process is complementary to that obtained from the analogous copper(II)-catalyzed reaction. Thus, both regioisomers of enantioenriched 1,2-aminoalcohols can be obtained using oxaziridine-mediated oxyamination reactions, and the overall sense of regiochemistry can be controlled using the appropriate choice of inexpensive first-row transition metal catalyst. PMID:22793789

Williamson, Kevin S.; Yoon, Tehshik P.

2012-01-01

196

A calreticulin/gC1qR complex prevents cells from dying: a conserved mechanism from arthropods to humans.  

PubMed

The crossroad between cell death and proliferation is a general target for viral infections because viruses need to obstruct apoptosis to use cells for their own replication. Inducing immunogenic cell death in proliferating cells is also an important aim of anticancer chemotherapy. The C1q-binding proteins calreticulin (CRT) and gC1qR are highly conserved ubiquitous proteins, which are putative targets for viral manipulation and are associated with cancer. Here we show that these proteins form a complex in the cytoplasm as a response to viral infection resulting in apoptosis prevention. The formation of a cytosolic CRT/gC1qR complex prevents cell death by reducing gC1qR translocation into the mitochondria, and we provide evidence that this mechanism is conserved from arthropods to human cancer cells. Furthermore, we show that it is possible to prevent this complex from being formed in cancer cells. When the peptides of the complex proteins are overexpressed in these cells, the cells undergo apoptosis. This finding shows a causal link between virus and cancer and may be used to develop new tools in anticancer or antiviral therapy. PMID:23378602

Watthanasurorot, Apiruck; Jiravanichpaisal, Pikul; Söderhäll, Kenneth; Söderhäll, Irene

2013-04-01

197

N-linked oligosaccharide processing, but not association with calnexin/calreticulin is highly correlated with endoplasmic reticulum-associated degradation of antithrombin Glu313-deleted mutant.  

PubMed

Previously we showed that two antithrombin mutants were degraded through an endoplasmic reticulum (ER)-associated degradation (ERAD) pathway [F. Tokunaga et al., FEBS Lett. 412 (1997) 65]. Here, we examined the combined effects of inhibitors of glycosidases, protein synthesis, proteasome, and tyrosine phosphatase on ERAD of a Glu313-deleted (DeltaGlu) mutant of antithrombin. We found that kifunensine, an ER mannosidase I inhibitor, suppressed ERAD, indicating that specific mannose trimming plays a critical role. Cycloheximide and puromycin, inhibitors of protein synthesis, also suppressed ERAD, the effects being cancelled by pretreatment with castanospermine. In contrast, kifunensine suppressed ERAD even in castanospermine-treated cells, suggesting that suppression of ERAD does not always require the binding of lectin-like ER chaperones-like calnexin and/or calreticulin. These results indicate that, besides proteasome inhibitors, inhibitors of ER mannosidase I and protein synthesis suppress ERAD of the antithrombin deltaGlu mutant at different stages, and processing of N-linked oligosaccharides highly correlated with the efficiency of ERAD. PMID:12623072

Tokunaga, Fuminori; Hara, Kazuya; Koide, Takehiko

2003-03-15

198

Soluble calreticulin induces tumor necrosis factor-? (TNF-?) and interleukin (IL)-6 production by macrophages through mitogen-activated protein kinase (MAPK) and NF?B signaling pathways.  

PubMed

We have recently reported that soluble calreticulin (CRT) accumulates in the sera of patients with rheumatoid arthritis or systemic lupus erythematosus. Moreover, following self-oligomerization, soluble recombinant CRT (rCRT) polypeptides exhibit potent immunostimulatory activities including macrophage activation in vitro and antibody induction in vivo. This study was designed to further investigate the underlying molecular mechanisms for soluble CRT-induced macrophage activation. Treatment of murine macrophages with oligomerized rCRT (OrCRT) led to (i) TNF-? and IL-6 transcription and protein expression without affecting intracellular mRNA stability; and (ii) I?B? degradation, NF?B phosphorylation and sustained MAPK phosphorylation in cells. Inhibition of IKK and JNK in macrophages substantially abrogated production of TNF-? and IL-6 induced by OrCRT, while ERK suppression only reduced IL-6 expression in parallel experiments. In vitro, fucoidan, a scavenger receptor A (SRA)-specific ligand, significantly reduced the uptake of FITC-labeled OrCRT by macrophages and subsequent MAPK and NF?B activation, thereby suggesting SRA as one of the potential cell surface receptors for soluble CRT. Together, these data indicate that soluble CRT in oligomerized form could play a pathogenic role in autoimmune diseases through induction of pro-inflammatory cytokines (e.g., TNF-? and IL-6) by macrophages via MAPK-NF?B signaling pathway. PMID:24566135

Duo, Cui-Cui; Gong, Fang-Yuan; He, Xiao-Yan; Li, Yan-Mei; Wang, Jun; Zhang, Jin-Ping; Gao, Xiao-Ming

2014-01-01

199

Soluble Calreticulin Induces Tumor Necrosis Factor-? (TNF-?) and Interleukin (IL)-6 Production by Macrophages through Mitogen-Activated Protein Kinase (MAPK) and NF?B Signaling Pathways  

PubMed Central

We have recently reported that soluble calreticulin (CRT) accumulates in the sera of patients with rheumatoid arthritis or systemic lupus erythematosus. Moreover, following self-oligomerization, soluble recombinant CRT (rCRT) polypeptides exhibit potent immunostimulatory activities including macrophage activation in vitro and antibody induction in vivo. This study was designed to further investigate the underlying molecular mechanisms for soluble CRT-induced macrophage activation. Treatment of murine macrophages with oligomerized rCRT (OrCRT) led to (i) TNF-? and IL-6 transcription and protein expression without affecting intracellular mRNA stability; and (ii) I?B? degradation, NF?B phosphorylation and sustained MAPK phosphorylation in cells. Inhibition of IKK and JNK in macrophages substantially abrogated production of TNF-? and IL-6 induced by OrCRT, while ERK suppression only reduced IL-6 expression in parallel experiments. In vitro, fucoidan, a scavenger receptor A (SRA)-specific ligand, significantly reduced the uptake of FITC-labeled OrCRT by macrophages and subsequent MAPK and NF?B activation, thereby suggesting SRA as one of the potential cell surface receptors for soluble CRT. Together, these data indicate that soluble CRT in oligomerized form could play a pathogenic role in autoimmune diseases through induction of pro-inflammatory cytokines (e.g., TNF-? and IL-6) by macrophages via MAPK-NF?B signaling pathway. PMID:24566135

Duo, Cui-Cui; Gong, Fang-Yuan; He, Xiao-Yan; Li, Yan-Mei; Wang, Jun; Zhang, Jin-Ping; Gao, Xiao-Ming

2014-01-01

200

Changes in Tumor Growth and Metastatic Capacities of J82 Human Bladder Cancer Cells Suppressed by Down-Regulation of Calreticulin Expression  

PubMed Central

Bladder cancer is a common urothelial cancer. Through proteomic approaches, calreticulin (CRT) was identified and proposed as a urinary marker for bladder cancer. CRT is a multifunctional molecular chaperone that regulates various cellular functions such as Ca2+ homeostasis and cell adhesion. CRT is overexpressed in various cancers, but its mechanism of action in the development of bladder tumors remains unclear. We generated J82 bladder cancer cells lines that either stably overexpressed or knocked down CRT to investigate the physiological effects of CRT on bladder tumors. Compared with the transfected control vector cells, the knockdown of CRT suppressed cell proliferation, migration, and attachment, whereas overexpression of CRT enhanced cell migration and attachment. We further demonstrated that the phosphorylation status of focal adhesion kinase and paxillin, important regulators of the focal adhesion complex, was also regulated in these cells. In contrast, phosphorylation of Src, a protein tyrosine kinase reported to be affected by CRT, was not significantly different between the control and CRT-RNAi groups. Most importantly, we observed that tumors derived from J82 CRT-RNAi cells were significantly smaller and had fewer metastatic sites in the lung and liver in vivo than did transfected control vector cells. In conclusion, our results suggest that alteration of CRT expression levels might affect bladder cancer progression in vitro and in vivo. PMID:21723245

Lu, Yi-Chien; Chen, Chiung-Nien; Wang, Bojeng; Hsu, Wen-Ming; Chen, Szu-Ta; Chang, King-Jen; Chang, Cheng-Chi; Lee, Hsinyu

2011-01-01

201

Additive effect of calreticulin and translation initiation factor eIF4E on secreted protein production in the baculovirus expression system.  

PubMed

The baculovirus expression vector system is widely used for the production of recombinant proteins. However, the yield of membrane-bound or secreted proteins is relatively low when compared with intracellular or nuclear proteins. In a previous study, we had demonstrated that the co-expression of the human chaperones calreticulin (CALR) or ?-synuclein (?-syn) increased the production of a secreted protein considerably. A similar effect was also seen when co-expressing insect translation initiation factor eIF4E. In this study, different combinations of the three genes were tested (CALR alone, ?-syn?+?CALR, or ?-syn?+?CALR?+?eIF4E) to further improve secretory protein production by assessing the expression level of a recombinant secreted alkaline phosphatase (SEFP). An additional 1.8-fold increment of SEFP production was obtained when cells co-expressed all the three "helper" genes, compared to cells, in which only CALR was co-produced with SEFP. Moreover, the duration of the SEFP production lasted much longer in cells that co-expressed these three "helper" genes, up to 10 dpi was observed. Utilization of this "triple-supporters" containing vector offers significant advantages when producing secreted proteins and is likely to have benefits for the production of viral vaccines and other pharmaceutical products. PMID:23900798

Teng, Chao-Yi; van Oers, Monique M; Wu, Tzong-Yuan

2013-10-01

202

Enhanced protein secretion from insect cells by co-expression of the chaperone calreticulin and translation initiation factor eIF4E.  

PubMed

Host protein synthesis is shut down in the lytic baculovirus expression vector system (BEVS). This also affects host proteins involved in routing secretory proteins through the endoplasmic reticulum (ER)-Golgi system. It has been demonstrated that a secretory alkaline phosphatase-EGFP fusion protein (SEFP) can act as a traceable and sensitive secretory reporter protein in BEVS. In this study, a chaperone, calreticulin (CALR), and the translation initiation factor eIF4E were co-expressed with SEFP using a bicistronic baculovirus expression vector. We observed that the intracellular distribution of SEFP in cells co-expressing CALR was different from co-expressing eIF4E. The increased green fluorescence emitted by cells co-expressing CALR had a good correlation with the abundance of intracellular SEFP protein and an unconventional ER expansion. Cells co-expressing eIF4E, on the other hand, showed an increase in extracellular SEAP activity compared to the control. Utilization of these baculovirus expression constructs containing either eIF4E or CALR offers a significant advantage for producing secreted proteins for various biotechnological and therapeutic applications. PMID:22555850

Teng, Chao-Yi; Chang, Shou-Lin; van Oers, Monique M; Wu, Tzong-Yuan

2013-05-01

203

Adjuvanticity of a recombinant calreticulin fragment in assisting anti-?-glucan IgG responses in T cell-deficient mice.  

PubMed

Polysaccharide-encapsulated fungi are the chief source of diseases in immunocompromised hosts such as those infected with human immunodeficiency virus or neutropenia patients. Currently available polysaccharide-protein conjugate vaccines are mainly T cell dependent and are usually ineffective in weakened immune systems. In this study, laminarin, a well-characterized ?-1,3-glucan, was conjugated with a prokaryotically expressed recombinant fragment (amino acids [aa] 39 to 272) of calreticulin (rCRT/39-272), which exhibits extraordinarily potent immunogenicity and adjuvanticity in experimental animals. The resultant conjugate reserves the immunostimulatory effect of rCRT/39-272 on naïve murine B cells and is capable of eliciting anti-?-glucan IgG (mostly IgG1) responses in not only BALB/c mice but also athymic nude mice. Laminarin-CRT-induced mouse antibodies (Abs) are able to bind with Candida albicans and inhibit its growth in vitro. In addition, vaccination with laminarin-CRT partially protects mice from lethal C. albicans challenge. These results imply that rCRT/39-272 could be used as an ideal carrier or adjuvant for carbohydrate vaccines aimed at inducing or boosting IgG responses to fungal infections in immunodeficient hosts. PMID:23408527

Li, Wei-Ji; Long, Kai; Dong, Hong-Liang; Gao, Xiao-Ming

2013-04-01

204

The n3-polyunsaturated fatty acid docosahexaenoic acid induces immunogenic cell death in human cancer cell lines via pre-apoptotic calreticulin exposure.  

PubMed

Some anticancer chemotherapeutics, such as anthracyclines and oxaliplatin, elicit immunogenic apoptosis, meaning that dying cancer cells are engulfed by dendritic cells and tumor antigens are efficiently presented to CD8+ T cells, which control residual tumor cells. Immunogenic apoptosis is characterized by pre-apoptotic cell surface exposure of calreticulin (CRT), which usually resides into the endoplasmic reticulum. We investigated the ability of the n3-polyunsaturated fatty acid docosahexaenoic acid (22:6n3, DHA) to induce pre-apoptotic CRT exposure on the surface of the human PaCa-44 pancreatic and EJ bladder cancer cell lines. Cells were treated with 150 ?M DHA for different time periods, and, by immunoblot and immunofluorescence, we showed that DHA induced CRT exposure, before the apoptosis-associated phosphatidylserine exposure. As for the known immunogenic compounds, CRT exposure was inhibited by the antioxidant GSH, the pan-caspase zVAD-FMK, and caspase-8 IETD-FMK inhibitor. We provide the first evidence that DHA induces CRT exposure, representing thus a novel potential anticancer immunogenic chemotherapeutic agent. PMID:21779875

Molinari, Romina; D'Eliseo, Donatella; Manzi, Laura; Zolla, Lello; Velotti, Francesca; Merendino, Nicolò

2011-10-01

205

Zeolite 5A Catalyzed Etherification of Diphenylmethanol  

ERIC Educational Resources Information Center

An experiment for the synthetic undergraduate laboratory is described in which zeolite 5A catalyzes the room temperature dehydration of diphenylmethanol, (C[subscript 6]H[subscript 5])[subscript 2]CHOH, producing 1,1,1',1'-tetraphenyldimethyl ether, (C[subscript 6]H[subscript 5])[subscript 2]CHOCH(C[subscript 6]H[subscript 5])[subscript 2]. The…

Cooke, Jason; Henderson, Eric J.; Lightbody, Owen C.

2009-01-01

206

Data, Leadership, and Catalyzing Culture Change  

ERIC Educational Resources Information Center

It is crucial to understand today's tenure-track workers so that colleges and universities can continue to attract and retain a large subset of them by understanding and supporting their satisfaction and success at work. In this article, the authors talk about data, leadership, and catalyzing culture change. They discuss data use in the academy…

Benson, R. Todd; Trower, Cathy A.

2012-01-01

207

Antibody-Catalyzed Degradation of Cocaine  

Microsoft Academic Search

Immunization with a phosphonate monoester transition-state analog of cocaine provided monoclonal antibodies capable of catalyzing the hydrolysis of the cocaine benzoyl ester group. An assay for the degradation of radiolabeled cocaine identified active enzymes. Benzoyl esterolysis yields ecgonine methyl ester and benzoic acid, fragments devoid of cocaine's stimulant activity. Passive immunization with such an artificial enzyme could provide a treatment

Donald W. Landry; Kang Zhao; Ginger X.-Q. Yang; Michael Glickman; Taxiarchis M. Georgiadis

1993-01-01

208

Microorganisms detected by enzyme-catalyzed reaction  

NASA Technical Reports Server (NTRS)

Enzymes detect the presence of microorganisms in soils. The enzyme lysozymi is used to release the enzyme catalase from the microorganisms in a soil sample. The catalase catalyzes the decomposition of added hydrogen peroxide to produce oxygen which is detected manometrically. The partial pressure of the oxygen serves as an index of the samples bacteria content.

Vango, S. P.; Weetall, H. H.; Weliky, N.

1966-01-01

209

Catalyzing innovations for sustainable chemicals & fuels for  

E-print Network

2013 2003 2012 2011 2010 2009 2004 2005 2006 2007 2008 years Catalyzing innovations for sustainable chemicals & fuels for Annual Report 2012-2013 #12;a unique resource for industrial catalysis contents(CEBC)bringstogetherchemistsandchemical engineerstodevelopcleanerandmoreefficient processes for making fuels and chemicals from bothtraditionalandrenewablefeedstocks

210

Organic acids tunably catalyze carbonic acid decomposition.  

PubMed

Density functional theory calculations predict that the gas-phase decomposition of carbonic acid, a high-energy, 1,3-hydrogen atom transfer reaction, can be catalyzed by a monocarboxylic acid or a dicarboxylic acid, including carbonic acid itself. Carboxylic acids are found to be more effective catalysts than water. Among the carboxylic acids, the monocarboxylic acids outperform the dicarboxylic ones wherein the presence of an intramolecular hydrogen bond hampers the hydrogen transfer. Further, the calculations reveal a direct correlation between the catalytic activity of a monocarboxylic acid and its pKa, in contrast to prior assumptions about carboxylic-acid-catalyzed hydrogen-transfer reactions. The catalytic efficacy of a dicarboxylic acid, on the other hand, is significantly affected by the strength of an intramolecular hydrogen bond. Transition-state theory estimates indicate that effective rate constants for the acid-catalyzed decomposition are four orders-of-magnitude larger than those for the water-catalyzed reaction. These results offer new insights into the determinants of general acid catalysis with potentially broad implications. PMID:24933150

Kumar, Manoj; Busch, Daryle H; Subramaniam, Bala; Thompson, Ward H

2014-07-10

211

Lipase catalyzed formation of flavour esters  

Microsoft Academic Search

Summary Thirteen commercial lipase preparations were checked for their ability to catalyse the formation of flavour esters (isoamyl or geranyl acetate, propionate and butyrate) by either direct esterification or ester solvolysis in n-heptane. The formation of isoamyl or geranyl butyrates and propionates by direct esterification was catalyzed by the majority of the tested lipases. Acetic acid esters were more difficult

G. Langrand; C. Triantaphylides; J. Baratti

1988-01-01

212

DNA-catalyzed lysine side chain modification.  

PubMed

Catalyzing the covalent modification of aliphatic amino groups, such as the lysine (Lys) side chain, by nucleic acids has been challenging to achieve. Such catalysis will be valuable, for example, for the practical preparation of Lys-modified proteins. We previously reported the DNA-catalyzed modification of the tyrosine and serine hydroxy side chains, but Lys modification has been elusive. Herein, we show that increasing the reactivity of the electrophilic reaction partner by using 5'-phosphorimidazolide (5'-Imp) rather than 5'-triphosphate (5'-ppp) enables the DNA-catalyzed modification of Lys in a DNA-anchored peptide substrate. The DNA-catalyzed reaction of Lys with 5'-Imp is observed in an architecture in which the nucleophile and electrophile are not preorganized. In contrast, previous efforts showed that catalysis was not observed when Lys and 5'-ppp were used in a preorganized arrangement. Therefore, substrate reactivity is more important than preorganization in this context. These findings will assist ongoing efforts to identify DNA catalysts for reactions of protein substrates at lysine side chains. PMID:24981820

Brandsen, Benjamin M; Velez, Tania E; Sachdeva, Amit; Ibrahim, Nora A; Silverman, Scott K

2014-08-18

213

Isopeptide Ligation Catalyzed by Quintessential Sortase A  

PubMed Central

The housekeeping transpeptidase sortase A (SrtA) from Staphyloccocus aureus catalyzes the covalent anchoring of surface proteins to the cell wall by linking the threonyl carboxylate of the LPXTG recognition motif to the amino group of the pentaglycine cross-bridge of the peptidoglycan. SrtA-catalyzed ligation of an LPXTG containing polypeptide with an aminoglycine-terminated moiety occurs efficiently in vitro and has inspired the use of this enzyme as a synthetic tool in biological chemistry. Here we demonstrate the propensity of SrtA to catalyze “isopeptide” ligation. Using model peptide sequences, we show that SrtA can transfer LPXTG peptide substrates to the ?-amine of specific Lys residues and form cyclized and/or a gamut of branched oligomers. Our results provide insights about principles governing isopeptide ligation reactions catalyzed by SrtA and suggest that although cyclization is guided by distance relationship between Lys (?-amine) and Thr (?-carboxyl) residues, facile branched oligomerization requires the presence of a stable and long-lived acyl-enzyme intermediate. PMID:21566128

Dasgupta, Sayani; Samantaray, Sharmishtha; Sahal, Dinkar; Roy, Rajendra P.

2011-01-01

214

A Brønsted acid catalyzed redox arylation.  

PubMed

A Brønsted acid catalyzed redox arylation of ynamides that employs aryl sulfoxides as the arylating agents is reported. This metal-free transformation proceeds at room temperature and efficiently affords ?-arylated oxazolidinones in a redox-neutral, atom-economic fashion. PMID:24590501

Peng, Bo; Huang, Xueliang; Xie, Lan-Gui; Maulide, Nuno

2014-08-11

215

Stochastic Simulation of Enzyme-Catalyzed Reactions with Disparate Timescales  

E-print Network

Stochastic Simulation of Enzyme-Catalyzed Reactions with Disparate Timescales Debashis Barik-steady-state approximation'' for enzyme-catalyzed reactions provides a useful framework for efficient and accurate stochastic simulations. The method is applied to three examples: a simple enzyme-catalyzed reaction where enzyme

Paul, Mark

216

Helium Catalyzed D-D Fusion in a Levitated Dipole  

E-print Network

Helium Catalyzed D-D Fusion in a Levitated Dipole Jay Kesner, L. Bromberg, MIT D.T. Garnier, A based on the levitated dipole fusion concept that uses a "helium catalyzed D-D" fuel cycle, where rapid ü "Helium catalyzed D-D" fusion cycle ü Summary of Dipole Physics ÿ Linear and non-linear MHD

217

Palladium-catalyzed amination of aryl nonaflates.  

PubMed

The first detailed study of the palladium-catalyzed amination of aryl nonaflates is reported. Use of ligands 2-4 and 6 allows for the catalytic amination of electron-rich and -neutral aryl nonaflates with both primary and secondary amines. With use of Xantphos 5, the catalytic amination of a variety of functionalized aryl nonaflates resulted in excellent yields of anilines; even 2-carboxymethyl aryl nonaflate is effectively coupled with a primary alkylamine. Moderate yields were obtained when coupling halo-aryl nonaflates with a variety of amines, where in most cases the aryl nonaflate reacted in preference to the aryl halide. Overall, aryl nonaflates are an effective alternative to triflates in palladium-catalyzed C-N bond-forming processes due to their increased stability under the reaction conditions. PMID:14656080

Anderson, Kevin W; Mendez-Perez, Maria; Priego, Julian; Buchwald, Stephen L

2003-12-12

218

Enzyme-Catalyzed Processes in Organic Solvents  

Microsoft Academic Search

Three different lipases (porcine pancreatic, yeast, and mold) can vigorously act as catalysts in a number of nearly anhydrous organic solvents. Various transesterification reactions catalyzed by porcine pancreatic lipase in hexane obey Michaelis-Menten kinetics. The dependence of the catalytic activity of the enzyme in organic media on the pH of the aqueous solution from which it was recovered is bell-shaped,

Aleksey Zaks; Alexander M. Klibanov

1985-01-01

219

Peroxidase-catalyzed oxidation of pentachlorophenol.  

PubMed

Pentachlorophenol (PCP) was shown to function as a reducing substrate for horseradish peroxidase (HRP) and to stimulate the HRP-catalyzed reduction of 5-phenyl-4-penten-1-yl hydroperoxide (PPHP) to 5-phenyl-4-penten-1-ol. HRP catalyzed the hydroperoxide-dependent oxidation of PCP, using H2O2, PPHP, or ethyl hydroperoxide as substrates, as evidenced by UV spectroscopic and reverse phase HPLC analysis of reaction mixtures. The major oxidation product was tetrachloro-1,4-benzoquinone which was identified on the basis of electronic absorption spectroscopy, mass spectrometry, and cochromatography with authentic standard. HRP-catalyzed oxidation of PCP yielded relatively stable, ESR-detectable pentachlorophenoxyl radical intermediates whose ESR spectra consisted of a symmetrical single line without hyperfine structure. Substitution of natural abundance isotopically-labeled PCP with 13C-labeled PCP resulted in broadening of the ESR signal line width from 6.1 G to 13.5 G. ESR spin trapping studies, with alpha-(1-oxy-4-pyridyl)-N tert-butylnitrone (4-POBN) as the spin trap demonstrated identical spectra using natural abundance isotopically-labeled PCP versus 13C-labeled PCP, suggesting oxyl addition, rather than carbon-centered radical addition to 4-POBN. The computer simulation of the observed spectra is consistent with two distinct 4-POBN adducts, with relative abundances of approximately 3:1, and hyperfine coupling constants of alpha N = (14.61 G)/alpha H = 1.83 G and alpha N = (14.76 G)/alpha H = 5.21 G, respectively. Mechanisms for the hydroperoxide-dependent, HRP-catalyzed oxidation of PCP are presented that are consistent with these results. PMID:7578920

Samokyszyn, V M; Freeman, J P; Maddipati, K R; Lloyd, R V

1995-01-01

220

Gold(I)-catalyzed enantioselective cycloaddition reactions  

PubMed Central

Summary In recent years there have been extraordinary developments of gold(I)-catalyzed enantioselective processes. This includes progress in the area of cycloaddition reactions, which are of particular interest due to their potential for the rapid construction of optically active cyclic products. In this article we will summarize some of the most remarkable examples, emphasizing reaction mechanisms and key intermediates involved in the processes. PMID:24204438

2013-01-01

221

Rhodium catalyzed direct arylation of ?-diazoimines.  

PubMed

An efficient rhodium catalyzed direct arylation of ?-diazoimines, generated from readily accessible 1,2,3-triazole, has been accomplished for the synthesis of 2,2-diaryl enamides. The reaction involves the chemo- and regioselective insertion of rhodium azavinyl carbene into aromatic C(sp(2))-H bonds. Utility of the developed methodology was demonstrated in the synthesis of indole and tetrahydroisoquinoline frameworks. PMID:24724575

Yadagiri, Dongari; Anbarasan, Pazhamalai

2014-05-01

222

Lipase catalyzed alcoholysis of sunflower oil  

Microsoft Academic Search

Lipase-catalyzed alcoholysis of sunflower oil under anhydrous conditions was examined. Lipases fromPseudomonas fluorescens and 2 immobilized enzymes fromMucor miehei and aCandida sp. gave sufficient conversion with petroleum ether as the solvent, even when methanol and ethanol were used. The overall content\\u000a of tri-, di- and monoglycerides, as well as the corresponding alkyl esters, was measured. BecausePseudomonas lipase led to almost

Martin Mittelbach; Karl Franzens

1990-01-01

223

THE CHALLENGES OF MUON CATALYZED FUSION  

Microsoft Academic Search

This is a survey of new and significant developments which promise to shape the future of muon catalyzed fusion, based on presentations made at the 1988 MuCF workshop. The new ideas about muon production, muon sticking, regeneration and the muomolecular reactions represent steady progress towards understanding of the basic physics of MuCF and reaching towards 1,000 fusions per muon. I

Johann Rafelski

1989-01-01

224

Antiproton catalyzed microfission/fusion propulsion  

NASA Technical Reports Server (NTRS)

Inertial confinement fusion (ICF) utilizing an antiproton catalyzed hybrid fission/fusion target is discussed as a potential energy source for interplanetary propulsion. A proof-of-principle experiment underway at Phillips Laboratory, Kirtland AFB and antiproton trapping experiments at CERN, Geneva, Switzerland, are presented. The ICAN propulsion concept is described and results of performance analyses are reviewed. Future work to further define the ICAN concept is outlined.

Chiang, Pi-Ren; Lewis, Raymond A.; Smith, Gerald A.; Newton, Richard; Dailey, James; Werthman, W. Lance; Chakrabarti, Suman

1994-01-01

225

Palladium-catalyzed oxidative carbonylation reactions.  

PubMed

Palladium-catalyzed coupling reactions have become a powerful tool for advanced organic synthesis. This type of reaction is of significant value for the preparation of pharmaceuticals, agrochemicals, as well as advanced materials. Both, academic as well as industrial laboratories continuously investigate new applications of the different methodologies. Clearly, this area constitutes one of the major topics in homogeneous catalysis and organic synthesis. Among the different palladium-catalyzed coupling reactions, several carbonylations have been developed and widely used in organic syntheses and are even applied in the pharmaceutical industry on ton-scale. Furthermore, methodologies such as the carbonylative Suzuki and Sonogashira reactions allow for the preparation of interesting building blocks, which can be easily refined further on. Although carbonylative coupling reactions of aryl halides have been well established, palladium-catalyzed oxidative carbonylation reactions are also interesting. Compared with the reactions of aryl halides, oxidative carbonylation reactions offer an interesting pathway. The oxidative addition step could be potentially avoided in oxidative reactions, but only few reviews exist in this area. In this Minireview, we summarize the recent development in the oxidative carbonylation reactions. PMID:23307763

Wu, Xiao-Feng; Neumann, Helfried; Beller, Matthias

2013-02-01

226

Molecular cloning and transcriptional activity of a new Petunia calreticulin gene involved in pistil transmitting tract maturation, progamic phase, and double fertilization.  

PubMed

Calreticulin (CRT) is a highly conserved and ubiquitously expressed Ca²?-binding protein in multicellular eukaryotes. As an endoplasmic reticulum-resident protein, CRT plays a key role in many cellular processes including Ca²? storage and release, protein synthesis, and molecular chaperoning in both animals and plants. CRT has long been suggested to play a role in plant sexual reproduction. To begin to address this possibility, we cloned and characterized the full-length cDNA of a new CRT gene (PhCRT) from Petunia. The deduced amino acid sequence of PhCRT shares homology with other known plant CRTs, and phylogenetic analysis indicates that the PhCRT cDNA clone belongs to the CRT1/CRT2 subclass. Northern blot analysis and fluorescent in situ hybridization were used to assess PhCRT gene expression in different parts of the pistil before pollination, during subsequent stages of the progamic phase, and at fertilization. The highest level of PhCRT mRNA was detected in the stigma-style part of the unpollinated pistil 1 day before anthesis and during the early stage of the progamic phase, when pollen is germinated and tubes outgrow on the stigma. In the ovary, PhCRT mRNA was most abundant after pollination and reached maximum at the late stage of the progamic phase, when pollen tubes grow into the ovules and fertilization occurs. PhCRT mRNA transcripts were seen to accumulate predominantly in transmitting tract cells of maturing and receptive stigma, in germinated pollen/growing tubes, and at the micropylar region of the ovule, where the female gametophyte is located. From these results, we suggest that PhCRT gene expression is up-regulated during secretory activity of the pistil transmitting tract cells, pollen germination and outgrowth of the tubes, and then during gamete fusion and early embryogenesis. PMID:24213153

Lenartowski, Robert; Suwi?ska, Anna; Prusi?ska, Justyna; Gumowski, Krzysztof; Lenartowska, Marta

2014-02-01

227

Calreticulin as a hydrophilic chimeric molecular adjuvant enhances IgG responses to the spike protein of severe acute respiratory syndrome coronavirus.  

PubMed

Fragment 450-650 of the spike (S) protein (S450-650) of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) contains epitopes capable of being recognized by convalescent sera of SARS patients. Vaccination of mice with recombinant S450-650 (rS450-650) can induce Abs against SARS-CoV, although the titer is relatively low. In the present study, a fusion protein linking a fragment (residues 39-272) of murine calreticulin (CRT) to S450-650 in a prokaryotic expression system was created. Compared with target antigen alone, the recombinant fusion product (rS450-650-CRT) has much improved hydrophilicity and immunogenicity. The S450-650-specific IgG Abs of BALB/c mice subcutaneously immunized with rS450-650-CRT were in substantially higher titer (approximately fivefold more). Furthermore, the fusion protein, but not rS450-650 alone, was able to elicit S450-650-specific IgG responses in T cell deficient nude mice. Given that rCRT/39-272 can drive the maturation of bone-marrow-derived dendritic cells, directly activate macrophages and B cells, and also elicit helper T cell responses in vivo, we propose that fragment 39-272 of CRT is an effective molecular adjuvant capable of enhancing target Ag-specific humoral responses in both a T cell-dependent and independent manner. Fusion protein rS450-650-CRT is a potential candidate vaccine against SARS-CoV infection. PMID:22530918

Qiu, Xiang; Hong, Chao; Li, Yue; Bao, Wanrong; Gao, Xiao-Ming

2012-08-01

228

Gold-catalyzed synthesis of iodofulvenes.  

PubMed

We report the gold-catalyzed synthesis of highly functionalized iodofulvenes from iododialkynes under mild conditions. The catalytic cycle involves the formation of gold acetylides and vinylgold intermediates. These intermediates can then undergo an unprecedented iodine/gold exchange. This new pathway for catalyst transfer in dual gold catalysis opens up the possibility of highly regioselective transformations directed by the gold in the organogold intermediates. The resulting products are well suited for further metal-mediated coupling reactions, allowing the synthesis of extended ?-systems. PMID:23653259

Nösel, Pascal; Lauterbach, Tobias; Rudolph, Matthias; Rominger, Frank; Hashmi, A Stephen K

2013-06-24

229

The Palladium-Catalyzed Trifluoromethylation of Vinyl Sulfonates  

E-print Network

A method for the palladium-catalyzed trifluoromethylation of cyclohexenyl sulfonates has been developed. Various cyclohexenyl triflates and nonaflates underwent trifluoromethylation under mild reaction conditions using a ...

Cho, Eun Jin

230

Metal-Catalyzed Cross-Coupling Reactions for Indoles  

NASA Astrophysics Data System (ADS)

Metal-catalyzed cross-coupling reactions for indoles are reviewed. Palladium-catalyzed cross-coupling reactions are the most widely explored and applied of all metal-catalyzed cross-coupling reactions. Applications of Kumada coupling, Negishi coupling, Suzuki coupling, Stille coupling, Sonogashira reaction, the Heck reaction, carbonylation, and C-N bond formation reactions in indoles are summarized. In addition, other transition metal-catalyzed cross-coupling reactions using copper, rhodium, iron, and nickel in indole synthesis are also discussed.

Li, Jie Jack; Gribble, Gordon W.

231

In Silico and In Vitro Studies on the Protein-Protein Interactions between Brugia malayi Immunomodulatory Protein Calreticulin and Human C1q  

PubMed Central

Filarial parasites modulate effective immune response of their host by releasing a variety of immunomodulatory molecules, which help in the long persistence of the parasite within the host. The present study was aimed to characterize an immunomodulatory protein of Brugia malayi and its interaction with the host immune component at the structural and functional level. Our findings showed that Brugia malayi Calreticulin (BmCRT) is responsible for the prevention of classical complement pathway activation via its interaction with the first component C1q of the human host. This was confirmed by inhibition of C1q dependent lysis of immunoglobulin-sensitized Red Blood Cells (S-RBCs). This is possibly the first report which predicts CRT-C1q interaction on the structural content of proteins to explain how BmCRT inhibits this pathway. The molecular docking of BmCRT-C1q complex indicated that C1qB chain (IgG/M and CRP binding sites on C1q) played a major role in the interaction with conserved and non-conserved regions of N and P domain of BmCRT. Out of 37 amino acids of BmCRT involved in the interaction, nine amino acids (Pro126, Glu132, His147, Arg151, His153, Met154, Lys156, Ala196 and Lys212) are absent in human CRT. Both ELISA and in silico analysis showed the significant role of Ca+2 in BmCRT-HuC1q complex formation and deactivation of C1r2–C1s2. Molecular dynamics studies of BmCRT-HuC1q complex showed a deviation from ?0.4 nm to ?1.0 nm. CD analyses indicated that BmCRT is composed of 49.6% ? helix, 9.6% ? sheet and 43.6% random coil. These findings provided valuable information on the architecture and chemistry of BmCRT-C1q interaction and supported the hypothesis that BmCRT binds with huC1q at their targets (IgG/M, CRP) binding sites. This interaction enables the parasite to interfere with the initial stage of host complement activation, which might be helpful in parasites establishment. These results might be utilized for help in blocking the C1q/CRT interaction and preventing parasite infection. PMID:25184227

Yadav, Sunita; Gupta, Smita; Selvaraj, Chandrabose; Doharey, Pawan Kumar; Verma, Anita; Singh, Sanjeev Kumar; Saxena, Jitendra Kumar

2014-01-01

232

Calnexin and Calreticulin Binding to Human Thyroperoxidase Is Required for Its First Folding Step(s) But Is Not Sufficient to Promote Efficient Cell Surface Expression  

Microsoft Academic Search

Human thyroperoxidase (hTPO) is a type I transmembrane-bound heme-containing glycoprotein that catalyzes the synthesis of thyroid hormones. In a previous study we stably expressed hTPO in Chinese hamster ovary cells and observed that after the synthesis, only 20% of the hTPO molecules were recognized by a monoclonal antibody (mAb 15) directed against a conformational structure, and that only 2% were

LAURENCE FAYADAT; SANDRINE SIFFROI-FERNANDEZ; JEANNE LANET; JEAN-LOUIS FRANC

2000-01-01

233

Representing Rate Equations for Enzyme-Catalyzed Reactions  

ERIC Educational Resources Information Center

Rate equations for enzyme-catalyzed reactions are derived and presented in a way that makes it easier for the nonspecialist to see how the rate of an enzyme-catalyzed reaction depends upon kinetic constants and concentrations. This is done with distribution equations that show how the rate of the reaction depends upon the relative quantities of…

Ault, Addison

2011-01-01

234

ENVIRONMENTAL TECHNOLOGY VERIFICATION REPORT: ENVIROFUELS DIESEL FUEL CATALYZER FUEL ADDITIVE  

EPA Science Inventory

EPA's Environmental Technology Verification Program has tested EnviroFuels diesel fuel additive, called the Diesel Fuel Catalyzer. EnviroFuels has stated that heavy-duty on and off road diesel engines are the intended market for the catalyzer. Preliminary tests conducted indicate...

235

Highly efficient iridium-catalyzed asymmetric hydrogenation of ?-acylamino nitroolefins.  

PubMed

The first highly efficient Ir-catalyzed enantioselective hydrogenation of ?-acylamino nitroolefins is reported. This reaction provides straightforward access to chiral ?-amino nitroalkanes in high yields and excellent enantioselectivities (up to >99.9% ee) catalyzed by an Ir-(R,R)-f-spiroPhos complex. PMID:25213369

Yan, Qiaozhi; Liu, Man; Kong, Duanyang; Zi, Guofu; Hou, Guohua

2014-11-01

236

Mechanism of combustion of catalyzed double base propellants  

Microsoft Academic Search

Existing combustion models, namely, photo chemical theory, chelate and ..pi..-complex theory, and free radical mechanism and carbon\\/carbonaceous matter formation theory, for catalyzed double base propellants have been evaluated in the light of the experimental findings of the present study. Results obtained suggest that carbon formation and its availability to catalyze the reactions in foam and fizz zones are the probable

H. Singh; K. R. K. Rao

1988-01-01

237

Synthetic applications of gold-catalyzed ring expansions  

PubMed Central

Summary The development of new methodologies catalyzed by late transition metals involving cycloisomerizations of strained rings can open new venues for the synthesis of structurally complex molecules with interesting biological activities. Herein we summarize, from both a synthetic as well as a mechanistic point of view, the most recent developments in gold-catalyzed ring expansions. PMID:21772928

Garayalde, David

2011-01-01

238

Mammalian Tyrosinase Catalyzes Three Reactions in the Biosynthesis of Melanin  

Microsoft Academic Search

The biosynthesis of melanin is initiated by the catalytic oxidation of tyrosine to dopa by tyrosinase in a reaction that requires dopa as a cofactor. Tyrosinase then catalyzes the dehydrogenation of dopa to dopaquinone. The subsequent reactions can proceed spontaneously in vitro. Tyrosinase, purified from murine melanomas and the skins of brown mice, has now been shown to catalyze a

Ann Korner; John Pawelek

1982-01-01

239

Enzyme-catalyzed synthesis of aliphatic-aromatic oligoamides.  

PubMed

Enzymatically catalyzed polycondensation of p-xylylenediamine and diethyl sebacate resulted in oligo(p-xylylene sebacamide) with high melting temperatures (223-230 °C) and the enzymatic polycondensation of dimethyl terephthalate and 1,8-diaminooctane leads to oligo(octamethylene terephthalamide) with two melting temperatures at 186 and 218 °C. No oligoamides, but products 1 and 2, were formed from the enzymatic reaction of dimethyl terephthalate and p-xylylenediamine. All reactions were catalyzed by CAL-B, icutinase, or CLEA cutinase. All reactions catalyzed by CAL-B show higher conversion than reactions catalyzed by icutinase or CLEA cutinase. The highest DPmax of 15 was achieved in a one-step and two-step synthesis of oligo(p-xylylene sebacamide) catalyzed by CLEA cutinase. PMID:23544613

Stavila, E; Alberda van Ekenstein, G O R; Loos, K

2013-05-13

240

RNA-Catalyzed RNA Ligation on an External RNA Template  

NASA Technical Reports Server (NTRS)

Variants of the hc ligase ribozyme, which catalyzes ligation of the 3' end of an RNA substrate to the 5' end of the ribozyme, were utilized to evolve a ribozyme that catalyzes ligation reactions on an external RNA template. The evolved ribozyme catalyzes the joining of an oligonucleotide 3'-hydroxyl to the 5'-triphosphate of an RNA hairpin molecule. The ribozyme can also utilize various substrate sequences, demonstrating a largely sequence-independent mechanism for substrate recognition. The ribozyme also carries out the ligation of two oligonucleotides that are bound at adjacent positions on a complementary template. Finally, it catalyzes addition of mononucleoside '5-triphosphates onto the '3 end of an oligonucleotide primer in a template-dependent manner. The development of ribozymes that catalyze polymerase-type reactions contributes to the notion that an RNA world could have existed during the early history of life on Earth.

McGinness, Kathleen E.; Joyce, Gerald F.

2002-01-01

241

Fabrication of catalyzed ion transport membrane systems  

DOEpatents

Process for fabricating a catalyzed ion transport membrane (ITM). In one embodiment, an uncatalyzed ITM is (a) contacted with a non-reducing gaseous stream while heating to a temperature and for a time period sufficient to provide an ITM possessing anion mobility; (b) contacted with a reducing gaseous stream for a time period sufficient to provide an ITM having anion mobility and essentially constant oxygen stoichiometry; (c) cooled while contacting the ITM with the reducing gaseous stream to provide an ITM having essentially constant oxygen stoichiometry and no anion mobility; and (d) treated by applying catalyst to at least one of (1) a porous mixed conducting multicomponent metallic oxide (MCMO) layer contiguous with a first side of a dense layer of MCMO and (2) a second side of the dense MCMO layer. In another embodiment, these steps are carried out in the alternative order of (a), (d), (b), and (c).

Carolan, Michael Francis; Kibby, Charles Leonard

2013-06-04

242

Theoretical survey of muon catalyzed fusion  

SciTech Connect

The main steps in the muon-catalyzed d-t fusion cycle are given in this report. Most of the stages are very fast, and therefore do not contribute significantly to the cycling time. Thus at liquid H/sub 2/ densities (/phi/ = 1 in the standard convention) the time for stopping the negative muon, its subsequent capture and deexcitation to the ground state is estimated to be /approximately/ 10/sup/minus/11/ sec./sup 1/ The muon spends essentially all of its time in either the (d..mu..) ground state, waiting for transfer to a (t..mu..) ground state to occur, or in the (t..mu..) ground state, writing for molecular formation to occur. Following the formation of this ''mesomolecule'' (actually a muonic molecular ion), deexcitation and fusion are again fast. Then the muon is (usually) liberated to go around again. We will discuss these steps in some detail. 5 refs., 3 figs.

Leon, M.

1988-01-01

243

Enzyme-catalyzed degradation of carbon nanomaterials  

NASA Astrophysics Data System (ADS)

Carbon nanotubes and graphene, the nanoscale sp 2 allotropes of carbon, have garnered widespread attention as a result of their remarkable electrical, mechanical, and optical properties and the promise of new technologies that harness these properties. Consequently, these carbon nanomaterials (CNMs) have been employed for diverse applications such as electronics, sensors, composite materials, energy conversion devices, and nanomedicine. The manufacture and eventual disposal of these products may result in the release of CNMs into the environment and subsequent exposure to humans, animals, and vegetation. Given the possible pro-inflammatory and toxic effects of CNMs, much attention has been focused on the distribution, toxicity, and persistence of CNMs both in living systems and the environment. This dissertation will guide the reader though recent studies aimed at elucidating fundamental insight into the persistence of CNMs such as carbon nanotubes (CNTs) and graphene derivatives (i.e., graphene oxide and reduced graphene oxide). In particular, in-testtube oxidation/degradation of CNMs catalyzed by peroxidase enzymes will be examined, and the current understanding of the mechanisms underlying these processes will be discussed. Finally, an outlook of the current field including in vitro and in vivo biodegradation experiments, which have benefits in terms of human health and environmental safety, and future directions that could have implications for nanomedical applications such as imaging and drug delivery will be presented. Armed with an understanding of how and why CNMs undergo enzyme-catalyzed oxidation/biodegradation, researchers can tailor the structure of CNMs to either promote or inhibit these processes. For example, in nanomedical applications such as drug delivery, the incorporation of carboxylate functional groups could facilitate biodegradation of the nanomaterial after delivery of the cargo. Also, the incorporation of CNMs with defect sites in consumer goods could provide a mechanism that promotes the degradation of these materials once these products reach landfills.

Kotchey, Gregg P.

244

Nickel-catalyzed reductive carboxylation of styrenes using CO2.  

PubMed

A nickel-catalyzed reductive carboxylation of styrenes using CO2 has been developed. The reaction proceeds under mild conditions using diethylzinc as the reductant. Preliminary data suggests the mechanism involves two discrete nickel-mediated catalytic cycles, the first involving a catalyzed hydrozincation of the alkene followed by a second, slower nickel-catalyzed carboxylation of the in situ formed organozinc reagent. Importantly, the catalyst system is very robust and will fixate CO2 in good yield even if exposed to only an equimolar amount introduced into the headspace above the reaction. PMID:18928253

Williams, Catherine M; Johnson, Jeffrey B; Rovis, Tomislav

2008-11-12

245

Toluene Monooxygenase-Catalyzed Epoxidation of Alkenes  

PubMed Central

Several toluene monooxygenase-producing organisms were tested for their ability to oxidize linear alkenes and chloroalkenes three to eight carbons long. Each of the wild-type organisms degraded all of the alkenes that were tested. Epoxides were produced during the oxidation of butene, butadiene, and pentene but not hexene or octadiene. A strain of Escherichia coli expressing the cloned toluene-4-monooxygenase (T4MO) of Pseudomonas mendocina KR1 was able to oxidize butene, butadiene, pentene, and hexene but not octadiene, producing epoxides from all of the substrates that were oxidized. A T4MO-deficient variant of P. mendocina KR1 oxidized alkenes that were five to eight carbons long, but no epoxides were detected, suggesting the presence of multiple alkene-degrading enzymes in this organism. The alkene oxidation rates varied widely (ranging from 0.01 to 0.33 ?mol of substrate/min/mg of cell protein) and were specific for each organism-substrate pair. The enantiomeric purity of the epoxide products also varied widely, ranging from 54 to >90% of a single epoxide enantiomer. In the absence of more preferred substrates, such as toluene or alkenes, the epoxides underwent further toluene monooxygenase-catalyzed transformations, forming products that were not identified. PMID:10788354

McClay, Kevin; Fox, Brian G.; Steffan, Robert J.

2000-01-01

246

Zinc-catalyzed copolymerization of carbon dioxide and propylene oxide  

E-print Network

The zinc-catalyzed copolymerization of carbon dioxide and propylene oxide, which is one of the promising reactions for the utilization of carbon dioxide, has been investigated from various aspects. Above all, considering that supercritical carbon...

Katsurao, Takumi

2012-06-07

247

Maa-Bara : catalyzing change in Nigeria's Niger delta  

E-print Network

Can architecture catalyze economic growth? This thesis serves as a design contribution to the war against poverty by proving that small-scale architectural interventions can propagate large-scale economic growth. It ...

Okiomah, Ogheneruno E. (Ogheneruno Elo)

2011-01-01

248

Copper-catalyzed carboarylation of alkynes via vinyl cations.  

PubMed

Copper-catalyzed arylation of electron rich alkynes reveals stabilized trisubstituted vinyl cation equivalents that react with pendant arene nucleophiles to form all carbon tetrasubstituted alkenes. The new process streamlines the synthesis of important medicinally relevant molecules. PMID:23947578

Walkinshaw, Andrew J; Xu, Wenshu; Suero, Marcos G; Gaunt, Matthew J

2013-08-28

249

ENVIRONMENTAL ASSESSMENT OF THE BASE CATALYZED DECOMPOSITION (BCD) PROCESS  

EPA Science Inventory

This report summarizes laboratory-scale, pilot-scale, and field performance data on BCD (Base Catalyzed Decomposition) and technology, collected to date by various governmental, academic, and private organizations....

250

Bismuth Triflate Catalyzed Friedel-Crafts Acylations of Sydnones.  

E-print Network

??Fisher, Jennifer A., M.S., Department of Chemistry, Wright State University, 2005.Bismuth Triflate Catalyzed Friedel-Crafts Acylations of Sydnones. In the present work, suitably functionalized arylsydnones were… (more)

Fisher, Jennifer Ann

2005-01-01

251

Copper-catalyzed coupling reaction of arylhydrazines and trialkylphosphites.  

PubMed

A novel CuO-catalyzed coupling reaction of arylhydrazines with trialkyl phosphites to afford arylphosphonates is described. The reaction proceeded at 80 °C in air without external reductants, oxidants, and ligands. PMID:24467414

Chen, Sheng-Yan; Zeng, Run-Sheng; Zou, Jian-Ping; Asekun, Olayinka Taiwo

2014-02-01

252

Heterocycles via intramolecular platinum-catalyzed propargylic substitution  

PubMed Central

We report a Pt(II)-catalyzed cyclization of nucleophile-tethered propargylic acetates yielding substituted heterocycles containing multiple heteroatoms including morpholines, dioxanes and sulfamates with high cis-selectivity. PMID:21731116

Liang, Qiren; De Brabander, Jef K.

2011-01-01

253

The Iron-Catalyzed Oxidation of Hydrazine by Nitric Acid  

SciTech Connect

To assess the importance of iron to hydrazine stability, the study of hydrazine oxidation by nitric acid has been extended to investigate the iron-catalyzed oxidation. This report describes those results.

Karraker, D.G.

2001-07-17

254

Palladium-catalyzed phthalazinone synthesis using paraformaldehyde as carbon source.  

PubMed

A palladium-catalyzed one-pot synthesis of phthalazinones from 2-halomethyl benzoates, paraformaldehyde, and aryl hydrazines is described. Various substituted phthalazinones were selectively obtained in good yields using paraformaldehyde as the cheap carbon source (CH). PMID:25265212

Wang, Huamin; Cai, Jinhui; Huang, Huawen; Deng, Guo-Jun

2014-10-17

255

BISMUTH(III) CHLORIDE CATALYZED AZA-DIELS-ALDER REACTION  

Microsoft Academic Search

Bismuth (III) chloride effectively catalyzes aza-Diels-Alder reaction of N-aryl aldimines with nucleophilic olefins for the first time to afford quinoline derivatives in high yields at ambient temperature. IICT Communication No. 4499.

B. V. Subba Reddy; R. Srinivas; J. S. Yadav; T. Ramalingam

2001-01-01

256

The structural basis of RNA-catalyzed RNA polymerization  

E-print Network

The Class I ligase is an artificial ribozyme that catalyzes a reaction chemically identical to a single turnover of RNA-dependent RNA polymerization. Such an activity would have been requisite for the emergence of a ...

Shechner, David M

2010-01-01

257

Nickel-Catalyzed Allylic Substitution of Simple Alkenes  

E-print Network

This report describes a nickel-catalyzed allylic substitution process of simple alkenes whereby an important structural motif, a 1,4-diene, was prepared. The key to success is the use of an appropriate nickel–phosphine ...

Matsubara, Ryosuke

258

Rhodium-catalyzed dehydrogenative borylation of cyclic alkenes  

E-print Network

A rhodium-catalyzed dehydrogenative borylation of cyclic alkenes is described. This reaction provides direct access to cyclic 1-alkenylboronic acid pinacol esters, useful intermediates in organic synthesis. Suzuki–Miyaura ...

Kondoh, Azusa

259

Efficient Pd-Catalyzed Amination Reactions for Heterocycle Functionalization  

E-print Network

The Pd-catalyzed amination of unprotected benzo-fused heterocycles is reported, which allows for greater flexibility and efficiency in the modification of this important class of molecules. The generality of these simple ...

Henderson, Jaclyn L.

260

Enantioselective synthesis of cyclobutanes via sequential Rh-catalyzed bicyclobutanation/Cu-catalyzed homoconjugate addition.  

PubMed

Enantiomerically enriched cyclobutanes are constructed by a three-component process in which t-butyl (E)-2-diazo-5-arylpent-4-enoates are treated with Rh2(S-NTTL)4 to provide enantiomerically enriched bicyclobutanes, which can subsequently engage in homoconjugate addition/enolate trapping sequence to give densely functionalized cyclobutanes with high diastereoselectivity. This three-component, two-catalyst procedure can be carried out in a single flask. Rh2(S-NTTL)4-catalyzed reaction of t-butyl (Z)-2-diazo-5-phenylpent-4-enoate gives the Büchner cyclization product in excellent enantioselectivity. PMID:23758288

Panish, Robert; Chintala, Srinivasa R; Boruta, David T; Fang, Yinzhi; Taylor, Michael T; Fox, Joseph M

2013-06-26

261

Enantioselective Synthesis of Cyclobutanes via Sequential Rh-catalyzed Bicyclobutanation/Cu-catalyzed Homoconjugate Addition  

PubMed Central

Enantiomerically enriched cyclobutanes are constructed by a three-component process in which t-butyl (E)-2-diazo-5-arylpent-4-enoates are treated with Rh2(S-NTTL)4 to provide enantiomerically enriched bicyclobutanes, which can subsequently engage in homoconjugate addition/enolate trapping sequence to give densely functionalized cyclobutanes with high diastereoselectivity. This three-component, two-catalyst procedure can be carried out in a single flask. Rh2(S-NTTL)4–catalyzed reaction of t-butyl (Z)-2-diazo-5-phenylpent-4-enoate gives the Buchner cyclization product in excellent enantioselectivity. PMID:23758288

Panish, Robert; Chintala, Srinivasa R.; Boruta, David T.; Fang, Yinzhi; Taylor, Michael T.; Fox, Joseph M.

2013-01-01

262

Enzyme-catalyzed regioselective transesterification of peracylated sophorolipids  

Microsoft Academic Search

Regioselective transesterifications and hydrolysis of peracylated sophorolipid (SL) derivatives catalyzed by lipases was investigated. This study is the first evaluation of the lipase-catalyzed reactions on the non-lactonic SL derivatives. Four lipases, namely from porcine pancreas (PPL, Type II), Candida rugosa (AYS, TypeVII), Pseudomonas cepacia (PS-30), and Candida antarctica (Novozym 435, carrier fixed lipase fraction B) were used in anhydrous THF

Jason A Carr; Kirpal S Bisht

2003-01-01

263

Mechanisms of transition-metal catalyzed additions to olefins  

E-print Network

are consistent with those observed in asynchronous but concerted Diels-Alder reactions.48 Given the general stereospecificity of rhodium-catalyzed cyclopropanations and this similarity, it seems unlikely that the reaction proceeds in a stepwise manner. A... are consistent with those observed in asynchronous but concerted Diels-Alder reactions.48 Given the general stereospecificity of rhodium-catalyzed cyclopropanations and this similarity, it seems unlikely that the reaction proceeds in a stepwise manner. A...

Nowlan, Daniel Thomas

2005-08-29

264

Surface-catalyzed air oxidation of hydrazines: Environmental chamber studies  

NASA Technical Reports Server (NTRS)

The surface-catalyzed air oxidation reactions of fuel hydrazines were studied in a 6500-liter fluorocarbon-film chamber at 80 to 100 ppm concentrations. First-order rate constants for the reactions catalyzed by aluminum, water-damaged aluminum (Al/Al2O3), stainless steel 304L, galvanized steel and titanium plates with surface areas of 2 to 24 sq m were determined. With 23.8 sq m of Al/Al2O3 the surface-catalyzed air oxidation of hydrazine had a half-life of 2 hours, diimide (N2H2) was observed as an intermediate and traces of ammonia were present in the final product mixture. The Al/Al2O3 catalyzed oxidation of monomethylhydrazine yielded methyldiazine (HN = NCH3) as an intermediate and traces of methanol. Unsymmetrical dimethylhydrazine gave no detectable products. The relative reactivities of hydrazine, MMH and UDMH were 130 : 7.3 : 1.0, respectively. The rate constants for Al/Al2O3-catalyzed oxidation of hydrazine and MMH were proportional to the square of the surface area of the plates. Mechanisms for the surface-catalyzed oxidation of hydrazine and diimide and the formation of ammonia are proposed.

Kilduff, Jan E.; Davis, Dennis D.; Koontz, Steven L.

1988-01-01

265

Mechanism of enzyme-catalyzed phospho group transfer  

SciTech Connect

To understand more fully the mechanism of enzyme-catalyzed phospho group transfer, the stereochemical course at phosphorus of four enzymes has been determined. First, using adenosine (..gamma..-(S)-/sup 16/O, /sup 17/O, /sup 18/O)triphosphate as the substrate, the reaction catalyzed by creatine kinase has been found to proceed with overall inversion of configuration at phosphorus. Second, using adenosine (..beta..-(S)-/sup 16/O, /sup 17/O, /sup 18/O)diphosphate as the substrate, the reaction catalyzed by adenylate kinase has been found also to proceed with overall inversion. Third, the reaction catalyzed by phosphoenolpyruvate carboxylase has been studied using ((S/sub p/)-/sup 16/O, /sup 17/O)thiophospoenolpyruvate as the substrate in H/sub 2/ /sup 18/O. Fourth, using adenosine 5'-O-((..gamma..S/sub p/)-..beta gamma..-/sup 17/O,..gamma..-/sup 17/O,/sup 18/O)(3-thiotriphosphate) as the substrate, the reaction catalyzed by pyruvate carboxylase has been shown to proceed with inversion at phosphorus. This results rules out the chemically and enzymatically precendented composite mechanism that had been proposed for this enzyme and supports a stepwise pathway again involving the intermediacy of carboxyphosphate. The first pair of results supports the growing body of evidence that enzyme-catalyzed phospho group transfer proceeds by an in-line associative mechanism. The second pair of results eliminate mechanistic suggestions of concerted electrocyclic processes in bicarbonate dependent carboxylation reactions.

Hansen, D.E.

1986-01-01

266

Gold-Catalyzed Rearrangements and Beyond  

PubMed Central

Cycloisomerizations of enynes are probably the most representative carbon–carbon bond forming reactions catalyzed by electrophilic metal complexes. These transformations are synthetically useful because chemists can use them to build complex architectures under mild conditions from readily assembled starting materials. However, these transformations can have complex mechanisms. In general, gold(I) activates alkynes in the presence of any other unsaturated functional group by forming an (?2-alkyne)–gold complex. This species reacts readily with nucleophiles, including electron-rich alkenes. In this case, the reaction forms cyclopropyl gold(I) carbene-like intermediates. These can come from different pathways depending on the substitution pattern of the alkyne and the alkene. In the absence of external nucleophiles, 1,n-enynes can form products of skeletal rearrangement in fully intramolecular reactions, which are mechanistically very different from metathesis reactions initiated by the [2 + 2] cycloaddition of a Grubbs-type carbene or other related metal carbenes. In this Account, we discuss how cycloisomerization and addition reactions of substituted enynes, as well as intermolecular reactions between alkynes and alkenes, are best interpreted as proceeding through discrete cationic intermediates in which gold(I) plays a significant role in the stabilization of the positive charge. The most important intermediates are highly delocalized cationic species that some chemists describe as cyclopropyl gold(I) carbenes or gold(I)-stabilized cyclopropylmethyl/cyclobutyl/homoallyl carbocations. However, we prefer the cyclopropyl gold(I) carbene formulation for its simplicity and mnemonic value, highlighting the tendency of these intermediates to undergo cyclopropanation reactions with alkenes. We can add a variety of hetero- and carbonucleophiles to the enynes in the presence of gold(I) in intra- or intermolecular reactions, leading to the corresponding adducts with high stereoselectivity through stereospecific anti-additions. We have also developed stereospecific syn-additions, which probably occur through similar intermediates. The attack of carbonyl groups at the cyclopropyl carbons of the intermediate cyclopropyl gold(I) carbenes initiates a particularly interesting group of reactions. These trigger a cascade transformation that can lead to the formation of two C–C and one C–O bonds. In the fully intramolecular process, this stereospecific transformation has been applied for the synthesis of natural sesquiterpenoids such as (+)-orientalol F and (?)-englerin A. Intra- and intermolecular trapping of cyclopropyl gold(I) carbenes with alkenes leads to the formation of cyclopropanes with significant increase in the molecular complexity, particularly in cases in which this process combines with the migration of propargylic alkoxy and related OR groups. We have recently shown this in the stereoselective total synthesis of the antiviral sesquiterpene (+)-schisanwilsonene by a cyclization/1,5-acetoxy migration/intermolecular cyclopropanation. In this synthesis, the cyclization/1,5-acetoxy migration is faster than the alternative 1,2-acyloxy migration that would result in racemization. PMID:24175907

2013-01-01

267

Microbial-Catalyzed Biotransformation of Multifunctional Triterpenoids Derived from Phytonutrients  

PubMed Central

Microbial-catalyzed biotransformations have considerable potential for the generation of an enormous variety of structurally diversified organic compounds, especially natural products with complex structures like triterpenoids. They offer efficient and economical ways to produce semi-synthetic analogues and novel lead molecules. Microorganisms such as bacteria and fungi could catalyze chemo-, regio- and stereospecific hydroxylations of diverse triterpenoid substrates that are extremely difficult to produce by chemical routes. During recent years, considerable research has been performed on the microbial transformation of bioactive triterpenoids, in order to obtain biologically active molecules with diverse structures features. This article reviews the microbial modifications of tetranortriterpenoids, tetracyclic triterpenoids and pentacyclic triterpenoids. PMID:25003642

Shah, Syed Adnan Ali; Tan, Huey Ling; Sultan, Sadia; Mohd Faridz, Muhammad Afifi Bin; Mohd Shah, Mohamad Azlan Bin; Nurfazilah, Sharifah; Hussain, Munawar

2014-01-01

268

Coalification by clay-catalyzed oligomerization of plant monomers  

SciTech Connect

The main objective of this research program is to devise laboratory methods to mimic the processes by which plants synthesize lignans, lignins and the processes by which these materials are transformed further by geochemical reactions catalyzed by certain clays to coal-like materials. We believe that the radical cation Diels-Alder reaction is one of the principal routes which transforms simple plant materials to coal-like substances and that such reactions may be catalyzed by clays that occur in the environment of the decaying plant materials. Progress is described.

Orchin, M.; Wilson, R.M.

1990-01-01

269

Graphene oxide catalyzed cis-trans isomerization of azobenzene  

NASA Astrophysics Data System (ADS)

We report the fast cis-trans isomerization of an amine-substituted azobenzene catalyzed by graphene oxide (GO), where the amine functionality facilitates the charge transfer from azobenzene to graphene oxide in contrast to non-substituted azobenzene. This catalytic effect was not observed in stilbene analogues, which strongly supports the existence of different isomerization pathways between azobenzene and stilbene. The graphene oxide catalyzed isomerization is expected to be useful as a new photoisomerization based sensing platform complementary to GO-based fluorescence quenching methods.

Shin, Dongha; Kang, Jin Hyoun; Min, Kyung-Ah; Hong, Suklyun; Hee Hong, Byung

2014-09-01

270

New Palladium-Catalyzed Approaches to Heterocycles and Carbocycles  

SciTech Connect

The tert-butylimines of o-(1-alkynyl)benzaldehydes and analogous pyridinecarbaldehydes have been cyclized under very mild reaction conditions in the presence of I{sub 2}, ICl, PhSeCl, PhSCl and p-O{sub 2}NC{sub 6}H{sub 4}SCl to give the corresponding halogen-, selenium- and sulfur-containing disubstituted isoquinolines and naphthyridines, respectively. Monosubstituted isoquinolines and naphthyridines have been synthesized by the metal-catalyzed ring closure of these same iminoalkynes. This methodology accommodates a variety of iminoalkynes and affords the anticipated heterocycles in moderate to excellent yields. The Pd(II)-catalyzed cyclization of 2-(1-alkynyl)arylaldimines in the presence of various alkenes provides an efficient way to synthesize a variety of 4-(1-alkenyl)-3-arylisoquinolines in moderate to excellent yields. The introduction of an ortho-methoxy group on the arylaldimine promotes the Pd-catalyzed cyclization and stabilizes the resulting Pd(II) intermediate, improving the yields of the isoquinoline products. Highly substituted naphthalenes have been synthesized by the palladium-catalyzed annulation of a variety of internal alkynes, in which two new carbon-carbon bonds are formed in a single step under relatively mild reaction conditions. This method has also been used to synthesize carbazoles, although a higher reaction temperature is necessary. The process involves arylpalladation of the alkyne, followed by intramolecular Heck olefination and double bond isomerization. This method accommodates a variety of functional groups and affords the anticipated highly substituted naphthalenes and carbazoles in good to excellent yields. Novel palladium migratiodarylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed. The chemistry works best with electron-rich aromatics, which is in agreement with the idea that these palladium-catalyzed C-H activation reactions parallel electrophilic aromatic substitution. A relatively efficient synthesis of cyclopropanes has been developed using palladium-catalyzed C-H activation chemistry, in which two new carbon-carbon bonds are formed in a single step. This method involves the palladium-catalyzed activation of relatively unreactive C-H bonds, and provides a very efficient way to synthesize cyclopropapyrrolo[1,2-a]indoles, analogues of the mitomycin antibiotics.

Qinhua Huang

2004-12-19

271

Nickel-catalyzed coupling reactions and synthetic studies toward ent-dioxepandehydrothyrsiferol via an epoxide-opening cascade  

E-print Network

Nickel-Catalyzed Coupling Reactions. Nickel-catalyzed allene--aldehyde coupling and alkene--aldehyde coupling represent two methods of preparing allylic alcohols. Most asymmetric transition metal-catalyzed methods of ...

Ng, Sze-Sze

2008-01-01

272

Nickel-Catalyzed Asymmetric Negishi Cross-Couplings of Racemic Secondary Allylic Chlorides with Alkylzincs  

E-print Network

The transition metal-catalyzed enantioselective coupling of allylic electrophiles with carbon nucleophiles has been the focus of intense investigation.5 Salient examples include palladium-catalyzed couplings with enolates, ...

Fu, Gregory C.

273

Regioselectivity in the Palladium-Catalyzed Addition of Carbon Nucleophiles to Carbocyclic Derivatives  

E-print Network

The regioselectivity of Pd-catalyzed malonate additions and arylations to cycloalkenyl esters can be predicted by completing a stereochemical analysis of the Pd--allyl complex. The Pd-catalyzed malonate additions which have

274

A palladium-catalyzed reaction of aryl halides, potassium metabisulfite, and hydrazines.  

PubMed

Aryl N-aminosulfonamides could be easily produced via a palladium-catalyzed coupling of aryl halides, potassium metabisulfite, and hydrazines. Potassium metabisulfite is an excellent equivalent of sulfur dioxide in the reaction of palladium-catalyzed aminosulfonylation. PMID:22945283

Ye, Shengqing; Wu, Jie

2012-10-14

275

The Resolution of Important Pharmaceutical Building Blocks by Palladium-Catalyzed Aerobic Oxidation of Secondary Alcohols  

E-print Network

The Resolution of Important Pharmaceutical Building Blocks by Palladium-Catalyzed Aerobic Oxidation and Mabel Beckman Laboratories of Chemical Synthesis, Division of Chemistry and Chemical Engineering. Abstract: The palladium-catalyzed aerobic oxidative kinetic resolution of key pharmaceutical building

Stoltz, Brian M.

276

Distinct Reactions Catalyzed by Bacterial and Yeast trans-Aconitate Methyltransferases  

E-print Network

-aconitate methyltransferase from the bacterium Escherichia coli catalyzes the monomethyl esterification of trans-aconitate methyltransferase also catalyzes the monomethyl esterification of trans-aconitate, we identify that the methylation

Clarke, Steven

277

Dialkylbiaryl Phosphines in Pd-Catalyzed Amination: A User's Guide  

PubMed Central

Dialkylbiaryl phosphines are a valuable class of ligand for Pd-catalyzed amination reactions and have been applied in a range of contexts. This review attempts to aid the reader in the selection of the best choice of reaction conditions and ligand of this class for the most commonly encountered and practically important substrate combinations. PMID:22432049

Surry, David S.

2012-01-01

278

Bis(amino)cyclopropenylidene (BAC) Catalyzed Aza-Benzoin Reaction.  

PubMed

A bis(amino)cyclopropenylidene (BAC) catalyzed aza-benzoin reaction between aldehydes and phosphinoyl imines has been developed. The reaction is general with a wide range of aromatic aldehydes and aromatic imines. The reaction displays excellent chemoselectivity favoring aza-benzoin products over homobenzoin products. PMID:25272948

Wilde, Myron M D; Gravel, Michel

2014-10-17

279

Ti-Catalyzed Reactions of Hindered Isocyanates with Alcohols  

E-print Network

Ti-Catalyzed Reactions of Hindered Isocyanates with Alcohols Claude Spino,* Marc-Andre´ Joly, Ce with an alcohol or an amine to produce a carbamate or a urea, respectively, with water to produce a primary amine. The reactions between many unhindered isocy- anates and primary alcohols proceed without catalysis

Spino, Claude

280

Nickel-catalyzed decyanation of inert carbon-cyano bonds.  

PubMed

Nickel catalyzed decyanation of aryl and aliphatic cyanides with hydrosilane as the hydride source has been developed. This method is easy to handle, scalable and can be carried out without a glove box. The method has been applied in the cyanide directed functionalization reaction and ?-substitution of benzyl cyanide. PMID:23152958

Patra, Tuhin; Agasti, Soumitra; Akanksha; Maiti, Debabrata

2013-01-01

281

Cu(II) - Catalyzed Hydrazine Reduction of Ferrous Nitrate  

SciTech Connect

This report discusses the results of a study of catalyzed hydrazine reduction of ferrous nitrate. It is apparent that there is a substantial reaction between hydrazine and nitrate ion (or nitric acid) to produce HN3 during both the reduction of Fe(III) and during storage at room temperature.

Karraker, D.G.

2001-10-15

282

Addition of acetic acid to styrene catalyzed by ion exchanger  

Microsoft Academic Search

The possibility of preparation of 1-phenylethyl acetate by direct addition of acetic acid to styrene catalyzed by Ostion KS in the acid cycle has been investigated. The reaction is accompanied by the formation of higher molecular compounds. The effect of temperature, mole ratio of the starting compounds, stabilization of styrene, amount of the catalyst and of its repeated use on

L. ?ervený; A. Marhoul; J. Kozel

1988-01-01

283

Asymmetric Formation of Quaternary Carbon Centers Catalyzed by Novel Chiral  

E-print Network

-cata- lyzed allylations,5 Heck reactions,6 Diels-Alder reac- tions,7 and cyclopropanations.8 Recently, we, 2, Figure 1). High enantioselectivities (>90% ee) have been obtained for Pd-catalyzed allylic do not proceed at room temperature. Because the nucleophilic addition of a phosphine to ethyl 2

Zhang, Xumu

284

Gold-catalyzed propargylic substitutions: Scope and synthetic developments  

PubMed Central

Summary This personal account summarizes our recent developments in gold-catalyzed direct substitutions on propargylic (allylic, benzylic) alcohols, with various nucleophiles (and bi-nucleophiles) based on the ?- and/or ?-acidity of gold(III) complexes. Synthetic developments are also briefly described. PMID:21804883

Debleds, Olivier; Gayon, Eric; Vrancken, Emmanuel

2011-01-01

285

Strictosidine Synthase: Mechanism of a Pictet-Spengler Catalyzing Enzyme  

PubMed Central

The Pictet–Spengler reaction, which yields either a ?-carboline or a tetrahydroquinoline product from an aromatic amine and an aldehyde, is widely utilized in plant alkaloid biosynthesis. Here we deconvolute the role that the biosynthetic enzyme strictosidine synthase plays in catalyzing the stereoselective synthesis of a ?-carboline product. Notably, the rate-controlling step of the enzyme mechanism, as identified by the appearance of a primary kinetic isotope effect (KIE), is the rearomatization of a positively charged intermediate. The KIE of a nonenzymatic Pictet–Spengler reaction indicates that rearomatization is also rate-controlling in solution, suggesting that the enzyme does not significantly change the mechanism of the reaction. Additionally, the pH dependence of the solution and enzymatic reactions provides evidence for a sequence of acid–base catalysis steps that catalyze the Pictet–Spengler reaction. An additional acid-catalyzed step, most likely protonation of a carbinolamine intermediate, is also significantly rate controlling. We propose that this step is efficiently catalyzed by the enzyme. Structural analysis of a bisubstrate inhibitor bound to the enzyme suggests that the active site is exquisitely tuned to correctly orient the iminium intermediate for productive cyclization to form the diastereoselective product. Furthermore, ab initio calculations suggest the structures of possible productive transition states involved in the mechanism. Importantly, these calculations suggest that a spiroindolenine intermediate, often invoked in the Pictet–Spengler mechanism, does not occur. A detailed mechanism for enzymatic catalysis of the ?-carboline product is proposed from these data. PMID:18081287

Maresh, Justin J.; Giddings, Lesley-Ann; Friedrich, Anne; Loris, Elke A.; Panjikar, Santosh; Trout, Bernhardt L.

2010-01-01

286

Cu-Catalyzed Fluorination of Diaryliodonium Salts with KF  

PubMed Central

A mild Cu-catalyzed nucleophilic fluorination of unsymmetrical diaryliodonium salts with KF is described. This protocol preferentially fluorinates less sterically hindered aromatic rings. The reaction exhibits a broad substrate scope and proceeds with high chemoselectivity and functional group tolerance. DFT calculations implicate a CuI/CuIII catalytic cycle. PMID:24063629

Ichiishi, Naoko; Canty, Allan J.; Yates, Brian F.

2014-01-01

287

Palladium(III)-Catalyzed Fluorination of Arylboronic Acid Derivatives  

PubMed Central

A practical, palladium-catalyzed synthesis of aryl fluorides from arylboronic acid derivatives is presented. The reaction is operationally simple and amenable to multi-gram-scale synthesis. Evaluation of the reaction mechanism suggests a single-electron-transfer pathway, involving a Pd(III) intermediate that has been isolated and characterized. PMID:24040932

Tang, Pingping; Murphy, Jennifer M.; Ritter, Tobias

2013-01-01

288

Pd-catalyzed C-H fluorination with nucleophilic fluoride.  

PubMed

The palladium-catalyzed C-H fluorination of 8-methylquinoline derivatives with nucleophilic fluoride is reported. This transformation involves the use of AgF as the fluoride source in combination with a hypervalent iodine oxidant. Both the scope and mechanism of the reaction are discussed. PMID:22844875

McMurtrey, Kate B; Racowski, Joy M; Sanford, Melanie S

2012-08-17

289

Cu-catalyzed fluorination of diaryliodonium salts with KF.  

PubMed

A mild Cu-catalyzed nucleophilic fluorination of unsymmetrical diaryliodonium salts with KF is described. This protocol preferentially fluorinates the smaller aromatic ligand on iodine(III). The reaction exhibits a broad substrate scope and proceeds with high chemoselectivity and functional group tolerance. DFT calculations implicate a Cu(I)/Cu(III) catalytic cycle. PMID:24063629

Ichiishi, Naoko; Canty, Allan J; Yates, Brian F; Sanford, Melanie S

2013-10-01

290

Development of a Lewis Base Catalyzed Selenocyclization Reaction  

ERIC Educational Resources Information Center

The concept of Lewis base activation of selenium Lewis acids has been effectively reduced to practice in the Lewis base catalyzed selenofunctionalization of unactivated olefins. In this reaction, the weakly acidic species, "N"-phenylselenyl succinimide, is cooperatively activated by the addition of a "soft" Lewis base donor (phosphine sulfides,…

Collins, William

2009-01-01

291

Catalyzing Graduate Teaching Assistants' Laboratory Teaching through Design Research  

ERIC Educational Resources Information Center

We report on a study of a laboratory teaching apprenticeship program designed to improve graduate teaching assistant (GTA) performance. To catalyze GTAs as laboratory teachers we constructed learning goals, synthesized previous literature into a design model and a developmental path, and built two instruments to measure 12 strategic pedagogical…

Bond-Robinson, Janet; Rodriques, Romola A. Bernard

2006-01-01

292

Regioselective green anomeric deacetylation catalyzed by lanthanide triflates  

Microsoft Academic Search

Lanthanide triflates, especially Nd(OTf)3, efficiently catalyze the regioselective transesterification of anomeric acetates. This method offers an efficient solution for the otherwise difficult removal of methyl uronates anomeric acetates as well as a green alternative to published protocols since the lanthanide catalysts are non-toxic and may be easily recycled and reused.

Anh Tuan Tran; Sophie Deydier; David Bonnaffé; Christine Le Narvor

2008-01-01

293

Palladium-Catalyzed Hydrogenation DOI: 10.1002/anie.200600263  

E-print Network

­TangPhos- Catalyzed Hydrogenation of N-Tosylimines** Qin Yang, Gao Shang, Wenzhong Gao, Jingen Deng, and Xumu Zhang hydrogenation catalysts for the reduction of N-tosylimines, we have explored this trans- [*] Q. Yang, G. Shang Building, University Park, PA 16802 (USA) Fax: (+1)814-863-8403 E-mail: xumu@chem.psu.edu Q. Yang, Prof. J

Zhang, Xumu

294

Template-directed oligomerization catalyzed by a polynucleotide analog  

NASA Technical Reports Server (NTRS)

A pyrophosphate-linked analog of polycytidylic acid has been synthesized and shown to catalyze the oligomerization of the complementary monomer 2'-deoxyguanosine 3',5'-bisphosphoimidazolide. Analogs of polynucleotides are of interest in studies of the origins of life as possible precursors of the first RNA molecules. These results demonstrate that such molecules are capable of serving as templates for further synthesis.

Visscher, J.; Bakker, C. G.; Van Der Woerd, R.; Schwartz, Alan W.

1989-01-01

295

Gold-Catalyzed Regioselective Dimerization of Aliphatic Terminal Alkynes  

PubMed Central

A gold-catalyzed regioselective homodimerization of aliphatic terminal alkynes is described. Bulky and less Lewis acidic tBuXPhosAuNTf2 is the preferred catalyst, and the additive, anhydrous NaOAc, substantially facilitates the reaction. PMID:22904604

Sun, Sheng; Kroll, Julien; Luo, Yingdong; Zhang, Liming

2012-01-01

296

Copper-catalyzed mild nitration of protected anilines.  

PubMed

A practical copper-catalyzed direct nitration of protected anilines, by using one equivalent of nitric acid as the nitrating agent, has been developed. This procedure features mild reaction conditions, wide structural scope (with regard to both N-protecting group and arene substitution), and high functional-group tolerance. Dinitration with two equivalents of nitric acid is also feasible. PMID:25213167

Hernando, Elier; Castillo, Rafael R; Rodríguez, Nuria; Gómez Arrayás, Ramón; Carretero, Juan C

2014-10-20

297

Palladium-Catalyzed Coupling Reactions of Aryl Chlorides  

Microsoft Academic Search

Collectively, palladium-catalyzed cou- pling reactions represent some of the most powerful and versatile tools avail- able to synthetic organic chemists. Their widespread popularity stems in part from the fact that they are gen- erally tolerant to a large number of functional groups, which allows them to be employed in a wide range of applications. However, for many years a major

Adam F. Littke; Gregory C. Fu

2002-01-01

298

Novobiocin and Coumermycin Inhibit DNA Supercoiling Catalyzed by DNA Gyrase  

Microsoft Academic Search

Novobiocin and coumermycin are known to inhibit the replication of DNA in Escherichia coli. We show that these drugs inhibit the supercoiling of DNA catalyzed by E. coli DNA gyrase, a recently discovered enzyme that introduces negative superhelical turns into covalently circular DNA. The activity of DNA gyrase purified from a coumermycin-resistant mutant strain is resistant to both drugs. The

Martin Gellert; Mary H. O'Dea; Tateo Itoh; Jun-Ichi Tomizawa

1976-01-01

299

Helium Catalyzed D-D Fusion in a Levitated Dipole  

E-print Network

Helium Catalyzed D-D Fusion in a Levitated Dipole Jay Kesner, P.J. Catto, N. Krasheninnikova MIT M, Ann. Phys. 1 (1957) 120. Stable to ideal MHD ballooning when interchange stable No Magnetic Shear Ballooning modes stable when interchange stable Weak resistive mode at high (res but no res 1/3 A 1/3 mode

300

Palladium-catalyzed reductive homocoupling of N'-tosyl arylhydrazines.  

PubMed

A novel procedure for the preparation of biaryl compounds by Pd-catalyzed homocoupling of N'-tosyl arylhydrazine has been described. N'-Tosyl arylhydrazine, as a readily available and stable coupling partner, demonstrated its generality in the homocoupling reactions. The scope of the reaction and possible mechanism have also been investigated. PMID:24158633

Liu, Jin-Biao; Nie, Lin; Yan, Hui; Jiang, Li-Hua; Weng, Jiang; Lu, Gui

2013-12-14

301

Adventures in Gold-Catalyzed Cascade Reactions and Rearrangements  

Microsoft Academic Search

Gold-catalyzed organic transformations have been a hot topic of research in synthetic organic community over the last few years. Amazingly, most of the reactions can be performed under mild conditions using a catalytic amount of gold complexes. One of the widely reported reactions using gold catalysts is heterocyclization that involves an activation of a pi-system followed by a nucleophilic attack

Dinesh Vinod Vidhani

2010-01-01

302

Surface-Catalyzed Chromium(VI) Reduction: The  

E-print Network

Surface-Catalyzed Chromium(VI) Reduction: The TiO2-CrVI-Mandelic Acid System B A O L I N D E N G on chromium solid/solution partitioning and subsurface mi- gration rates. The oxidation of CrIII by molecular

Deng, Baolin

303

Acid-catalyzed dehydrogenation of amine-boranes  

DOEpatents

A method of dehydrogenating an amine-borane using an acid-catalyzed reaction. The method generates hydrogen and produces a solid polymeric [R.sup.1R.sup.2B--NR.sup.3R.sup.4].sub.n product. The method of dehydrogenating amine-boranes may be used to generate H.sub.2 for portable power sources.

Stephens, Frances Helen (Santa Fe, NM); Baker, Ralph Thomas (Los Alamos, NM)

2010-01-12

304

Palladium-Catalyzed Synthesis of N-tert-Prenylindoles  

PubMed Central

Palladium-catalyzed N-tert-prenylation of indoles, tricarbonylchromium-activated indoles, and indolines that occur in high yields (up to 94%) with high tert-prenyl-to-n-prenyl selectivity (up to 12:1) are reported. PMID:23714013

Johnson, Kirsten F.; Van Zeeland, Ryan

2013-01-01

305

Muon catalyzed DT (deuterium-tritium) fusion at low temperature  

Microsoft Academic Search

Several experimental programs are currently under way to study muon catalyzed fusion (MCF). The largest efforts were made at Los Alamos, New Mexico, and at the Swiss Institute for Nuclear Research (SIN). First results indeed confirm the existence of a very rapid DT cycle producing multiple fusions of the type d..mu..t ..-->.. ..cap alpha.. + n + ..mu.. + 17.6

Crowe

1987-01-01

306

Muon reactivation in muon-catalyzed DT fusion  

Microsoft Academic Search

We comprehensively reanalyze and search for the density dependence of the effective muon alpha sticking fraction omegasff observed experimentally in muon catalyzed deuterium-tritium fusion. In our work particular emphasis has been put on the density dependent dense hydrogen stopping power. The main technical details and improvements in this work are: The (alphamu)+ 2s and 2p states are treated independently and

H. E. Rafelski; B. Müller; J. Rafelski; D. Trautmann; R. D. Viollier

1989-01-01

307

Copper-catalyzed intramolecular oxytrifluoromethylthiolation of unactivated alkenes.  

PubMed

A mild, versatile, and convenient method for efficient intramolecular oxytrifluoromethylthiolation of unactivated alkenes catalyzed by Cu(OAc)2 has been developed. The reactions were carried out under aerobic conditions and formed a variety of isoxazolines bearing a -SCF3 substituent. PMID:25274567

Zhu, Liping; Wang, Guoqiang; Guo, Quanping; Xu, Zhaoqing; Zhang, Di; Wang, Rui

2014-10-17

308

Copper-catalyzed regioselective fluorination of allylic halides.  

PubMed

Group activity: A novel copper-catalyzed fluorination of internal allylic bromides and chlorides has been developed by using Et3N?3?HF as the fluorine source. A functional group (FG) within the substrate is required to achieve the allylic fluorination, and a variety of secondary allylic fluoride compounds can be accessed in good yield with excellent regioselectivity. PMID:23775917

Zhang, Zuxiao; Wang, Fei; Mu, Xin; Chen, Pinhong; Liu, Guosheng

2013-07-15

309

Metal-Catalyzed Cleavage of tRNA[superscript Phe  

ERIC Educational Resources Information Center

This laboratory project is one component of a semester-long advanced biochemistry laboratory course that uses several complementary techniques to study tRNA[superscript Phe] conformational changes induced by ligand binding. In this article we describe a set of experiments in which students assay metal-catalyzed hydrolysis of tRNA[superscript Phe]…

Kirk, Sarah R.; Silverstein, Todd P.; McFarlane Holman, Karen L.

2008-01-01

310

Transition-Metal-Catalyzed Carbonylation of Methyl Acetate.  

ERIC Educational Resources Information Center

Presents a study of the rhodium-catalyzed, ioding-promoted carbonylation of methyl acetate. This study provides an interesting contrast between the carbonylation of methyl acetate and the carbonylation of methanol when similar rhodium/iodine catalyst systems are used. (JN)

Polichnowski, S. W.

1986-01-01

311

Pd-Catalyzed C-H Fluorination with Nucleophilic Fluoride  

PubMed Central

The palladium-catalyzed C–H fluorination of 8-methylquinoline derivatives with nucleophilic fluoride is reported. This transformation involves the use of AgF as the fluoride source in combination with a hypervalent iodine oxidant. Both the scope and mechanism of the reaction are discussed. PMID:22844875

McMurtrey, Kate B.; Racowski, Joy M.; Sanford, Melanie S.

2012-01-01

312

Chiral ?-Iodoamines by Urea-Catalyzed Iodocyclization of Trichloroacetimidates  

PubMed Central

Highly enantioselective vicinal iodoamination of olefins is accomplished through the iodocyclization of alkenyl trichloroacetimidates catalyzed by a new chiral Schiff-base urea derivative. The resulting products are converted readily to a variety of polyfunctional amine-containing chiral building blocks. PMID:24416631

Brindle, Cheyenne S.; Yeung, Charles S.

2013-01-01

313

Synthesis of Cyclic Guanidines via Pd-Catalyzed Alkene Carboamination  

PubMed Central

A new approach to the synthesis of substituted 5-membered cyclic guanidines is described. Palladium-catalyzed alkene carboamination reactions between acyclic N-allyl guanidines and aryl or alkenyl halides provide these products in good yield. This method allows access to a number of different cyclic guanidine derivatives in only two steps from readily available allylic amines. PMID:24147839

Zavesky, Blane P.; Babij, Nicholas R.; Fritz, Jonathan A.

2013-01-01

314

Direct Functionalization of Arenes by Primary Alcohol Sulfonate Esters Catalyzed by Gold(III)  

E-print Network

Direct Functionalization of Arenes by Primary Alcohol Sulfonate Esters Catalyzed by Gold catalyzed by gold have been a focus of attention recently.1 Gold(I) and gold(III) show unique activity in mediating reactions involving alkynes. In contrast, gold-catalyzed arene functionalization has been less

He, Chuan

315

Gold-Catalyzed Cross-Coupling DOI: 10.1002/anie.201402924  

E-print Network

Gold-Catalyzed Cross-Coupling DOI: 10.1002/anie.201402924 Gold-Catalyzed Allylation of Aryl Boronic Acids: Accessing Cross- Coupling Reactivity with Gold** Mark D. Levin and F. Dean Toste* Abstract: A sp3 �sp2 C�C cross-coupling reaction catalyzed by gold in the absence of a sacrificial oxidant

Toste, Dean

316

Synthesis of 2-Cyclopentenones by Gold(I)-Catalyzed Rautenstrauch Rearrangement  

E-print Network

Synthesis of 2-Cyclopentenones by Gold(I)-Catalyzed Rautenstrauch Rearrangement Xiaodong Shi, David(II) complexes catalyzed the isomerization of 1-ethynyl-2-propenyl acetates (1) to cyclopentenones (eq 1 at the 2 and 3 positions (eq 1). On the basis of recent examples of gold(I)- catalyzed cyclizations

Toste, Dean

317

Structural basis for Diels-Alder ribozyme-catalyzed carbon-carbon bond formation  

Microsoft Academic Search

The majority of structural efforts addressing RNA's catalytic function have focused on natural ribozymes, which catalyze phosphodiester transfer reactions. By contrast, little is known about how RNA catalyzes other types of chemical reactions. We report here the crystal structures of a ribozyme that catalyzes enantioselective carbon-carbon bond formation by the Diels-Alder reaction in the unbound state and in complex with

Alexander Serganov; Sonja Keiper; Lucy Malinina; Valentina Tereshko; Eugene Skripkin; Claudia Höbartner; Anna Polonskaia; Anh Tuân Phan; Richard Wombacher; Ronald Micura; Zbigniew Dauter; Andres Jäschke; Dinshaw J Patel

2005-01-01

318

Effect of ionic liquids on epoxide hydrolase-catalyzed synthesis of chiral Cinzia Chiappe,*a  

E-print Network

Effect of ionic liquids on epoxide hydrolase-catalyzed synthesis of chiral 1,2-diols Cinzia Chiappe Ionic liquids (ILs) offer new possibilities for epoxide hydrolase (EH) catalyzed resolution of epoxides, and stereochemical studies have shown that the reaction catalyzed by EHs generally proceeds with a high product and

Hammock, Bruce D.

319

Reconstitution and Characterization of Aminopyrrolnitrin Oxygenase, a Rieske N-Oxygenase That Catalyzes Unusual  

E-print Network

-Oxygenase That Catalyzes Unusual Arylamine Oxidation*S Received for publication,May 16, 2005, and in revised form, August of Illinois, Urbana, Illinois 61801 Rieske oxygenases catalyze a wide variety of important oxidation reactionsD) that catalyzes the unusual oxidation of an arylamine to an arylnitro group. PrnD from Pseudomonas fluorescens Pf5

Zhao, Huimin

320

Rh-Catalyzed Enyne Cycloisomerization Ping Cao, Bin Wang, and Xumu Zhang*  

E-print Network

-catalyzed cycloisomerization of 1,6-enynes which leads to the formation of 1, 4-dienes (intramolecular Alder- ene reaction)2 (eq 1). Many transition metals have been applied to catalyze this Alder-ene type reaction.3 Both Pd- and Ru- catalyzed Alder-ene reactions have been developed by Trost.4 The intramolecular

Zhang, Xumu

321

Kinetic Mechanism of DNA Polymerization Catalyzed by Human DNA Polymerase ?  

PubMed Central

Eukaryotes require highly accurate and processive DNA polymerases to ensure faithful and efficient replication of their genomes. DNA polymerase ? (Pol?) has been shown to catalyze leading-strand DNA synthesis during replication in vivo, but little is known about the kinetic mechanism of polymerization catalyzed by this replicative enzyme. To elucidate this mechanism, we have generated a truncated, exonuclease-deficient mutant of the catalytic subunit of human Pol? (Pol? exo-) and carried out pre-steady-state kinetic analysis of this enzyme. Our results show that Pol? exo-, as other DNA polymerases, follows an induced-fit mechanism when catalyzing correct nucleotide incorporation. Pol? exo- binds DNA with a KdDNA of 79 nM and dissociates from the E•DNA binary complex with a rate constant of 0.021 s?1. Although Pol? exo- binds a correct incoming nucleotide weakly with a KddTTP of 31 µM, it catalyzes correct nucleotide incorporation at a fast rate constant of 248 s?1 at 20 °C. Both a large reaction amplitude difference (42%) between pulse-chase and pulse-quench assays and a small elemental effect (0.9) for correct dTTP incorporation suggest that a slow conformational change preceding the chemistry step limits the rate of correct nucleotide incorporation. In addition, our kinetic analysis shows that Pol? exo-exhibits low processivity during polymerization. To catalyze leading-strand synthesis in vivo, Pol? likely interacts with its three smaller subunits and additional replication factors in order to assemble a replication complex and significantly enhance its polymerization processivity. PMID:24020356

Zahurancik, Walter J.; Klein, Seth J.; Suo, Zucai

2013-01-01

322

Tax posttranslational modifications and interaction with calreticulin in MT-2 cells and human peripheral blood mononuclear cells of human T cell lymphotropic virus type-I-associated myelopathy/tropical spastic paraparesis patients.  

PubMed

The human retrovirus human T cell lymphotropic virus type-I (HTLV-1) is the etiologic agent of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Axonal degeneration in HAM/TSP patients occurs without neuron infection, with the secreted viral Tax protein proposed to be involved. We previously found that Tax secreted into the culture medium of MT-2 cells (HTLV-1-infected cell line) produced neurite retraction in neuroblastoma cells differentiated to neuronal type. To assess the relevance of Tax posttranslational modifications on this effect, we addressed the question of whether Tax secreted by MT-2 cells and peripheral blood mononuclear cells (PBMCs) of HTLV-1-infected subjects is modified. The interaction of Tax with calreticulin (CRT) that modulates intracellular Tax localization and secretion has been described. We studied Tax localization and modifications in MT-2 cells and its interaction with CRT. Intracellular Tax in MT-2 cells was assessed by flow cytometry, corresponding mainly to a 71-kDa protein followed by western blot. This protein reported as a chimera with gp21 viral protein-confirmed by mass spectrometry-showed no ubiquitination or SUMOylation. The Tax-CRT interaction was determined by confocal microscopy and coimmunoprecipitation. Extracellular Tax from HAM/TSP PBMCs is ubiquitinated according to western blot, and its interaction with CRT was shown by coimmunoprecipitation. A positive correlation between Tax and CRT secretion was observed in HAM/TSP PBMCs and asymptomatic carriers. For both proteins inhibitors and activators of secretion showed secretion through the endoplasmic reticulum-Golgi complex. Tax, present in PBMC culture medium, produced neurite retraction in differentiated neuroblastoma cells. These results suggest that Tax, whether ubiquitinated or not, is active for neurite retraction. PMID:24321043

Medina, Fernando; Quintremil, Sebastian; Alberti, Carolina; Barriga, Andres; Cartier, Luis; Puente, Javier; Ramírez, Eugenio; Ferreira, Arturo; Tanaka, Yuetsu; Valenzuela, Maria Antonieta

2014-04-01

323

Recombinant murine calreticulin fragment 39-272 expands CD1d(hi)CD5+ IL-10-secreting B cells that modulate experimental autoimmune encephalomyelitis in C57BL/6 mice.  

PubMed

Calreticulin (CRT) is a Ca²? binding molecular chaperone in the endoplasmic reticulum, but can also accumulate in soluble form in serum and/or synovial fluid of patients with rheumatic disorders. We have recently shown that a prokaryotically expressed recombinant CRT fragment 39-272 (rCRT/39-272) exhibited potent stimulatory activities against macrophages and B cells. However, intraperitoneal (i.p.) administration of rCRT/39-272 effectively suppressed delayed-type hypersensitivity in mice, attributable to production of anti-CRT Abs favoring Th2 cell differentiation. In this study, we further demonstrate that i.p. injection of rCRT/39-272 reduced disease severity in mouse model of experimental autoimmune encephalomyelitis (EAE), by inhibiting autoantigen-specific Th1 differentiation in vivo. Interestingly, the EAE-modulating effect of rCRT/39-272 was attributed to activation/expansion of CD1d(hi)CD5? IL-10-secreting B (B10) cells rather than induction of CRT-specific antibodies in mice. In vitro, rCRT/39-272 could activate and expand murine splenic B10 cells through a Toll like receptor 4 (TLR4)-dependent pathway. The rCRT-activated B10 cells were able to not only enhance Th2 cell differentiation in vitro but also reduce EAE scores of recipient animals in passive transfer experiments. These results revealed soluble CRT, likely released by tissue cells under stress conditions, as a potentially important multi-faced player in immunoregulation and immunopathological responses. PMID:23523122

Hong, Chao; Zhang, Tengteng; Gao, Xiao-Ming

2013-10-01

324

Gold-catalyzed C(sp3)-H bond functionalization.  

PubMed

C-H bonds are ubiquitous in organic molecules. Homogenous gold-catalyzed direct functionalization of unsaturated C-H bonds has emerged as a powerful method in our synthetic toolbox. However, Csp(3)-H bonds have larger dissociation energy and lower proton acidity, and thus the efficient and exquisitely selective cleavage of this kind of chemical bonds for the formation of new carbon-carbon and carbon-heteroatom bonds is still a great challenge. In this tutorial review, we will highlight the recent achievements of gold-catalyzed oxidative and redox-neutral Csp(3)-H bond functionalization, which opens new avenues for economical and sustainable construction of fine chemicals. PMID:24853478

Xie, Jin; Pan, Changduo; Abdukader, Ablimit; Zhu, Chengjian

2014-08-01

325

Cytochrome c catalyzes the in vitro synthesis of arachidonoyl glycine  

SciTech Connect

Long chain fatty acyl glycines are an emerging class of biologically active molecules that occur naturally and produce a wide array of physiological effects. Their biosynthetic pathway, however, remains unknown. Here we report that cytochrome c catalyzes the synthesis of N-arachidonoyl glycine (NAGly) from arachidonoyl coenzyme A and glycine in the presence of hydrogen peroxide. The identity of the NAGly product was verified by isotope labeling and mass analysis. Other heme-containing proteins, hemoglobin and myoglobin, were considerably less effective in generating arachidonoyl glycine as compared to cytochrome c. The reaction catalyzed by cytochrome c in vitro points to its potential role in the formation of NAGly and other long chain fatty acyl glycines in vivo.

McCue, Jeffrey M.; Driscoll, William J. [Department of Anatomy Physiology and Genetics, Uniformed Services University of the Health Sciences, F. Edward Herbert School of Medicine, 4301 Jones Bridge Road, Bethesda, MD 20814 (United States); Mueller, Gregory P. [Department of Anatomy Physiology and Genetics, Uniformed Services University of the Health Sciences, F. Edward Herbert School of Medicine, 4301 Jones Bridge Road, Bethesda, MD 20814 (United States)], E-mail: gmueller@usuhs.mil

2008-01-11

326

Diameter control of Ti-catalyzed silicon nanowires  

NASA Astrophysics Data System (ADS)

Titanium silicide nanoparticles on silicon substrates catalyze the decomposition of a silicon-containing gas, resulting in accelerated growth of silicon in one direction to form nanowires. Under some processing conditions, however, the Ti-catalyzed growth results in tapered silicon nanowires. The tapered nanowires are typically several microns long with diameters of tens of nanometers near the base and less than 10 nanometers at the tip. We show that the tapering is caused by uncatalyzed deposition of silicon on the sidewalls of the growing nanowires. We demonstrate that introducing chlorine-containing species in the gas phase greatly inhibits the uncatalyzed silicon deposition rate, thus yielding nanowires with uniform diameter along their length. Controlling the nanowire diameter along its length is essential for novel nanowire-based electronic, optical, and optoelectronic applications.

Sharma, S.; Kamins, T. I.; Williams, R. Stanley

2004-07-01

327

Transition-metal-catalyzed C-S bond coupling reaction.  

PubMed

Sulfur-containing molecules such as thioethers are commonly found in chemical biology, organic synthesis, and materials chemistry. While many reliable methods have been developed for preparing these compounds, harsh reaction conditions are usually required in the traditional methods. The transition metals have been applied in this field, and the palladium-catalyzed coupling of thiols with aryl halides and pseudo halides is one of the most important methods in the synthesis of thioethers. Other metals have also been used for the same purpose. Here, we summarize recent efforts in metal-catalyzed C-S bond cross-coupling reactions, focusing especially on the coupling of thiols with aryl- and vinyl halides based on different metals. PMID:24443103

Lee, Chin-Fa; Liu, Yi-Chen; Badsara, Satpal Singh

2014-03-01

328

Polymerization of phenols catalyzed by peroxidase in nonaqueous media  

SciTech Connect

Polymers produced by horseradish-peroxidase-catalyzed coupling of phenols have been explored as potential substitutes for phenol-formaldehyde resins. To overcome low substrate solubilities and product molecular weights in water, enzymatic polymerizations in aqueous-organic mixtures have been examined. Peroxidase vigorously polymerizes a number of phenols in mixtures of water with water-miscible solvents such as dioxane, acetone, dimethylformamide, and methyl formate with the solvent content up to 95%. As a result, various phenolic polymers with average molecular weights from 400 to 2.6 x 10/sup 4/ D were obtained depending on the reaction medium composition and the nature of the phenol. Peroxidase-catalyzed copolymerization of different phenols in 85% dioxane was demonstrated. Poly(p-phenylphenol) and poly(p-cresol) were enzymatically prepared on a gram scale. They had much higher melting points, and in addition, poly(p-phenylphenol) was found to have a much higher electrical conductivity than phenol-formaldehyde resins.

Dordick, J.S.; Marletta, M.A.; Klibanov, A.M.

1987-01-01

329

Nickel-catalyzed Negishi alkylations of styrenyl aziridines.  

PubMed

A nickel-catalyzed cross-coupling reaction between N-sulfonyl aziridines and organozinc reagents is reported. The catalytic system comprises an inexpensive and air-stable Ni(II) source and dimethyl fumarate as ligand. Regioselective synthesis of ?-substituted amines is possible under mild and functional-group-tolerant conditions. The stereoselectivity of the reaction is consistent with a stereoconvergent mechanism wherein the sulfonamide directs C-C bond formation. PMID:22414150

Huang, Chung-Yang; Doyle, Abigail G

2012-06-13

330

The gravitino-stau scenario after catalyzed big bang nucleosynthesis  

SciTech Connect

We consider the impact of catalyzed big bang nucleosynthesis on theories with a gravitino lightest superparticle and a charged slepton next-to-lightest superparticle. In models where the gravitino to gaugino mass ratio is bounded from below, such as gaugino-mediated supersymmetry breaking, we derive a lower bound on the gaugino mass parameter m{sub 1/2}. As a concrete example, we determine the parameter space of gaugino mediation that is compatible with all cosmological constraints.

Kersten, Joern [The Abdus Salam ICTP, Strada Costiera 11, 34014 Trieste (Italy); Schmidt-Hoberg, Kai, E-mail: jkersten@ictp.it, E-mail: kai.schmidt-hoberg@ph.tum.de, E-mail: kai.schmidt.hoberg@desy.de [Physik-Department T30, Technische Universitaet Muenchen, James-Franck-Strasse, 85748 Garching (Germany)

2008-01-15

331

Copper-Catalyzed Oxidative Heck Reactions between Alkyltrifluoroborates and Vinylarenes  

PubMed Central

We report herein that potassium alkyltrifluoroborates can be utilized in oxidative Heck-type reactions with vinyl arenes. The reaction is catalyzed by a Cu(OTf)2/1,10-phenanthroline with MnO2 as the stoichiometric oxidant. In addition to the alkyl Heck, amination, esterification and dimerization reactions of alkyltrifluoroborates are demonstrated under analogous reaction conditions. Evidence for an alkyl radical intermediate is presented. PMID:23734764

Liwosz, Timothy W.; Chemler, Sherry R.

2013-01-01

332

Catalyzed ring opening of epoxides: Application to bioplasticizers synthesis  

Microsoft Academic Search

The ring opening of mono, di or tri-substituted epoxides by acetic anhydride to corresponding diacetates is catalyzed by weak bases such as hydrotalcite in the carbonated form. This reaction is performed at 423K without solvent and the solid catalyst is reused after simple regeneration for 4 runs with constant conversion. Ring-opening of methyl oleate epoxide leads to the formation of

Gabriella Fogassy; Pan Ke; François Figueras; Philippe Cassagnau; Sophie Rouzeau; Valérie Courault; Georges Gelbard; Catherine Pinel

2011-01-01

333

Nickel-catalyzed Suzuki-Miyaura couplings in green solvents.  

PubMed

The nickel-catalyzed Suzuki-Miyaura coupling of aryl halides and phenol-derived substrates with aryl boronic acids using green solvents, such as 2-Me-THF and tert-amyl alcohol, is reported. This methodology employs the commercially available and air-stable precatalyst, NiCl2(PCy3)2, and gives biaryl products in synthetically useful to excellent yields. Using this protocol, bis(heterocyclic) frameworks can be assembled efficiently. PMID:23879392

Ramgren, Stephen D; Hie, Liana; Ye, Yuxuan; Garg, Neil K

2013-08-01

334

Tubulin adenosine diphosphate ribosylation is catalyzed by cholera toxin.  

PubMed

Cholera toxin catalyzed the transfer of radioactive label from [adenine-2,8-3H2]NAD+ or ((32P]NAD+ to rat C6 glioma cell membrane and cytosolic proteins. Labeled proteins were resolved by polyacrylamide-NaDodSO4 gel or two-dimensional gel electrophoresis and stained with Coomassie blue, and the gels were subjected to fluorography or autoradiography. Autoradiograms of gels revealed labeled Mr 42000 and 46000-48000 membrane proteins that are putative subunits of the regulatory component (G/F) of the C6 cell hormone-sensitive adenylate cyclase. Cholera toxin also catalyzed the labeling of several cytosolic proteins including a Mr 54000 protein that was observed in autoradiograms of two-dimensional gels to migrate as an acidic satellite relative to Coomassie-stained C6 cell tubulin. Tubulin modified by ADP-ribosylation would undergo an acid shift relative to the stained unmodified tubulin in two-dimensional gels. The data led us to postulate that tubulin undergoes cholera toxin catalyzed ADP-ribosylation. Bovine brain tubulin prepared by three cycles of warm/cold polymerization/depolymerization was incubated with [32P]NAD+, GTP, and cholera toxin and then subjected to two-dimensional gel electrophoresis. Autoradiograms of the gels revealed the presence of [32P]ADP-ribosylated proteins that migrated as acidic satellites relative to the Coomassie-stained brain alpha and beta tubulin. Peptide maps of bovine brain tubulin and the associated [32P]ADP-ribosylated proteins showed a correspondence between the autoradiographic images and the stained peptide fragments. The data demonstrate that cholera toxin catalyzes the ADP-ribosylation of tubulin. PMID:7126551

Hawkins, D J; Browning, E T

1982-08-31

335

Biaryl Phosphine Ligands in Palladium-Catalyzed Amination  

PubMed Central

Palladium-catalyzed amination of aryl halides has undergone rapid development in the last 12 years. This has been largely driven by implementation of new classes of ligands. Biaryl phosphines have proven to provide especially active catalysts in this context. This review discusses the applications that these catalysts have found in C-N cross-coupling in heterocycle synthesis, pharmaceuticals, materials science and natural product synthesis. PMID:18663711

Surry, David S.

2012-01-01

336

Silver-catalyzed radical phosphonofluorination of unactivated alkenes.  

PubMed

We report herein a mild and catalytic phosphonofluorination of unactivated alkenes. With catalysis by AgNO3, the condensation of various unactivated alkenes with diethyl phosphite and Selectfluor reagent in CH2Cl2/H2O/HOAc at 40 °C led to the efficient synthesis of ?-fluorinated alkylphosphonates with good stereoselectivity and wide functional group compatibility. A mechanism involving silver-catalyzed oxidative generation of phosphonyl radicals and silver-assisted fluorine atom transfer is proposed. PMID:24025164

Zhang, Chengwei; Li, Zhaodong; Zhu, Lin; Yu, Limei; Wang, Zhentao; Li, Chaozhong

2013-09-25

337

Synthesis of heterocycles through transition-metal-catalyzed isomerization reactions.  

PubMed

Metal-catalyzed isomerization of N- and O-allylic systems is emerging as an effective method to form synthetically useful iminium and oxocarbenium intermediates. In the presence of tethered nucleophiles, several recent examples illuminate this approach as a powerful strategy for the synthesis of structurally complex and diverse heterocycles. In this Concept article, we attempt to cover this area of research through a selection of recent versatile examples. PMID:24924616

Ishoey, Mette; Nielsen, Thomas E

2014-07-14

338

Facile Synthesis of Bis(indolyl)methanes Catalyzed by ?-Chymotrypsin.  

PubMed

A mild and efficient method catalyzed by ?-chymotrypsin was developed for the synthesis of bis(indolyl)methanes through a cascade process between indole and aromatic aldehydes. In the ethanol aqueous solution, a green medium, a wide range of aromatic aldehydes could react with indole to afford the desired products with moderate to good yields (from 68% to 95%) using a little ?-chymotrypsin as catalyst. PMID:25438078

Xie, Zong-Bo; Sun, Da-Zhao; Jiang, Guo-Fang; Le, Zhang-Gao

2014-01-01

339

Cerium-catalyzed oxidative C–C bond forming reactions  

Microsoft Academic Search

With respect to economical and ecological considerations, molecular oxygen is the oxidant of choice for functionalization of organic substrates. On the basis of our cerium-catalyzed ?-hydroxylation of ?-dicarbonyl compounds, we have developed an oxidative process for C–C bond formation in the presence of simple olefins like styrene. Products of these reactions, which are isolated as endoperoxidic 1,2-dioxane derivatives with potential

Jens Christoffers; Thomas Werner; Michael Rössle

2007-01-01

340

Gold(I)-Catalyzed Stereoconvergent, Intermolecular Enantioselective Hydroamination of Allenes  

PubMed Central

A 1:2 mixture of [(S)-2](AuCl)2 [(S)-2 = (S)-3,5-t-Bu-4-MeO-MeOBIPHEP] and AgBF4 catalyzes the stereoconvergent, intermolecular enantioselective hydroamination of chiral, racemic 1,3-disubstituted allenes with N-unsubstituted carbamates to form N-allylic carbamates in good yield, with high regio- and diastereoselectivity, and up to 92% ee. PMID:22492591

Butler, Kristina L.; Tragni, Michele; Widenhoefer, Ross A.

2012-01-01

341

Solid acid (superacid) catalyzed regioselective adamantylation of substituted benzenes  

Microsoft Academic Search

Adamantylation of substituted benzenes with 1-bromo-adamantane was catalyzed by solid acids including acidic ion exchange and ionomer resins, HY zeolite, sulfated zirconia and supported superacids on HY zeolite and SiO2. Adamantylation generally takes place in excellent yield giving predominantly para products without formation of byproducts. The reactions did not require the usual workup of Friedel-Crafts reactions as catalysts were simply

George A. Olah; Béla Török; Tatyana Shamma; Marianna Török; G. K. Surya Prakash

1996-01-01

342

Reductive dechlorination catalyzed by bacterial transition-metal coenzymes  

Microsoft Academic Search

The bacterial transition-metal coenzymes vitamin Bââ (Co), coenzyme Fâââ (ni), and hematin (Fe) catalyzed the reductive dechlorination of polychlorinated ethylenes and benzenes, whereas the electron-transfer proteins four-iron ferredoxin, two-iron ferredoxin, and azurin (Cu) did not. For vitamin Bââ and coenzyme Fâââ, reductive dechlorination rates for different classes of perchlorinated compounds had the following order: carbon tetrachloride > tetrachloroethylene > hexachlorobenzene.

Charles J. Gantzer; Lawrence P. Wackett

1991-01-01

343

Synthesis of Graphite Encapsulated Metal Nanoparticles and Metal Catalyzed Nanotubes  

NASA Technical Reports Server (NTRS)

This work focuses on the growth and inception of graphite encapsulated metal nanoparticles and metal catalyzed nanotubes using combustion chemistry. Deciphering the inception and growth mechanism(s) for these unique nanostructures is essential for purposeful synthesis. Detailed knowledge of these mechanism(s) may yield insights into alternative synthesis pathways or provide data on unfavorable conditions. Production of these materials is highly desirable given many promising technological applications.

vanderWal, R. L.; Dravid, V. P.

1999-01-01

344

A simple strategy for glycosyltransferase-catalyzed aminosugar nucleotide synthesis.  

PubMed

A set of 2-chloro-4-nitrophenyl glucosamino-/xylosaminosides were synthesized and assessed as potential substrates in the context of glycosyltransferase-catalyzed formation of the corresponding UDP/TDP-?-D-glucosamino-/xylosaminosugars and in single-vessel model transglycosylation reactions. This study highlights a robust platform for aminosugar nucleotide synthesis and reveals OleD Loki to be a proficient catalyst for U/TDP-aminosugar synthesis and utilization PMID:24677528

Zhang, Jianjun; Singh, Shanteri; Hughes, Ryan R; Zhou, Maoquan; Sunkara, Manjula; Morris, Andrew J; Thorson, Jon S

2014-03-21

345

Muon-catalyzed DT fusion at low temperature  

Microsoft Academic Search

Muon-catalyzed deuterium-tritium fusion was investigated within a wide range of mixtures in liquid and gas (23-35 K) by detection of fusion neutrons. Our improved analysis includes hyperfine effects and allows a clear separation of intrinsic dt sticking omegas from kinetic effects. Strongly density-dependent cycle rates with values up to 1.45×108 s-1, yields of 113 fusions per muon, and omegas=(0.45+\\/-0.05)% are

W. H. Breunlich; M. Cargnelli; P. Kammel; J. Marton; N. Naegele; P. Pawlek; A. Scrinzi; J. Werner; J. Zmeskal; J. Bistirlich; K. M. Crowe; M. Justice; J. Kurck; C. Petitjean; R. H. Sherman; H. Bossy; H. Daniel; F. J. Hartmann; W. Neumann; G. Schmidt

1987-01-01

346

Experimental investigation of muon-catalyzed d-t fusion  

Microsoft Academic Search

Measurements of the absolute neutron yield and the time dependence of the appearance of neutrons resulting from muon-catalyzed fusion have been carried out in high-density deuterium-tritium mixtures. The temperature dependence of the resonant dt..mu..-molecular formation process has been determined in the range 100 to 540 K. Mesomolecular formation is found to be resonant for DT as well as D target

S. E. Jones; A. N. Anderson; A. J. Caffrey; J. B. Walter; K. D. Watts; J. N. Bradbury; P. A. M. Gram; M. Leon; H. R. Maltrud; M. A. Paciotti

1983-01-01

347

Experimental Investigation of Muon-Catalyzed d-t Fusion  

Microsoft Academic Search

Measurements of the absolute neutron yield and the time dependence of the appearance of neutrons resulting from muon-catalyzed fusion have been carried out in high-density deuterium-tritium mixtures. The temperature dependence of the resonant dtmu-molecular formation process has been determined in the range 100 to 540 K. Mesomolecular formation is found to be resonant for DT as well as D2 target

S. E. Jones; A. N. Anderson; A. J. Caffrey; J. B. Walter; K. D. Watts; J. N. Bradbury; P. A. M. Gram; M. Leon; H. R. Maltrud; M. A. Paciotti

1983-01-01

348

Lipase-catalyzed kinetic resolution of aryltrimethylsilyl chiral alcohols.  

PubMed

Lipase-catalyzed kinetic resolution of aryltrimethylsilyl chiral alcohols through a transesterification reaction was studied. The optimal conditions found for the kinetic resolution of m- and p-aryltrimethylsilyl chiral alcohols, led to excellent results, high conversions (c = 50%), high enantiomeric ratios (E > 200) and enantiomeric excesses for the remaining (S)-alcohol and (R)-acetylated product (>99%). However, kinetic resolution of o-aryltrimethylsilyl chiral alcohols did not occur under the same conditions applied to the other isomers. PMID:22113578

Palmeira, Dayvson J; Abreu, Juliana C; Andrade, Leandro H

2011-01-01

349

Uranium(VI)-catalyzed photooxidation of hydrocarbons with molecular oxygen  

SciTech Connect

Uranium(VI) catalyzes the photooxidation of alkanes, alkenes, alcohols, and aldehydes by molecular oxygen in aqueous solution. Despite the mechanistic complexities, each of there actions investigated yielded a single organic product. On the basis of the quenching kinetics, the deuterium isotope effects, the nature of the products, and linear free energy relationships, all the reactions appear to take place by hydrogen atom abstraction from C-H bonds, followed by uranium-mediated product formation.

Wei-Dong Wang; Bakac, A.; Espenson, J.H. [Iowa State Univ., IA (United States)

1995-11-22

350

Involvement of free radicals in peroxidatic reactions catalyzed by chloroperoxidase  

Microsoft Academic Search

The mechanism of chloroperoxidase (CPO)-catalyzed peroxidatic reactions of several substituted hydroquinones was studied at various hydrogen peroxide concentrations. The pathway was studied using cytochrome c as the radical trapping agent. As the hydroquinones became more hindered there was a difference in the amount of radicals trapped. For hydroquinone, 59.3% radical pathway, and methylhydroquinone, 81.4% radical, the difference in radicals trapped

David P. Provencal

1992-01-01

351

Acetalization of Carbonyl Compounds Catalyzed by I2-Doped Polyaniline  

Microsoft Academic Search

Polyaniline-I2 is prepared by doping of polyaniline base with iodine. Polyaniline base and polyaniline-I2 are characterized by infrared spectra, X-ray diffraction spectra, and thermogravimetric analysis. Polyaniline-I2 is used as a catalyst for the first time in acetalization of carbonyl compounds. The catalyzing acetalization of cyclohexanone and propane-1,2-diol is conducted in excellent yields with simple and more environmental benign procedure. This

Genxiang Luo; Miao He; Zhaojin Zhong

2008-01-01

352

Acid-Catalyzed Preparation of Biodiesel from Waste Vegetable Oil: An Experiment for the Undergraduate Organic Chemistry Laboratory  

ERIC Educational Resources Information Center

This undergraduate organic laboratory exercise involves the sulfuric acid-catalyzed conversion of waste vegetable oil into biodiesel. The acid-catalyzed method, although inherently slower than the base-catalyzed methods, does not suffer from the loss of product or the creation of emulsion producing soap that plagues the base-catalyzed methods when…

Bladt, Don; Murray, Steve; Gitch, Brittany; Trout, Haylee; Liberko, Charles

2011-01-01

353

Stau-catalyzed big-bang nucleosynthesis reactions  

SciTech Connect

We study the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a hypothetical long-lived negatively charged, massive leptonic particle (called X{sup -}) such as the supersymmetric (SUSY) particle stau, the scalar partner of the tau lepton. It is known that if the X{sup -} particle has a lifetime of tau{sub X} > or approx. 10{sup 3} s, it can capture a light element previously synthesized in standard BBN and form a Coulombic bound state and induces various types of reactions in which X{sup -} acts as a catalyst. Some of these X{sup -} catalyzed reactions have significantly large cross sections so that the inclusion of the reactions into the BBN network calculation can markedly change the abundances of some elements. We use a high-accuracy three-body calculation method developed by the authors and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

Kamimura, Masayasu [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); Kino, Yasushi [Department of Physics, Tohoku University, Sendai 980-8578 (Japan); Hiyama, Emiko [RIKEN Nishina Center, Wako 351-0198 (Japan)

2010-06-01

354

Protection of Wood from Microorganisms by Laccase-Catalyzed Iodination  

PubMed Central

In the present work, Norway spruce wood (Picea abies L.) was reacted with a commercial Trametes versicolor laccase in the presence of potassium iodide salt or the phenolic compounds thymol and isoeugenol to impart an antimicrobial property to the wood surface. In order to assess the efficacy of the wood treatment, a leaching of the iodinated and polymerized wood and two biotests including bacteria, a yeast, blue stain fungi, and wood decay fungi were performed. After laccase-catalyzed oxidation of the phenols, the antimicrobial effect was significantly reduced. In contrast, the enzymatic oxidation of iodide (I?) to iodine (I2) in the presence of wood led to an enhanced resistance of the wood surface against all microorganisms, even after exposure to leaching. The efficiency of the enzymatic wood iodination was comparable to that of a chemical wood preservative, VP 7/260a. The modification of the lignocellulose by the laccase-catalyzed iodination was assessed by the Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) technique. The intensities of the selected lignin-associated bands and carbohydrate reference bands were analyzed, and the results indicated a structural change in the lignin matrix. The results suggest that the laccase-catalyzed iodination of the wood surface presents an efficient and ecofriendly method for wood protection. PMID:22865075

Engel, J.; Thony-Meyer, L.; Schwarze, F. W. M. R.; Ihssen, J.

2012-01-01

355

Protection of wood from microorganisms by laccase-catalyzed iodination.  

PubMed

In the present work, Norway spruce wood (Picea abies L.) was reacted with a commercial Trametes versicolor laccase in the presence of potassium iodide salt or the phenolic compounds thymol and isoeugenol to impart an antimicrobial property to the wood surface. In order to assess the efficacy of the wood treatment, a leaching of the iodinated and polymerized wood and two biotests including bacteria, a yeast, blue stain fungi, and wood decay fungi were performed. After laccase-catalyzed oxidation of the phenols, the antimicrobial effect was significantly reduced. In contrast, the enzymatic oxidation of iodide (I(-)) to iodine (I(2)) in the presence of wood led to an enhanced resistance of the wood surface against all microorganisms, even after exposure to leaching. The efficiency of the enzymatic wood iodination was comparable to that of a chemical wood preservative, VP 7/260a. The modification of the lignocellulose by the laccase-catalyzed iodination was assessed by the Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) technique. The intensities of the selected lignin-associated bands and carbohydrate reference bands were analyzed, and the results indicated a structural change in the lignin matrix. The results suggest that the laccase-catalyzed iodination of the wood surface presents an efficient and ecofriendly method for wood protection. PMID:22865075

Schubert, M; Engel, J; Thöny-Meyer, L; Schwarze, F W M R; Ihssen, J

2012-10-01

356

Mechanism of the reaction catalyzed by mandelate racemase. 3. Asymmetry in reactions catalyzed by the H297N mutant  

SciTech Connect

Two preceding papers suggest that the active site of mandelate racemase (MR) contains two distinct general acid/base catalysts: Lys 166, which abstracts the {alpha}-proton from (s)-mandelate, and His 297, which abstracts the {alpha}-proton from (R)-mandelate. In this paper the authors report on the properties of the mutant of MR in which His 297 has been converted to asparagine by site-directed mutagenesis (H297N). The structure of H297N, solved by molecular replacement at 2.2-{angstrom} resolution, reveals that no conformational alterations accompany the substitution. As expected, h297N has no detectable MR activity. However, H297N catalyzes the stereospecific elimination of bromide ion from racemic {rho}-(bromomethyl) mandelate to give {rho}-(methyl)-benzoylformate in 45% yield at a rate equal to that measured for wild-type enzyme. The pD dependence of the rate of the exchange reaction catalyzed by H297N reveals a pK{sub a} of 6.4 in D{sub 2}O which is assigned to Lys 166. These observations provide persuasive evidence that the reaction catalyzed by MR does, in fact, proceed via a two-base mechanism in which Lys 166 abstracts the {alpha}-proton from (S)-mandelate and His 297 abstracts the {alpha}-proton from (R)-mandelate. These studies demonstrate the power of site-directed mutagenesis in providing otherwise inaccessible detail about the mechanism of an enzyme-catalyzed reaction.

Landro, J.A.; Kallarakal, A.T.; Ransom, S.C.; Gerlt, J.A.; Kozarich, J.W. (Univ. of Maryland, College Park (United States)); Neidhart, D.J. (Abbott Labs., Abbott Park, IL (United States)); Kenyon, G.L. (Univ. of California, San Francisco (United States))

1991-09-24

357

Gold-catalyzed cyclization reactions of allenol and alkynol derivatives.  

PubMed

Although gold is chemically inert as a bulk metal, the landmark discovery that gold nanoparticles can be effective catalysts has opened up new and exciting research opportunities in the field. In recent years, there has been growth in the number of reactions catalyzed by gold complexes [gold(I) and gold(III)], usually as homogeneous catalysts, because they are soft Lewis acids. In addition, alkynes and allenes have interesting reactivities and selectivities, notably their ability to produce complex structures in very few steps. In this Account, we describe our work in gold catalysis with a focus on the formation of C-C and C-O bonds using allenes and alkynes as starting materials. Of these, oxa- and carbo-cyclizations are perhaps the best known and most frequently studied. We have divided those contributions into sections arranged according to the nature of the starting material (allene versus alkyne). Gold-catalyzed carbocyclizations in allenyl C2-linked indoles, allenyl-?-lactams, and allenyl sugars follow different mechanistic pathways. The cyclization of indole-tethered allenols results in the efficient synthesis of carbazole derivatives, for example. However, the compound produced from gold-catalyzed 9-endo carbocyclization of (aryloxy)allenyl-tethered 2-azetidinones is in noticeable contrast to the 5-exo hydroalkylation product that results from allenyl sugars. We have illustrated the unusual preference for the 4-exo-dig cyclization in allene chemistry, as well as the rare ?-hydride elimination reaction, in gold catalysis from readily available ?-allenols. We have also observed in ?-allenols that a (methoxymethyl)oxy protecting group not only masks a hydroxyl functionality but also exerts directing effects as a controlling unit in a gold-catalyzed regioselectivity reversal. Our recent work has also led to a combined experimental and computational study on regioselective gold-catalyzed synthetic routes to 1,3-oxazinan-2-ones (kinetically controlled products) and 1,3-oxazin-2-one derivatives (thermodynamically favored) from easily accessible allenic carbamates. In addition, we discuss the direct gold-catalyzed cycloketalization of alkynyldioxolanes, as well as aminoketalization of alkynyloxazolidines. We performed labeling studies and density functional calculations to gain insight into the mechanisms of the bis-heterocyclization reactions. We also describe the controlled gold-catalyzed reactions of primary and secondary propargylic hydroperoxides with a variety of nucleophiles including alcohols and phenols, allowing the direct synthesis of ?-functionalized ketones. Through computations and (18)O-labeling experiments, we discovered various aspects of the controlled reactivity of propargylic hydroperoxides with external nucleophiles under gold catalysis. The mechanism resembles a Meyer-Schuster rearrangement, but notably, the presence and geometry characteristics of the OOH functional group allow a new pathway to happen, which cannot apply to propargylic alcohols. PMID:24428670

Alcaide, Benito; Almendros, Pedro

2014-03-18

358

A SABATH Methyltransferase from the moss Physcomitrella patens catalyzes  

SciTech Connect

Known SABATH methyltransferases, all of which were identified from seed plants, catalyze methylation of either the carboxyl group of a variety of low molecular weight metabolites or the nitrogen moiety of precursors of caffeine. In this study, the SABATH family from the bryophyte Physcomitrella patens was identified and characterized. Four SABATH-like sequences (PpSABATH1, PpSABATH2, PpSABATH3, and PpSABATH4) were identified from the P. patens genome. Only PpSABATH1 and PpSABATH2 showed expression in the leafy gametophyte of P. patens. Full-length cDNAs of PpSABATH1 and PpSABATH2 were cloned and expressed in soluble form in Escherichia coli. Recombinant PpSABATH1 and PpSABATH2 were tested for methyltransferase activity with a total of 75 compounds. While showing no activity with carboxylic acids or nitrogen-containing compounds, PpSABATH1 displayed methyltransferase activity with a number of thiols. PpSABATH2 did not show activity with any of the compounds tested. Among the thiols analyzed, PpSABATH1 showed the highest level of activity with thiobenzoic acid with an apparent Km value of 95.5 lM, which is comparable to those of known SABATHs. Using thiobenzoic acid as substrate, GC MS analysis indicated that the methylation catalyzed by PpSABATH1 is on the sulfur atom. The mechanism for S-methylation of thiols catalyzed by PpSABATH1 was partially revealed by homology-based structural modeling. The expression of PpSABATH1 was induced by the treatment of thiobenzoic acid. Further transgenic studies showed that tobacco plants overexpressing PpSABATH1 exhibited enhanced tolerance to thiobenzoic acid, suggesting that PpSABATH1 have a role in the detoxification of xenobiotic thiols.

Zhao, Nan [ORNL; Ferrer, Jean-Luc [Universite Joseph Fourier, France; Moon, Hong S [Department of Plant Sciences, University of Tennessee; Kapteyn, Jeremy [Institute of Biological Chemistry, Washington State University; Zhuang, Xiaofeng [Department of Plant Sciences, University of Tennessee; Hasebe, Mitsuyasu [Laboratory of Evolutionary Biology, National Institute for Biology, 38 Nishigounaka; Stewart, Neal C. [Department of Plant Sciences, University of Tennessee; Gang, David R. [Institute of Biological Chemistry, Washington State University; Chen, Feng [University of Tennessee, Knoxville (UTK)

2012-01-01

359

Rh(I)-Catalyzed Direct Arylation of Azines  

PubMed Central

The Rh(I)-catalyzed direct arylation of azines has been developed. Quinolines and 2-substituted pyridines couple with aryl bromides to efficiently afford ortho-arylated azine products using the commercially available and air stable catalyst [RhCl(CO)2]2. Electron-deficient and rich aromatic bromides couple in good yields, and hydroxyl, chloro, fluoro, trifluoromethyl, ether and ketone functionality are compatible with the reaction conditions. Aroyl chlorides also serve as effective azine coupling partners to give ortho-arylation products via a decarbonylation pathway. PMID:21033740

Berman, Ashley M.; Bergman, Robert G.; Ellman, Jonathan A.

2011-01-01

360

Rh(I)-catalyzed direct arylation of azines.  

PubMed

The Rh(I)-catalyzed direct arylation of azines has been developed. Quinolines and 2-substituted pyridines couple with aryl bromides to efficiently afford ortho-arylated azine products using the commercially available and air-stable catalyst [RhCl(CO)2]2. Electron-deficient and electron-rich aromatic bromides couple in good yields, and hydroxyl, chloro, fluoro, trifluoromethyl, ether, and ketone functionalities are compatible with the reaction conditions. Aroyl chlorides also serve as effective azine coupling partners to give ortho-arylation products via a decarbonylation pathway. PMID:21033740

Berman, Ashley M; Bergman, Robert G; Ellman, Jonathan A

2010-11-19

361

Palladium-Catalyzed Borylation of Primary Alkyl Bromides  

PubMed Central

A mild Pd-catalyzed process for the borylation of alkyl bromides has been developed using bis(pinacolato)diboron as a boron source. This process accommodates the use of a wide range of functional groups on the alkyl bromide substrate. Primary bromides react with complete selectivity in the presence of a secondary bromide. The generality of this approach is demonstrated by its extension to the use of alkyl iodides and alkyl tosylates, as well as borylation reactions employing bis(neopentyl glycolato)diboron as the boron source. PMID:22774861

Joshi-Pangu, Amruta; Ma, Xinghua; Diane, Mohamed; Iqbal, Sidra; Kribs, Robert J.; Huang, Richard; Wang, Chao-Yuan

2012-01-01

362

Stau-catalyzed d-t Nuclear Fusion  

E-print Network

The gravitino of mass 10-100 GeV is a well motivated scenario in supergravity. If the stau is the next lightest supersymmetry particle, its life-time becomes order of $10^{6-8}$ sec. If it is the case the stau makes a big impact on the nuclear fusion, since it is a charged particle. In this paper we perform a detailed calculation of a stau-catalyzed d-t fusion. We find that if certain technical conditions are satisfied, it is not hopeless to use the nuclear fusion as a source of energy.

Koichi Hamaguchi; Tetsuo Hatsuda; Masayasu Kamimura; Tsutomu T. Yanagida

2012-02-13

363

Enantioselective aldol reactions catalyzed by chiral phosphine oxides.  

PubMed

The development of enantioselective aldol reactions catalyzed by chiral phosphine oxides is described. The aldol reactions presented herein do not require the prior preparation of the masked enol ethers from carbonyl compounds as aldol donors. The reactions proceed through a trichlorosilyl enol ether intermediate, formed in situ from carbonyl compounds, which then acts as the aldol donor. Phosphine oxides activate the trichlorosilyl enol ethers to afford the aldol adducts with high stereoselectivities. This procedure was used to realize a directed cross-aldol reaction between ketones and two types of double aldol reactions (a reaction at one/two ? position(s) of a carbonyl group) with high diastereo- and enantioselectivities. PMID:23828817

Kotani, Shunsuke; Sugiura, Masaharu; Nakajima, Makoto

2013-08-01

364

Catalyzed growth of doped TGS single crystals for infrared applications  

NASA Astrophysics Data System (ADS)

Single crystals of triglycine sulphate (TGS) doped with Pr3+ Sm3+, Pd2+, Co2+, Pt4+ and PO43- with L-alanin were grown from aqueous solutions by means of the slow cooling method. Surface morphology, domain structure and P-E hysteresis loops have been investigated. The model of catalyzed growth of {001}and{101}crystal pyramids on the basis of metal-glycine complexes has been suggested. We have found on the basis of experimental results that TGS single crystals doped with Pt4+ and L-alanin are excellent materials for construction of infrared detectors.

Novotny, Jan; Zelinka, J.; Podvalova, Z.

2002-03-01

365

Coalification by clay-catalyzed oligomerization of plant monomers  

SciTech Connect

The chemical structure'' of coal, if indeed there is one, remains an enigma. Over the years numerous chemists have integrated a host of experimental observations to generate various average'' structures which differ greatly. Our approach is to regard the structural question of coal as a problem in natural product chemistry. Our model is that of a macromolecular polymer initially synthesized from monomeric naturally-occuring hydroxy and methoxy substituted propenylbenzenes (C{sub 6}-C{sub 3} units), properly aligned to undergo oligomerization reactions via conventional organic reaction mechanisms, specifically Diels-Alder radical cation condensations, phenolic coupling, and proton-catalyzed isomerization and cyclization.

Orchin, M.; Wilson, R.M.

1991-01-01

366

Iron-catalyzed aromatic amination for nonsymmetrical triarylamine synthesis.  

PubMed

Novel iron-catalyzed amination reactions of various aryl bromides have been developed for the synthesis of diaryl- and triarylamines. The key to the success of this protocol is the use of in situ generated magnesium amides in the presence of a lithium halide, which dramatically increases the product yield. The present method is simple and free of precious and expensive metals and ligands, thus providing a facile route to triarylamines, a recurrent core unit in organic electronic materials as well as pharmaceuticals. PMID:23181635

Hatakeyama, Takuji; Imayoshi, Ryuji; Yoshimoto, Yuya; Ghorai, Sujit K; Jin, Masayoshi; Takaya, Hikaru; Norisuye, Kazuhiro; Sohrin, Yoshiki; Nakamura, Masaharu

2012-12-19

367

Native transfer RNA catalyzes Diels-Alder reaction.  

PubMed

In this paper we show that transfer ribonucleic acids (tRNAs) catalyze the Diels-Alder cycloaddition reaction. A new DNA oxidative damage product, 6-furfuryladenine (kinetin) or its riboside (diene), was transformed with dimethyl acetylenedicarboxylate or maleic anhydride (dienophile). The reaction proceeds in the presence of tRNA at high pressure but not at ambient condition. If so tRNA in prebiotic conditions (RNA world) had at least two functions: catalytic and a carrier of genetic information. It means that tRNA at high pressure shows catalytic properties and is a true Diels-Alderase. PMID:12054754

Mielcarek, Michal; Barciszewska, Miroslawa Z; Sa?anski, Piotr; Stobiecki, Maciej; Jurczak, Janusz; Barciszewski, Jan

2002-05-31

368

Exploring Transition Metal Catalyzed Reactions via AB Initio Reaction Pathways  

NASA Astrophysics Data System (ADS)

The study and prediction of chemical reactivity is one of the most influential contributions of quantum chemistry. A central concept in the theoretical treatment of chemical reactions is the reaction pathway, which can be quite difficult to integrate accurately and efficiently. This talk will outline our developments in the integration of these pathways on ab initio potential energy surfaces. We will also describe results from recent studies on the kinetics of transition metal catalyzed reactions, including the importance of vibrational coupling to the reaction coordinate and the role of this coupling in catalytic rate enhancement.

Hratchian, Hrant P.

2011-06-01

369

Some thoughts on the muon catalyzed fusion reactor  

SciTech Connect

The design of the muon catalyzed fusion reactor is discussed. Some of the engineering challenges and critical research areas such as ..pi../sup -/ meson transport, beam entry single crystal window and coherent x-ray for stripping the muon from ..cap alpha.. particle, are considered. In order to reduce the tritium inventory and neutron wall loading, use of the laser technique for manipulating the d-t mixture is considered. The heterogeneous d-t mixture using the droplet or jet is discussed. 39 refs., 6 figs.

Takahashi, H.

1986-01-01

370

Palladium- and nickel-catalyzed alkenylation of enolates.  

PubMed

Transition-metal-catalyzed alkenylation of enolates provides a direct method to synthesize broadly useful ?,?-unsaturated carbonyl compounds from the corresponding carbonyl compound and alkenyl halides. Despite being reported in the early seventies, this reaction class saw little development for many years. In the past decade, however, efforts to develop this reaction further have increased considerably, and many research groups have reported efficient coupling protocols, including enantioselective versions. These reactions most commonly employ palladium catalysts, but there are also some important reports using nickel. There are many examples of this powerful transformation being used in the synthesis of complex natural products. PMID:23325616

Ankner, Tobias; Cosner, Casey C; Helquist, Paul

2013-02-01

371

Stereoretentive Copper (II) Catalyzed Ritter Reactions of Secondary Cycloalkanols  

PubMed Central

A Ritter-like coupling reaction of cyclic alcohols and both aryl and alkyl nitriles to form amides catalyzed by copper (II) triflate is described. These reactions proceed in good yields under mild and often solvent-free conditions. With 2- and 3-substituted cycloalkanols, amide products are formed with near complete retention of configuration. This is likely due to fast nucleophilic capture of a non-planar carbocations (hyperconjomers) stabilized by ring hyperconjugation. A critical aspect of this novel catalytic cycle is the in situ activation of the alcohol substrates by thionyl chloride to form chlorosulfites. PMID:24376393

Al-huniti, Mohammed H.

2013-01-01

372

OsO 4-catalyzed amination of silyl enol ethers: enantioselective synthesis of ?-amino ketones  

Microsoft Academic Search

Osmium tetroxide catalyzed asymmetric aminohydroxylation of silyl enol ethers using cinchona alkaloids as chiral ligands and chloramine-T as the nitrogen source affords enantiomerically pure ?-amino ketones.

Prodeep Phukan; A Sudalai

1998-01-01

373

Recombined DNA vaccines encoding calreticulin linked to HPV6bE7 enhance immune response and inhibit angiogenic activity in B16 melanoma mouse model expressing HPV 6bE7 antigen.  

PubMed

Calreticulin (CRT) has been reported to have an effect of upregulating MHC class I presentation as well as inhibiting angiogenesis in vitro and in vivo. Combination of dual mechanisms of enhanced immunogenicity of human papillomavirus (HPV) 6bE7 antigen and antiangiogenesis may be introduced in the strategy of vaccines against condyloma acuminatum (CA) resulting from HPV infection. Therefore, we constructed DNA vaccines by employing different lengths of CRT chimerically linked to a model antigen HPV6bE7 and investigated the immunological and antiangiogenic effects of these vaccines in a B16 melanoma model that express HPV6bE7 antigen. Our results showed that vaccination with CRT180/HPV6bE7 or CRT120/HPV6bE7 enhanced the presence of CD8(+) T cells and TCRgammadelta T cells in vivo, increased the specific lysis activity against E7-expressing cells and secretion levels of IL-2 and IFN-gamma by activating T cells in vitro significantly. Moreover, recombined CRT180 or CRT120 with HPV6bE7 vaccines could elicit a more efficient E7-specific immune response than HPV6bE7 alone. The similarity of immunological enhancement of CRT180/HPV6bE7 and CRT120/HPV6bE7 implies that the immunologically active region mainly exist in fragment 1-120 aa. Furthermore, CRT180/HPV6bE7 and CRT180 displayed remarkable superiority over CRT120/HPV6bE7 in vivo angiogenesis assay, suggesting that the antiangiogenic activity of CRT resides in a domain between aa 120 and 180. Vaccination with CRT180/HPV6bE7 generated the best protective effect of delaying tumor formation and reduction of tumor size in tumor growth inhibition experiment among all DNA constructs. Therefore, CRT180/HPV6bE7 vaccine may enhance the immunological response to HPV6bE7 and inhibit angiogenesis. This construct may be useful in preventing HPV-associated dermatosis and may be developed as a promising strategy to control CA. PMID:16710741

Zhao, Ke-Jia; Cheng, Hao; Zhu, Ke-Jian; Xu, Yan; Chen, Min-Li; Zhang, Xing; Song, Tao; Ye, Jun; Wang, Qi; Chen, Da-Fang

2006-07-01

374

Thermally Induced And Base Catalyzed Reactions Of Naphthoquinone Diazides  

NASA Astrophysics Data System (ADS)

Thermally induced and base catalyzed reactions of a phenol ester of 1,2-naphthoquinone-diazide-5-sulfonic acid (DAM) with p-cresol were investigated. In total seven reaction products were obtained for the thermally induced reaction. The three major products, TR--F4, TR-F6 and TR-F7, were isolated and their structures were determined by means of several advanced spectroscopic techniques like Fourier transform nuclear magnetic resonance (FTNMR) and field desorption mass spectroscopy (FD-MS). Besides a cresol ester of indenecarboxylic acid (TR-F6) and an azo compound which contains two DAM originated moieties and cresol (TR-F7), the formation of a novel compound was found; a phenol ester of 2-cresyl-l-naphthol-5-sulfonic acid. On the other hand, four reaction products were found in the base (a 2.38wt% tetramethylammonium hydroxide aq. solution) catalyzed reaction products of DAM with p-cresol, and two major products, BC-Fl and BC-F3, which appeared at the initial stage of the reaction were isolated. The structure determination of the two major products was carried out in the same manner as described above. It was discovered that BC-Fl was a cresol ester of 1-naphthol while BC-F3 was an azoxy compound. Brief discussions will be made on those reactions of naphthoquinone diazides with a matrix novolak resin with reference to the results obtained by the present study.

Koshiba, Mitsunobu; Murata, Makoto; Matsui, Mariko; Harita, Yoshiyuki

1988-01-01

375

Porous silicon formation during Au-catalyzed etching  

NASA Astrophysics Data System (ADS)

The formation of "black" nano-textured Si during the Au-catalyzed wet-chemical etch process was investigated with respect to photovoltaic applications. Cross-sectional scanning electron microscopy (SEM) images recorded at different stages of the etch process exhibit an evolution of a two-layer structure, consisting of cone-like Si hillocks covered with a nano-porous Si (np-Si) layer. Optical measurements confirm the presence of a np-Si phase which appears after the first ˜10 s of the etch process and continuously increases with the etch time. Furthermore, the etch process was investigated on Si substrates with different doping levels (˜0.01-100 ? cm). SEM images show a transition from the two-layer morphology to a structure consisting entirely of np-Si for higher doping levels (<0.1 ? cm). The experimental results are discussed on the basis of the model of a local electrochemical etch process. A better understanding of the metal-catalyzed etch process facilitates the fabrication of "black" Si on various Si substrates, which is of significant interest for photovoltaic applications.

Algasinger, Michael; Bernt, Maximilian; Koynov, Svetoslav; Stutzmann, Martin

2014-04-01

376

Lipase-catalyzed polyester synthesis--a green polymer chemistry.  

PubMed

This article is a short comprehensive review describing in vitro polyester synthesis catalyzed by a hydrolysis enzyme of lipase, most of which has been developed for these two decades. Polyesters are prepared by repeated ester bond-formation reactions; they include two major modes, ring-opening polymerization (ROP) of cyclic monomers such as cyclic esters (lactones) and condensation polymerization via the reaction between a carboxylic acid or its ester group and an alcohol group. Polyester synthesis is, therefore, a reaction in reverse way of in vivo lipase catalysis of ester bond-cleavage with hydrolysis. The lipase-catalyzed polymerizations show very high chemo-, regio-, and enantio-selectivities and involve various advantageous characteristics. Lipase is robust and compatible with other chemical catalysts, which allows novel chemoenzymatic processes. New syntheses of a variety of functional polyesters and a plausible reaction mechanism of lipase catalysis are mentioned. The polymerization characteristics are of green nature currently demanded for sustainable society, and hence, desirable for conducting 'green polymer chemistry'. PMID:20431260

Kobayashi, Shiro

2010-01-01

377

Enzyme catalyzed electricity-driven water softening system.  

PubMed

Hardness in water, which is caused by divalent cations such as calcium and magnesium ions, presents a major water quality problem. Because hard water must be softened before use in residential applications, there is great interest in the saltless water softening process because, unlike ion exchange softeners, it does not introduce additional ions into water. In this study, a saltless hardness removal driven by bioelectrochemical energy produced through enzymatic oxidation of glucose was proposed and investigated. Glucose dehydrogenase was coated on a carbon electrode to catalyze glucose oxidation in the presence of NAD? as a cofactor/mediator and methylene green as an electrocatalyst. The results showed that electricity generation stimulated hardness removal compared with non-electricity conditions. The enzymatic water softener worked upon a 6h batch operation per day for eight days, and achieved an average hardness removal of 46% at a high initial concentration of 800 mg/L as CaCO?. More hardness was removed at a lower initial concentration. For instance, at 200mg/L as CaCO? the enzymatic water softener removed 76.4±4.6% of total hardness. The presence of magnesium ions decreased hardness removal because of its larger hydrated radius than calcium ions. The enzymatic water softener removed 70-80% of total hardness from three actual hard water samples. These results demonstrated a proof-of-concept that enzyme catalyzed electricity generation can be used to soften hard water. PMID:23040397

Arugula, Mary A; Brastad, Kristen S; Minteer, Shelley D; He, Zhen

2012-12-10

378

An antibody-catalyzed bimolecular Diels-Alder reaction  

SciTech Connect

There exist over 1,500 known enzymes which carry out a vast array of chemical reactions with remarkable specificity and reaction rates. It is surprising then that there are no documented examples of enzyme-catalyzed pericyclic cycloaddition reactions, yet there are among the most powerful and commonly used reactions in synthetic organic chemistry. The most important of these is the Diels-Alder reaction of a diene with a dienophile, which provides a straightforward and highly stereospecific route to cyclohexene derivatives. Given the importance of this reaction in organic chemistry and its novel mechanism, it was of interest to ask whether a Diels-Alderase enzymatic catalyst could be evolved from an antibody combining site. Generation of antibodies to a structure that mimics the pericyclic transition state for a Diels-Alder reaction should result in an antibody combining site that lowers the entropy of activation {Delta}S{sup {double dagger}} by binding both the diene and the dienophile in a reactive conformation. The authors approach toward the design of a transition-state analogue involves incorporation of an ethano bridge, which locks the cyclohexene ring of hapten in a conformation that resembles the proposed pericyclic transition state for the Diels-Alder reaction of cisoid diene with dienophile. The authors now report that antibodies generated to the transition-state analogue catalyze the addition of the acyclic water-soluble diene to the maleimide derivative to give the cyclohexene product.

Braisted, A.C.; Schultz, P.G. (Lawrence Berkeley Laboratory, CA (USA))

1990-09-26

379

Solution-solid-solid mechanism: superionic conductors catalyze nanowire growth.  

PubMed

The catalytic mechanism offers an efficient tool to produce crystalline semiconductor nanowires, in which the choice, state, and structure of catalysts are active research issues of much interest. Here we report a novel solution-solid-solid (SSS) mechanism for nanowire growth catalyzed by solid-phase superionic conductor nanocrystals in low-temperature solution. The preparation of Ag2Se-catalyzed ZnSe nanowires at 100-210 °C is exampled to elucidate the SSS model, which can be extendable to grow other II-VI semiconductor (e.g., CdSe, ZnS, and CdS) nanowires by the catalysis of nanoscale superionic-phase silver or copper(I) chalcogenides (Ag2Se, Ag2S, and Cu2S). The exceptional catalytic ability of these superionic conductors originates from their structure characteristics, known for high-density vacancies and fast mobility of silver or copper(I) cations in the rigid sublattice of Se(2-) or S(2-) ions. Insights into the SSS mechanism are provided based on the formation of solid solution and the solid-state ion diffusion/transport at solid-solid interface between catalyst and nanowire. PMID:23919513

Wang, Junli; Chen, Kangmin; Gong, Ming; Xu, Bin; Yang, Qing

2013-09-11

380

Lipase-catalyzed polyester synthesis - A green polymer chemistry  

PubMed Central

This article is a short comprehensive review describing in vitro polyester synthesis catalyzed by a hydrolysis enzyme of lipase, most of which has been developed for these two decades. Polyesters are prepared by repeated ester bond-formation reactions; they include two major modes, ring-opening polymerization (ROP) of cyclic monomers such as cyclic esters (lactones) and condensation polymerization via the reaction between a carboxylic acid or its ester group and an alcohol group. Polyester synthesis is, therefore, a reaction in reverse way of in vivo lipase catalysis of ester bond-cleavage with hydrolysis. The lipase-catalyzed polymerizations show very high chemo-, regio-, and enantio-selectivities and involve various advantageous characteristics. Lipase is robust and compatible with other chemical catalysts, which allows novel chemo-enzymatic processes. New syntheses of a variety of functional polyesters and a plausible reaction mechanism of lipase catalysis are mentioned. The polymerization characteristics are of green nature currently demanded for sustainable society, and hence, desirable for conducting ‘green polymer chemistry’. PMID:20431260

Kobayashi, Shiro

2010-01-01

381

Ionic Liquid Catalyzed Electrolyte for Electrochemical Polyaniline Supercapacitors  

NASA Astrophysics Data System (ADS)

The effect of different wt.% of ionic liquid "1,6-bis (trimethylammonium-1-yl) hexane tetrafluoroborate" in 0.5 M LiClO4+PC electrolyte on the supercapacitor properties of polyaniline (PANI) thin film are investigated. The PANI film is synthesized using electropolymerization of aniline in the presence of sulfuric acid. The electrochemical properties of the PANI thin film are studied by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) measurements. The optimum amount of the ionic liquid is found to be 2 wt.% which provides better ionic conductivity of the electrolyte. The highest specific capacitance of 259 F/g is obtained using the 2 wt.% electrolyte. This capacitance remains at up to 208 F/g (80% capacity retention) after 1000 charge-discharge cycles at a current density of 0.5 mA/g. The PANI film in the 2 wt.% ionic liquid catalyzed 0.5 M LiClO4+PC electrolyte shows small electrochemical resistance, better rate performance and higher cyclability. The increased ionic conductivity of the 2 wt.% ionic liquid catalyzed electrolyte causes a reduction in resistance at the electrode/electrolyte interface, which can be useful in electrochemically-preferred power devices for better applicability.

Inamdar, A. I.; Im, Hyunsik; Jung, Woong; Kim, Hyungsang; Kim, Byungchul; Yu, Kook-Hyun; Kim, Jin-Sang; Hwang, Sung-Min

2013-05-01

382

Stereoselective palladium-catalyzed carbocyclization of allenic allylic carboxylates.  

PubMed

Palladium(0)-catalyzed reaction of allene-substituted allylic carboxylates 3-8 employing 2-5 mol % of Pd(dba)(2) in refluxing toluene leads to the carbocyclization and elimination of carboxylic acid to give bicyclo[4.3.0]nonadiene and bicyclo[5.3.0]decadiene derivatives (12-17). The carbon-carbon bond formation is stereospecific, occurring syn with respect to the leaving group. Addition of maleic anhydride as a ligand to the above-mentioned procedures changed the outcome of the reaction, and under these conditions 3-5 afforded cycloisomerized products 21-23. The experimental results are consistent with a mechanism involving oxidative addition of the allylic carboxylate to Pd(0) to give an electron-deficient (pi-allyl)palladium intermediate, followed by nucleophilic attack by the allene on the face of the pi-allyl opposite to that of the palladium atom. Furthermore, it was found that the Pd(dba)(2)-catalyzed cyclization of the trans-cycloheptene derivative (trans-8) can be directed to give either the trans-fused (trans-17) or the cis-fused (cis-17) ring system by altering the solvent. The former reaction proceeds via a nucleophilic trans-allene attack on the (pi-allyl)palladium intermediate, whereas the latter involves a syn-allene insertion into the allyl-Pd bond of the same intermediate. The products from the carbocylization undergo stereoselective Diels-Alder reactions to give stereodefined polycyclic systems in high yields. PMID:14611252

Franzén, Johan; Löfstedt, Joakim; Falk, Jennica; Bäckvall, Jan-E

2003-11-19

383

Self-regulated pulsed nucleation in catalyzed nanowire growth  

NASA Astrophysics Data System (ADS)

We present a theoretical analysis of catalyzed nanowire growth based on the material balance in a droplet within one monolayer growth cycle. Pulsed supersaturation and nucleation probability density are shown to originate from the material balance under rather general assumptions. We calculate explicitly the time-dependent nucleation probability as a function of nanowire radius and growth conditions. For small nanowire radii, the timescale hierarchy of different growth steps is demonstrated, leading to a temporal anticorrelation of nucleation events. Numerical analysis is performed in the case of Au-catalyzed GaAs nanowires, where the nucleation probabilities are mapped out as functions of nanowire radius at different conditions. The transition from deltalike to Poissonian temporal distribution of nucleation events is discussed depending on relevant parameters. We speculate that the self-regulated narrowing of nucleation probabilities suppresses random broadening of nanowire length distributions. This focusing effect is specific for nucleation in nanovolumes and might be used for tailoring the size spectra of different nano-objects.

Dubrovskii, V. G.

2013-05-01

384

Chloride-catalyzed corrosion of plutonium in glovebox atmospheres  

SciTech Connect

Characterization of glovebox atmospheres and the black reaction product formed on plutonium surfaces shows that the abnormally rapid corrosion of components in the fabrication line is consistent with a complex salt-catalyzed reaction involving gaseous hydrogen chloride (HCl) and water. Analytical data verify that chlorocarbon and HCl vapors are presented in stagnant glovebox atmospheres. Hydrogen chloride concentrations approach 7 ppm at some locations in the glovebox line. The black corrosion product is identified as plutonium monoxide monohydride (PuOH), a product formed by hydrolysis of plutonium in liquid water and salt solutions at room temperature. Plutonium trichloride (PuCl{sub 3}) produced by reaction of HCl at the metal surface is deliquescent and apparently forms a highly concentrated salt solution by absorbing moisture from the glovebox atmosphere. Rapid corrosion is attributed to the ensuing salt-catalyzed reaction between plutonium and water. Experimental results are discussed, possible involvement of hydrogen fluoride (HF) is examined, and methods of corrective action are presented in this report.

Burgess, M. [ed.; Haschke, J.M.; Allen, T.H.; Morales, L.A.; Jarboe, D.M.; Puglisi, C.V.

1998-04-01

385

Pd-catalyzed cross-coupling reactions of alkyl halides.  

PubMed

Cross-coupling reactions have become indispensable tools for creating carbon-carbon (or heteroatom) bonds in organic synthesis. Like in other important transition metal catalyzed reactions, such as metathesis, addition, and polymerization, unsaturated compounds are usually employed as substrates for cross-coupling reactions. However during the past decade, a great deal of effort has been devoted to the use of alkyl halides as saturated compounds in cross-coupling reactions, which has resulted in significant progress in this undeveloped area by introducing new effective ligands. Many useful catalytic systems are now available for synthetic transformations based on C(sp(3))-C(sp(3)), C(sp(3))-C(sp(2)) and C(sp(3))-C(sp) bond formation as complementary methods to conventional C(sp(2))-C(sp(2)), C(sp(2))-C(sp) and C(sp)-C(sp) coupling. This tutorial review summarizes recent advances in cross-coupling reactions of alkyl halides and pseudohalides catalyzed by a palladium complex. PMID:21785791

Kambe, Nobuaki; Iwasaki, Takanori; Terao, Jun

2011-10-01

386

Muon-catalyzed fusion: a new direction in fusion research  

SciTech Connect

In four years of intensive research, muon-catalyzed fusion has been raised from the level of a scientific curiosity to a potential means of achieving clean fusion energy. This novel approach to fusion is based on the fact that a sub-atomic particle known as a ''muon'' can induce numerous energy-releasing fusion reactions without the need for high temperatures or plasmas. Thus, the muon serves as a catalyst to facilitate production for fusion energy. The success of the research effort stems from the recent discovery of resonances in the reaction cycle which make the muon-induced fusion process extremely efficient. Prior estimates were pessimistic in that only one fusion per muon was expected. In that case energy balance would be impossible since energy must be invested to generate the muons. However, recent work has gone approximately half-way to energy balance and further improvements are being worked on. There has been little time to assess the full implications of these discoveries. However, various ways to use muon-catalyzed fusion for electrical power production are now being explored.

Jones, S.E.

1986-01-01

387

Thermodynamics of Enzyme-Catalyzed Reactions: Part 7--2007 Update Robert N. Goldberg,a...  

E-print Network

Thermodynamics of Enzyme-Catalyzed Reactions: Part 7--2007 Update Robert N. Goldberg,a... Yadu B evaluations of equilibrium constants and enthalpy changes for enzyme-catalyzed reactions. For each reaction, the following information is given: the reference for the data, the reaction studied, the name of the enzyme

Magee, Joseph W.

388

Monitoring Enzyme-catalyzed Reactions in Micromachined Nanoliter Wells using a Conventional Microscope based  

E-print Network

Monitoring Enzyme-catalyzed Reactions in Micromachined Nanoliter Wells using a Conventional to ethanol and carbon dioxide. This pathway consists of 12 enzyme-catalyzed reactions. With the approach � 300µm2 . The depth varies from 20 to 50µm. Enzyme activity levels can be derived by monitoring

van Vliet, Lucas J.

389

Chiral Proline-Based Ligands for Iridium-Catalyzed Asymmetric Hydrogenation  

E-print Network

Chiral Proline-Based Ligands for Iridium-Catalyzed Asymmetric Hydrogenation Inauguraldissertation. Parts of this work have been previously published: ,,Proline-Based P,O Ligands/Iridium Complexes in Iridium-Catalyzed Asymmetric Hydrogenation: New Catalysts, Substrates and Applications in Total Synthesis

Amrhein, Valentin

390

ELECTRIC DRIVE BY `25: How California Can Catalyze Mass Adoption of  

E-print Network

deployment and the resulting reduction in air pollution from GHFUHDVHG SHWUROHXP XVDJH FDQ VDYH WKH VWDWHELECTRIC DRIVE BY `25: How California Can Catalyze Mass Adoption of Electric Vehicles by 2025@law.berkeley.edu. #12;1UCLA Law \\ Berkeley Law ELECTRIC DRIVE BY `25: How California Can Catalyze Mass Adoption

Kammen, Daniel M.

391

Palladium catalyzed 1,8-conjugate addition to heptafulvene via bis-?-allyl palladium complexes.  

PubMed

The palladium catalyzed 1,8-conjugate addition of heptafulvene, an antiaromatic conjugated 8?-electron system, is discussed. The method is utilized for the concise synthesis of bis-functionalized cycloheptatriene (CHT) derivatives. This is the first report on the palladium catalyzed bisfunctionalization of a cyclic cross conjugated system. PMID:21899322

George, Sholly Clair; Thulasi, Sreeja; Anas, S; Radhakrishnan, K V; Yamamoto, Yoshinori

2011-10-01

392

Palladium-Catalyzed Intramolecular Carbopalladation/Cyclization Cascade: Access to Polycyclic N-Fused Heterocycles  

PubMed Central

An efficient palladium-catalyzed intramolecular carbopalladation/cyclization cascade toward tetra- and pentacyclic N-fused heterocycles has been developed. This transformation proceeds via the palladium-catalyzed coupling of aryl halides with internal propargylic esters or ethers followed by the 5-endo-dig cyclization leading to polycyclic pyrroloheterocycles in moderate to excellent yields. PMID:21058673

Chernyak, Dmitri

2011-01-01

393

Synthetic Methods Gold(i)-Catalyzed 5-endo-dig Carbocyclization of  

E-print Network

have recently demonstrated that cationic gold(i) complexes catalyze the Conia­ene reaction by a mechanism that appears to involve formation of a gold(i) alkyne complex.[11] Thus, we reasonedSynthetic Methods Gold(i)-Catalyzed 5-endo-dig Carbocyclization of Acetylenic Dicarbonyl Compounds

Toste, Dean

394

Au-catalyzed isomerization of cyclopropenes: a novel approach to indene derivatives  

E-print Network

- atives in high yields. The reaction is suggested to proceed through gold vinyl carbenoid intermediate. � or thermolysis. Transition-metal complexes can promote or catalyze the isomeri- zation under relatively mild.4 h or ð1� M M M ð2� On the other hand, gold-catalyzed organic reactions have been extensively

Wang, Jianbo

395

Total synthesis of (-)-kaitocephalin based on a Rh-catalyzed C-H amination.  

PubMed

A total synthesis of (-)-kaitocephalin, an ionotropic glutamate receptor antagonist, is accomplished in highly stereocontrolled manner via Overman rearrangement, rhodium-catalyzed benzylic C-H amination, pyrrolidine formation involving nucleophilic opening of a cyclic sulfamate, and rhodium-catalyzed allylic C-H amination as key steps. PMID:22390213

Takahashi, Keisuke; Yamaguchi, Daisuke; Ishihara, Jun; Hatakeyama, Susumi

2012-03-16

396

Synthesis of Functionalized Cyclohexenone Core of Welwitindolinones via Rhodium- Catalyzed [5+1] Cycloaddition  

PubMed Central

The cyclohexenone core of welwitindolinones was synthesized by a Rh(I)-catalyzed [5+1]-cycloaddition of an allenylcyclopropane with CO. A penta-substituted cyclopropane was prepared successfully by a Rh(II)-catalyzed intramolecular cyclopropanation of alkenes with chlorodiazoacetates. PMID:22783971

Zhang, Min

2012-01-01

397

~ristalsof bovine chyrnotrypsin. Enzymes are proteins specialized to catalyze biological reac-  

E-print Network

Figure 8-1 ~ristalsof bovine chyrnotrypsin. 1 Enzymes are proteins specialized to catalyze of biochemistry is the history of en- zyme research. The name enzyme ("in yeast") was not used until 1877- furic acid. Although Louis Pasteur recognized that fermentation is catalyzed by enzymes, he postulated

Vallino, Joseph J.

398

Palladium-catalyzed intramolecular carbopalladation/cyclization cascade: access to polycyclic N-fused heterocycles.  

PubMed

An efficient palladium-catalyzed intramolecular carbopalladation/cyclization cascade toward tetra- and pentacyclic N-fused heterocycles has been developed. This transformation proceeds via the palladium-catalyzed coupling of aryl halides with internal propargylic esters or ethers followed by the 5-endo-dig cyclization leading to polycyclic pyrroloheterocycles in moderate to excellent yields. PMID:21058673

Chernyak, Dmitri; Gevorgyan, Vladimir

2010-12-01

399

Alkene epoxidation catalyzed by cytochrome P450 BM-3 139-3 Edgardo T. Farinas,  

E-print Network

Catalyzing a wide range of oxidative reactions under mild conditions in aqueous solutions, cytochrome P450Alkene epoxidation catalyzed by cytochrome P450 BM-3 139-3 Edgardo T. Farinas, Miguel Alcalde conversion of cytochrome P450 BM-3, a medium-chain (C12 ­C18) fatty acid monooxygenase, into a highly

Arnold, Frances H.

400

Helium Catalyzed D-D Fusion in a Levitated Dipole J. Kesner, D.T. Garnier  

E-print Network

Helium Catalyzed D-D Fusion in a Levitated Dipole J. Kesner, D.T. Garnier , A. Hansen , M. Mauel catalyzed D-D". The D-D cycle is difficult in a traditional fusion confinement device such as a tokamak

401

Copper-catalyzed aerobic oxidative synthesis of aryl nitriles from benzylic alcohols and aqueous ammonia.  

PubMed

Copper-catalyzed direct conversion of benzylic alcohols to aryl nitriles was realized using NH3(aq.) as the nitrogen source, O2 as the oxidant and TEMPO as the co-catalyst. Furthermore, copper-catalyzed one-pot synthesis of primary aryl amides from alcohols was also achieved. PMID:23563148

Tao, Chuanzhou; Liu, Feng; Zhu, Youmin; Liu, Weiwei; Cao, Zhiling

2013-05-28

402

Atmospheric Environment 40 (2006) 68636878 Acid-catalyzed reactions of hexanal on sulfuric acid particles  

E-print Network

Atmospheric Environment 40 (2006) 6863­6878 Acid-catalyzed reactions of hexanal on sulfuric acid are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds into acidic aerosols. In the present study, we use the aerodyne aerosol mass spectrometer (AMS) to probe

Elrod, Matthew J.

403

Mathematical Analysis of Activation Thresholds in EnzymeCatalyzed Positive Feedbacks: Application  

E-print Network

angiotensin is produced from angiotensinogen by the proteolytic enzyme renin; fibrinolysis, which providesMathematical Analysis of Activation Thresholds in Enzyme­Catalyzed Positive Feedbacks: Application A hierarchy of enzyme­catalyzed positive feedback loops is examined by mathematical and numerical analysis

New York at Stoney Brook, State University of

404

Kinetic Investigation of the Inhibitory Effect of Gemcitabine on DNA Polymerization Catalyzed by Human Mitochondrial  

E-print Network

Kinetic Investigation of the Inhibitory Effect of Gemcitabine on DNA Polymerization CatalyzedCellandMolecularBiology,DepartmentofChemistryandBiochemistry, UniversityofTexas,Austin, Texas 78712 Gemcitabine, 2 -deoxy-2 ,2 -difluorocytidine (dFdC), is a drug approved gemcitabine interferes with mitochondrial DNA replication catalyzed by human DNA polymerase . Here we employed

Suo, Zucai

405

Anthracene-Induced Turnover Enhancement in the Manganese Porphyrin-Catalyzed Epoxidation of Olefins  

E-print Network

Anthracene-Induced Turnover Enhancement in the Manganese Porphyrin-Catalyzed Epoxidation of Olefins of the manganese porphyrin. Introduction We have been exploring the notion that reversible supra- molecular complex) catalyzed by achiral manganese porphyrins and by optically active manganese(salicyl)diamine complexes

406

Palladium-catalyzed carbonylation of o-iodoanilines for synthesis of isatoic anhydrides.  

PubMed

A novel palladium-catalyzed oxidative double carbonylation of o-iodoanilines for the synthesis of isatoic anhydrides has been developed. The reaction employs readily available o-iodoanilines as the starting materials and proceeds under mild conditions. For extension, palladium-catalyzed oxidative carbonylation of anthranilic acids was developed for the synthesis of substituted isatoic anhydrides in high to excellent yields. PMID:24720706

Gao, Sha; Chen, Ming; Zhao, Mi-Na; Du, Wei; Ren, Zhi-Hui; Wang, Yao-Yu; Guan, Zheng-Hui

2014-05-01

407

4844 Biochemistry 1991, 30, 4844-4854 Ribozyme-Catalyzed and Nonenzymatic Reactions of Phosphate  

E-print Network

nucleophilic substitution reactions of the phosphate diester, methyl 2,4-dinitrophenylphosphate monoanion4844 Biochemistry 1991, 30, 4844-4854 Ribozyme-Catalyzed and Nonenzymatic Reactions of Phosphate of Tetrahymena thermophila pre-rRNA catalyzes a guanosine-dependent endonuclease reaction that is analogous

Herschlag, Dan

408

Time-dependent kinetic complexities in cholinesterase-catalyzed reactions.  

PubMed

Cholinesterases (ChEs) display a hysteretic behavior with certain substrates and inhibitors. Kinetic cooperativity in hysteresis of ChE-catalyzed reactions is characterized by a lag or burst phase in the approach to steady state. With some substrates damped oscillations are shown to superimpose on hysteretic lags. These time dependent peculiarities are observed for both butyrylcholinesterase and acetylcholinesterase from different sources. Hysteresis in ChE-catalyzed reactions can be interpreted in terms of slow transitions between two enzyme conformers E and E'. Substrate can bind to E and/or E', both Michaelian complexes ES and ?'S can be catalytically competent, or only one of them can make products. The formal reaction pathway depends on both the chemical structure of the substrate and the type of enzyme. In particular, damped oscillations develop when substrate exists in different, slowly interconvertible, conformational, and/or micellar forms, of which only the minor form is capable of binding and reacting with the enzyme. Biphasic pseudo-first-order progressive inhibition of ChEs by certain carbamates and organophosphates also fits with a slow equilibrium between two reactive enzyme forms. Hysteresis can be modulated by medium parameters (pH, chaotropic and kosmotropic salts, organic solvents, temperature, osmotic pressure, and hydrostatic pressure). These studies showed that water structure plays a role in hysteretic behavior of ChEs. Attempts to provide a molecular mechanism for ChE hysteresis from mutagenesis studies or crystallographic studies failed so far. In fact, several lines of evidence suggest that hysteresis is controlled by the conformation of His438, a key residue in the catalytic triad of cholinesterases. Induction time may depend on the probability of His438 to adopt the operative conformation in the catalytic triad. The functional significance of ChE hysteresis is puzzling. However, the accepted view that proteins are in equilibrium between preexisting functional and non-functional conformers, and that binding of a ligand to the functional form shifts equilibrium towards the functional conformation, suggests that slow equilibrium between two conformational states of these enzymes may have a regulatory function in damping out the response to certain ligands and irreversible inhibitors. This is particularly true for immobilized (membrane bound) enzymes where the local substrate and/or inhibitor concentrations depend on influx in crowded organellar systems, e.g. cholinergic synaptic clefts. Therefore, physiological or toxicological relevance of the hysteretic behavior and damped oscillations in ChE-catalyzed reactions and inhibition cannot be ruled out. PMID:23157295

Masson, P

2012-10-01

409

Electrostatic effects on the rates of DNA-catalyzed reactions  

NASA Astrophysics Data System (ADS)

Diol-epoxide metabolites of many genotoxic polycyclic aromatic hydrocarbons are hydrolyzed to tetraols in a detoxification reaction. The hydrolysis reaction has both spontaneous and acid-catalyzed components; moreover, the reaction rate increases in the presence of DNA. The best studied of these diol epoxide metabolites are the trans 7,8 diol-9,10 epoxides of benzo[a]pyrene: anti-BPDE, the proximate carcinogen, in which the oxirane ring is anti with respect to the 7-hydroxyl group, and its syn diastereomer, syn-BPDE. Jerina and coworkers have studied the kinetics of the hydrolysis of syn- and anti-BPDE as a function of pH and DNA concentration and have measured the equilibrium constant for the formation of a noncovalent complex with DNA. They constructed a two-state model in which the diol epoxide is either free or statically bound: the free fraction is hydrolyzed with the same kinetics as it exhibits in solution without DNA; the bound diol epoxide reacts at faster rates. In this model, the dependence of the observed hydrolysis rates on both DNA concentration and pH is explained by using the rate constants, k0 and kH, for reactions of the free diol epoxide, the rate constants, kcat0 and kcatH, for the bound molecule, and the binding constant, Keq. The present work uses an acidic-domain interpretation of the two-state model to explain the catalytic effect of DNA on the acid-catalyzed hydrolysis of syn- and anti-BPDE. Postulating that the rate enhancement is a result of acidic domains at the DNA surface, we assumed the relationship k catH = k H [H +] b, where [H +] b is the hydrogen ion concentration near the bound molecule. Using numerical solutions to the Poisson-Boltzmann equation, the pH dependence of acidic domains at the surface of the polyelectrolyte, DNA, was calculated. Energy-minimization calculations were used to estimate the conformations of diol epoxide-DNA intercalation complexes. Poisson-Boltzmann (PB) calculations on these structures yielded hydrogen-ion concentrations near the epoxide group consistent with the k catH/k H ratio over a range of added-salt concentrations. The results strongly suggest that DNA catalysis of diol-epoxide hydrolysis is a polyelectrolyte effect. The mechanisms and rate constants observed for the acid-catalyzed hydrolysis in the absence of DNA are consistent with the increase in the rate constant induced by DNA. It may be concluded that the catalysis is primarily an effect of the acidic domains in the surface grooves of the nucleic acid.

Pack, George R.; Wong, Linda

1996-04-01

410

Degradation and transformation of atrazine under catalyzed ozonation process with TiO2 as catalyst.  

PubMed

Degradation of atrazine by heterogeneously catalyzed ozonation was carried out with TiO2 in the form of rutile as the catalyst. Some experimental factors such as catalyst dose, ozone dose and initial concentration of atrazine were investigated for their influence on catalyzed ozonation process. Although atrazine was effectively removed from aqueous solution by catalyzed ozonation process, the mineralization degree only reached 56% at the experimental conditions. Five transformation products were identified by GC/MS analysis. The degradation of atrazine involved de-alkylation, de-chlorination and de-amination. Diaminotriazine and 5-azauracil were the de-chlorinated and de-aminated products, respectively. The evolution of concentration of transformation products during catalyzed ozonation process was compared with uncatalyzed ozonation to show the degradation pathway. Toxicity tests based on the inhibition of the luminescence emitted by Vibrio fisheri indicated the detoxification of atrazine by catalyzed ozonation. PMID:25106044

Yang, Yixin; Cao, Hongbin; Peng, Pai; Bo, Hongmiao

2014-08-30

411

Metal-catalyzed living radical polymerization and radical polyaddition for precision polymer synthesis  

NASA Astrophysics Data System (ADS)

The metal-catalyzed radical addition reaction can be evolved into two different polymerization mechanisms, i.e.; chain- and step-growth polymerizations, while both the polymerizations are based on the same metal-catalyzed radical formation reaction. The former is a widely employed metal-catalyzed living radical polymerization or atom transfer radical polymerization of common vinyl monomers, and the latter is a novel metal-catalyzed radical polyaddition of designed monomer with an unconjugated C=C double bond and a reactive C-Cl bond in one molecule. The simultaneous ruthenium-catalyzed living radical polymerization of methyl acrylate and radical polyaddition of 3-butenyl 2-chloropropionate was achieved with Ru(Cp*)Cl(PPh3)2 to afford the controlled polymers, in which the homopolymer segments with the controlled chain length were connected by the ester linkage.

Mizutani, M.; Satoh, K.; Kamigaito, M.

2009-08-01

412

Nickel-catalyzed reductive coupling reactions of 1,6-enynes and the total synthesis of (+)-acutiphycin  

E-print Network

Nickel-Catalyzed Reductive Coupling Reactions of Aldehydes and Chiral 1,6-Enynes. A study of nickel-catalyzed reductive coupling reactions of aldehydes and chiral 1,6-enynes has provided evidence for stereospecific ligand ...

Moslin, Ryan Thomas McLeod

2007-01-01

413

Nickel-catalyzed asymmetric cross-couplings of secondary allylic chlorides and planar-chiral compounds in asymmetric synthesis  

E-print Network

In Part I, nickel-catalyzed asymmetric carbon-carbon bond-forming reactions are described. A nickel/Pybox system effectively catalyzes regio- and enantioselective cross-couplings between racemic secondary allylic chlorides ...

Son, Sunghee

2008-01-01

414

Structural control of cytochrome P450-catalyzed ?-hydroxylation  

PubMed Central

The regiospecific or preferential ?-hydroxylation of hydrocarbon chains is thermodynamically disfavored because the ease of C-H bond hydroxylation depends on the bond strength, and the primary C-H bond of a terminal methyl group is stronger than the secondary or tertiary C-H bond adjacent to it. The hydroxylation reaction will therefore occur primarily at the adjacent secondary or tertiary C-H bond unless the protein structure specifically enforces primary C-H bond oxidation. Here we review the classes of enzymes that catalyze ?-hydroxylation and our current understanding of the structural features that promote the ?-hydroxylation of unbranched and methyl-branched hydrocarbon chains. The evidence indicates that steric constraints are used to favor reaction at the ?-site rather than at the more reactive (?-1)-site. PMID:20727847

Johnston, Jonathan B.; Ouellet, Hugues; Podust, Larissa M.; Ortiz de Montellano, Paul R.

2010-01-01

415

Laccase-catalyzed oxidative polymerization of phenolic compounds.  

PubMed

Enzymatic polymerization of phenolic compounds (catechol, resorcinol, and hydroquinone) was carried out using laccase. The mechanism of polymerization and the structures of the polymers were evaluated in terms of UV-Vis and Fourier transform infrared spectroscopy. The molecular weights of the produced polyphenols were determined with GPC. The results showed that the phenolic monomers firstly turned into quinone intermediates by laccase catalysis. Through further oxidation, the intermediates formed covalent bonds. Finally, catechol units were linked together with ether bonds, and both resorcinol and hydroquinone units were linked together with C-C bonds. The number-average molecular weights of the polyphenols ranged from 1,000 to 1,400 Da (corresponding to the degree of polymerization that varied from 10 to 12) with a lower polydispersity value of about 1.10, showing selective polymerization of phenolic compounds catalyzed by laccase. PMID:23996120

Sun, Xuejiao; Bai, Rubing; Zhang, Ya; Wang, Qiang; Fan, Xuerong; Yuan, Jiugang; Cui, Li; Wang, Ping

2013-12-01

416

Ruthenium-catalyzed reduction of carbon dioxide to formaldehyde.  

PubMed

Functionalization of CO2 is a challenging goal and precedents exist for the generation of HCOOH, CO, CH3OH, and CH4 in mild conditions. In this series, CH2O, a very reactive molecule, remains an elementary C1 building block to be observed. Herein we report the direct observation of free formaldehyde from the borane reduction of CO2 catalyzed by a polyhydride ruthenium complex. Guided by mechanistic studies, we disclose the selective trapping of formaldehyde by in situ condensation with a primary amine into the corresponding imine in very mild conditions. Subsequent hydrolysis into amine and a formalin solution demonstrates for the first time that CO2 can be used as a C1 feedstock to produce formaldehyde. PMID:24605761

Bontemps, Sébastien; Vendier, Laure; Sabo-Etienne, Sylviane

2014-03-19

417

Solvent effects in Acid-catalyzed biomass conversion reactions.  

PubMed

Reaction kinetics were studied to quantify the effects of polar aprotic organic solvents on the acid-catalyzed conversion of xylose into furfural. A solvent of particular importance is ?-valerolactone (GVL), which leads to significant increases in reaction rates compared to water in addition to increased product selectivity. GVL has similar effects on the kinetics for the dehydration of 1,2-propanediol to propanal and for the hydrolysis of cellobiose to glucose. Based on results obtained for homogeneous Brønsted acid catalysts that span a range of pKa values, we suggest that an aprotic organic solvent affects the reaction kinetics by changing the stabilization of the acidic proton relative to the protonated transition state. This same behavior is displayed by strong solid Brønsted acid catalysts, such as H-mordenite and H-beta. PMID:25214063

Mellmer, Max A; Sener, Canan; Gallo, Jean Marcel R; Luterbacher, Jeremy S; Alonso, David Martin; Dumesic, James A

2014-10-27

418

Acid-catalyzed reactions of epoxides for atmospheric nanoparticle growth.  

PubMed

Although new particle formation accounts for about 50% of the global aerosol production in the troposphere, the chemical species and mechanism responsible for the growth of freshly nucleated nanoparticles remain largely uncertain. Here we show large size growth when sulfuric acid nanoparticles of 4-20 nm are exposed to epoxide vapors, dependent on the particle size and relative humidity. Composition analysis of the nanoparticles after epoxide exposure reveals the presence of high molecular weight organosulfates and polymers, indicating the occurrence of acid-catalyzed reactions of epoxides. Our results suggest that epoxides play an important role in the growth of atmospheric newly nucleated nanoparticles, considering their large formation yields from photochemical oxidation of biogenic volatile organic compounds. PMID:25338124

Xu, Wen; Gomez-Hernandez, Mario; Guo, Song; Secrest, Jeremiah; Marrero-Ortiz, Wilmarie; Zhang, Annie L; Zhang, Renyi

2014-11-01

419

Mechanistic investigations of the rhodium catalyzed propargylic CH activation.  

PubMed

Previously we reported the redox-neutral atom economic rhodium catalyzed coupling of terminal alkynes with carboxylic acids using the DPEphos ligand. We herein present a thorough mechanistic investigation applying various spectroscopic and spectrometric methods (NMR, in situ-IR, ESI-MS) in combination with DFT calculations. Our findings show that in contrast to the originally proposed mechanism, the catalytic cycle involves an intramolecular protonation and not an oxidative insertion of rhodium in the OH bond of the carboxylic acid. A ?-allyl complex was identified as the resting state of the catalytic transformation and characterized by X-ray crystallographic analysis. By means of ESI-MS investigations we were able to detect a reactive intermediate of the catalytic cycle. PMID:24377792

Gellrich, Urs; Meißner, Antje; Steffani, Alberto; Kähny, Matthias; Drexler, Hans-Joachim; Heller, Detlef; Plattner, Dietmar A; Breit, Bernhard

2014-01-22

420

Trypsin-catalyzed oxygen-18 labeling for quantitative proteomics  

SciTech Connect

Stable isotope labeling based on relative peptide/protein abundance measurements is commonly applied for quantitative proteomics. Recently, trypsin-catalyzed oxygen-18 labeling has grown in popularity due to its simplicity, cost-effectiveness, and its ability to universally label peptides with high sample recovery. In (18)O labeling, both C-terminal carboxyl group atoms of tryptic peptides can be enzymatically exchanged with (18)O, thus providing the labeled peptide with a 4 Da mass shift from the (16)O-labeled sample. Peptide (18)O labeling is ideally suited for generating a labeled "universal" reference sample used for obtaining accurate and reproducible quantitative measurements across large number of samples in quantitative discovery proteomics.

Qian, Weijun; Petritis, Brianne O.; Nicora, Carrie D.; Smith, Richard D.

2011-07-01

421

The role of fluoride in montmorillonite-catalyzed RNA synthesis.  

PubMed

The montmorillonite-catalyzed reactions of the 5'-phosphorimidazolide of adenosine in the presence of fluoride were investigated to complete our study on the effect of salts on this type of reaction. Both anions and cations have been found to influence the oligomerization reactions of the activated nucleotides, being used here as a model system for pre-biotic RNA synthesis. However, in total contrast to the behavior of the activated nucleotides in the presence of montmorillonite and other salts, alkali metal fluorides did not yield any detectable oligomerization products except in very dilute (<0.005 M) solutions of fluoride. Instead, 5'-phosphorofluoridates were formed. Their identity was confirmed by a combination of HPLC, mass spectrometry, synthesis, and NMR. PMID:24756181

Aldersley, Michael F; Joshi, Prakash C

2014-05-01

422

Synthesis of Rosin Acid Starch Catalyzed by Lipase  

PubMed Central

Rosin, an abundant raw material from pine trees, was used as a starting material directly for the synthesis of rosin acid starch. The esterification reaction was catalyzed by lipase (Novozym 435) under mild conditions. Based on single factor experimentation, the optimal esterification conditions were obtained as follows: rosin acid/anhydrous glucose unit in the molar ratio 2?:?1, reaction time 4?h at 45°C, and 15% of lipase dosage. The degree of substitution (DS) reaches 0.098. Product from esterification of cassava starch with rosin acid was confirmed by FTIR spectroscopy and iodine coloration analysis. Scanning electron microscopy and X-ray diffraction analysis showed that the morphology and crystallinity of the cassava starch were largely destroyed. Thermogravimetric analysis indicated that thermal stability of rosin acid starch decreased compared with native starch. PMID:24977156

Lin, Rihui; Li, He; Long, Han; Su, Jiating; Huang, Wenqin

2014-01-01

423

Amine-catalyzed direct photoarylation of unactivated arenes.  

PubMed

Constructing biaryls through direct aromatic C-H functionalization of unactivated arenes has become a popular topic in organic chemistry. Many efficient methods have been developed. In this Communication, a direct arylation of unactivated arenes with a broad range of aryl iodides is reported. This reaction proceeds through a new type of amine-catalyzed single electron transfer initiated radical coupling procedure to form biaryls in high yields under UV irradiation at room temperature. Only 20?mol% of TMEDA is used as the catalyst. No other additives are required for this transformation, thus avoiding the use of toxic transition metal catalysts, strong bases, or large amounts of other organic additives. This greener protocol provides a new strategy to achieve direct aromatic C-H functionalization and offers a new example of cost-effective and environmentally benign access to biaryls. PMID:24288232

Zheng, Xingliang; Yang, Luo; Du, Weiyuan; Ding, Aishun; Guo, Hao

2014-02-01

424

Cytochromes P450 Catalyze the Reduction of ?,?-Unsaturated Aldehydes  

PubMed Central

The metabolism of ?,?-unsaturated aldehydes, e.g. 4-hydroxynonenal, involves oxidation to carboxylic acids, reduction to alcohols, and glutathionylation to eventually form mercapturide conjugates. Recently we demonstrated that P450s can oxidize aldehydes to carboxylic acids, a reaction previously thought to involve aldehyde dehydrogenase. When recombinant cytochrome P450 3A4 was incubated with 4-hydroxynonenal, O2, and NADPH, several products were produced, including 1,4-dihydroxynonene (DHN), 4-hydroxy-2-nonenoic acid (HNA), and an unknown metabolite. Several P450s catalyzed the reduction reaction in the order (human) P450 2B6 ? P450 3A4 > P450 1A2 > P450 2J2 > (mouse) P450 2c29. Other P450s did not catalyze the reduction reaction (human P450 2E1 & rabbit P450 2B4). Metabolism by isolated rat hepatocytes showed that HNA formation was inhibited by cyanamide, while DHN formation was not affected. Troleandomycin increased HNA production 1.6-fold while inhibiting DHN formation, suggesting that P450 3A11 is a major enzyme involved in rat hepatic clearance of 4-HNE. A fluorescent assay was developed using 9-anthracenealdehyde to measure both reactions. Feeding mice diet containing t-butylated hydroxyanisole increased the level of both activities with hepatic microsomal fractions, but not proportionally. Miconazole (0.5 mM) was a potent inhibitor of these microsomal reduction reactions, while phenytoin and ?-naphthoflavone (both at 0.5 mM) were partial inhibitors, suggesting the role of multiple P450 enzymes. The oxidative metabolism of these aldehydes was inhibited >90% in an Ar or CO atmosphere, while the reductive reactions were not greatly affected. These results suggest that P450s are significant catalysts of reduction of ?,?-unsaturated aldehydes in liver. PMID:21766881

Amunom, Immaculate; Dieter, Laura J.; Tamasi, Viola; Cai, Jan; Conklin, Daniel J.; Srivastava, Sanjay; Martin, Martha V.; Guengerich, F. Peter; Prough, Russell A.

2011-01-01

425

Cytochromes P450 catalyze the reduction of ?,?-unsaturated aldehydes.  

PubMed

The metabolism of ?,?-unsaturated aldehydes, e.g., 4-hydroxynonenal, involves oxidation to carboxylic acids, reduction to alcohols, and glutathionylation to eventually form mercapturide conjugates. Recently, we demonstrated that P450s can oxidize aldehydes to carboxylic acids, a reaction previously thought to involve aldehyde dehydrogenase. When recombinant cytochrome P450 3A4 was incubated with 4-hydroxynonenal, O(2), and NADPH, several products were produced, including 1,4-dihydroxynonene (DHN), 4-hydroxy-2-nonenoic acid (HNA), and an unknown metabolite. Several P450s catalyzed the reduction reaction in the order (human) P450 2B6 ? P450 3A4 > P450 1A2 > P450 2J2 > (mouse) P450 2c29. Other P450s did not catalyze the reduction reaction (human P450 2E1 and rabbit P450 2B4). Metabolism by isolated rat hepatocytes showed that HNA formation was inhibited by cyanamide, while DHN formation was not affected. Troleandomycin increased HNA production 1.6-fold while inhibiting DHN formation, suggesting that P450 3A11 is a major enzyme involved in rat hepatic clearance of 4-HNE. A fluorescent assay was developed using 9-anthracenealdehyde to measure both reactions. Feeding mice a diet containing t-butylated hydroxyanisole increased the level of both activities with hepatic microsomal fractions but not proportionally. Miconazole (0.5 mM) was a potent inhibitor of these microsomal reduction reactions, while phenytoin and ?-naphthoflavone (both at 0.5 mM) were partial inhibitors, suggesting the role of multiple P450 enzymes. The oxidative metabolism of these aldehydes was inhibited >90% in an Ar or CO atmosphere, while the reductive reactions were not greatly affected. These results suggest that P450s are significant catalysts of the reduction of ?,?-unsaturated aldehydes in the liver. PMID:21766881

Amunom, Immaculate; Dieter, Laura J; Tamasi, Viola; Cai, Jian; Conklin, Daniel J; Srivastava, Sanjay; Martin, Martha V; Guengerich, F Peter; Prough, Russell A

2011-08-15

426

Hemoglobin and red blood cells catalyze atom transfer radical polymerization.  

PubMed

Hemoglobin (Hb) is a promiscuous protein that not only transports oxygen, but also catalyzes several biotransformations. A novel in vitro catalytic activity of Hb is described. Bovine Hb and human erythrocytes were found to display ATRPase activity, i.e., they catalyzed the polymerization of vinyl monomers under conditions typical for atom transfer radical polymerization (ATRP). N-isopropylacrylamide (NIPAAm), poly(ethylene glycol) methyl ether acrylate (PEGA), and poly(ethylene glycol) methyl ether methacrylate (PEGMA) were polymerized using organobromine initiators and the reducing agent ascorbic acid in acidic aqueous solution. In order to avoid chain transfer from polymer radicals to Hb's cysteine residues, the accessible cysteines were blocked by a reaction with a maleimide. The formation of polymers with bromine chain ends, relatively low polydispersity indices (PDI), first order kinetics and an increase in the molecular weight of poly(PEGA) and poly(PEGMA) upon conversion indicate that control of the polymerization by Hb occurred via reversible atom transfer between the protein and the growing polymer chain. For poly(PEGA) and poly(PEGMA), the reactions proceeded with a good to moderate degree of control. Sodium dodecyl sulfate (SDS) gel electrophoresis, circular dichroism spectroscopy, and time-resolved ultraviolet-visible (UV-vis) spectroscopy revealed that the protein was stable during polymerization, and only underwent minor conformational changes. As Hb and erythrocytes are readily available, environmentally friendly, and nontoxic, their ATRPase activity is a useful tool for synthetic polymer chemistry. Moreover, this novel activity enhances the understanding of Hb's redox chemistry in the presence of organobromine compounds. PMID:23739032

Silva, Tilana B; Spulber, Mariana; Kocik, Marzena K; Seidi, Farzad; Charan, Himanshu; Rother, Martin; Sigg, Severin J; Renggli, Kasper; Kali, Gergely; Bruns, Nico

2013-08-12

427

Electrochemical Investigations into Kinase-Catalyzed Transformations of Tau Protein  

PubMed Central

The formation of neurofibrillary tangles by hyperphosphorylated tau is a well-recognized hallmark of Alzheimer’s disease. Resulting from malfunctioning protein kinases, hyperphosphorylated tau is unable to bind microtubules properly, causing it to self-associate and aggregate. The effects of tau phosphorylation on tau conformation and aggregation are still largely unexplored. The conformational analysis of tau and its hyperphosphorylated forms is usually performed by a variety of spectroscopic techniques, all of which require ample sample concentrations and/or volumes. Here we report on the use of surface based electrochemical techniques that allow for detection of conformational changes and orientation of tau protein as a function of tau phosphorylation by tyrosine and serine/threonine kinases. The electrochemical methods utilize 5?-?-ferrocenyl adenosine triphosphate (Fc-ATP) derivative as a cosubstrate and tau immobilized on gold surface to probe the role of the following protein kinases: Sarcoma related kinase (Src), Abelson tyrosine kinase (Abl), tau-tubulin kinase (TTBK), proto-oncogene tyrosine protein kinase Fyn (Fyn), and glycogen synthase kinase 3-? (Gsk-3?). The single kinase and sequential kinase-catalyzed Fc-phosphorylations modulate the electrochemical signal, pointing to the dramatic changes around the Fc group in the Fc-phosphorylated tau films. The location and orientation of the Fc-group in Fc-tau film was investigated by the surface plasmon resonance based on antiferrocene antibodies. Additional surface characterization of the Fc-tau films by time-of-flight secondary ion-mass spectrometry and X-ray photoelectron spectroscopy revealed that Fc-phosphorylations influence the tau orientation and conformation on surfaces. When Fc-phosphorylations were performed in solution, the subsequently immobilized Fc-tau exhibited similar trends. This study illustrates the validity and the utility of the labeled electrochemical approach for probing the changes in protein film properties, conformation, and orientation as a function of the enzymatically catalyzed modifications. PMID:23687953

2013-01-01

428

Highly Enantioselective Syntheses of Functionalized r-Methylene--butyrolactones via Rh(I)-catalyzed Intramolecular Alder Ene  

E-print Network

(I)-catalyzed Intramolecular Alder Ene Reaction: Application to Formal Synthesis of (+)-Pilocarpine Aiwen Lei, Minsheng He -lactones has shown its potential efficiency.7 Extensive studies on transition metal-catalyzed Alder ene a highly enantioselective Rh-catalyzed intramolecular Alder ene reaction for the synthesis

Zhang, Xumu

429

Calreticulin mutations in Chinese with primary myelofibrosis  

PubMed Central

We tested 357 Chinese with primary myelofibrosis for mutations in CALR, JAK2 and MPL. CALR mutations were detected in 76 subjects (21%). There were 24 (32%) type-1 (L367fs*46) and 49 (64%) type-2 (K385fs*47) mutations. Seventy-two of 168 subjects (43%) without a JAK2 or MPL mutation had a CALR mutation. Subjects with a type-2 CALR mutation had lower hemoglobin concentrations (P=0.001), lower WBC counts (P<0.001), a higher percentage of blood blasts (P=0.009), and higher conventional (P<0.001) and Chinese-adjusted Dynamic International Prognostic Scoring System (P<0.001) scores compared with subjects with JAK2 mutations. Subjects with a type-2 CALR mutation were also likely to have abnormal platelet levels (<100 × 109/L, P=0.01 or >450 × 109/L, P=0.042) and no splenomegaly (P=0.004). Type-2 CALR mutation or no detectable mutation was an independent high-risk factor for survival in multivariate analyses. These data suggest the ratio between type-1 and type-2 mutations is reversed in Chinese with primary myelofibrosis compared with populations of subjects with primary myelofibrosis of predominately European descent. The unfavorable prognostic impact of CALR mutations in Chinese with primary myelofibrosis is only seen in those with type-2 mutations. These data underscore the need to evaluate the prognostic impact of genetic mutations in different populations. PMID:24997152

Li, Bing; Xu, Junqing; Wang, Jingya; Gale, Robert Peter; Xu, Zefeng; Cui, Yajuan; Yang, Lin; Xing, Ruixian; Ai, Xiaofei; Qin, Tiejun; Zhang, Yue; Zhang, Peihong; Xiao, Zhijian

2014-01-01

430

Protective role of calreticulin in HFE hemochromatosis  

Microsoft Academic Search

HFE gene mutations are associated with over 80% of cases of hereditary hemochromatosis (HH), an iron-overload disease in which the liver is the most frequently affected organ. Research on HFE has traditionally focused on its interaction with the transferrin receptor. More recent studies have suggested a more complex function for this nonclassical MHC-I protein. The aim of this study was

Jorge P. Pinto; Pedro Ramos; Sérgio F. de Almeida; Susana Oliveira; Laura Breda; Marek Michalak; Graça Porto; Stefano Rivella; Maria de Sousa

2008-01-01

431

Highly enantioselective synthesis of ?-, ?-, and ?-chiral 1-alkanols via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA)-Cu- or Pd-catalyzed cross-coupling.  

PubMed

Despite recent advances of asymmetric synthesis, the preparation of enantiomerically pure (?99% ee) compounds remains a challenge in modern organic chemistry. We report here a strategy for a highly enantioselective (?99% ee) and catalytic synthesis of various ?- and more-remotely chiral alcohols from terminal alkenes via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA reaction)-Cu- or Pd-catalyzed cross-coupling. ZACA-in situ oxidation of tert-butyldimethylsilyl (TBS)-protected ?-alkene-1-ols produced both (R)- and (S)-?,?-dioxyfunctional intermediates (3) in 80-88% ee, which were readily purified to the ?99% ee level by lipase-catalyzed acetylation through exploitation of their high selectivity factors. These ?,?-dioxyfunctional intermediates serve as versatile synthons for the construction of various chiral compounds. Their subsequent Cu-catalyzed cross-coupling with various alkyl (primary, secondary, tertiary, cyclic) Grignard reagents and Pd-catalyzed cross-coupling with aryl and alkenyl halides proceeded smoothly with essentially complete retention of stereochemical configuration to produce a wide variety of ?-, ?-, and ?-chiral 1-alkanols of ?99% ee. The M?NP ester analysis has been applied to the determination of the enantiomeric purities of ?- and ?-chiral primary alkanols, which sheds light on the relatively undeveloped area of determination of enantiomeric purity and/or absolute configuration of remotely chiral primary alcohols. PMID:24912191

Xu, Shiqing; Oda, Akimichi; Kamada, Hirofumi; Negishi, Ei-ichi

2014-06-10

432

Palladium-catalyzed regioselective azidation of allylic C-H bonds under atmospheric pressure of dioxygen.  

PubMed

A palladium-catalyzed allylic azidation of alkenes with sodium azide under atmospheric pressure of dioxygen was developed. This methodology provides a new efficient and simple route for accessing allylic azides. Furthermore, the one-pot process consisting of Pd-catalyzed allylic azidation of alkenes and Cu-catalyzed 1,3-dipolar cycloaddition led directly to the 1,2,3-triazole from the alkene. The formed allylic azide can be also in situ reduced to the allylic amine or oxidized to the alkenyl nitrile. PMID:24733286

Chen, Huoji; Yang, Wanfei; Wu, Wanqing; Jiang, Huanfeng

2014-06-01

433

Highly Efficient Route to Fused Polycyclic Aromatics via Palladium-Catalyzed Aryne Annulation by Aryl Halides  

PubMed Central

Polycyclic aromatic and heteroaromatic hydrocarbons have been synthesized in high yield by two different processes involving the Pd-catalyzed annulation of arynes. The first process involves a Pd-catalyzed annulation of arynes by 2-halobiaryls and related vinylic halides. The second process utilizes a Pd-catalyzed double annulation of arynes by simple aryl halides. Both processes appear to involve the catalytic, stepwise coupling of two very reactive substrates, an aryne and an organopalladium species, to generate excellent yields of cross-coupled products. PMID:17194103

Liu, Zhijian

2008-01-01

434

Rh(I)-Catalyzed Direct Arylation of Pyridines and Quinolines  

SciTech Connect

The pyridine and quinoline nuclei are privileged scaffolds that occupy a central role in many medicinally relevant compounds. Consequently, methods for their expeditious functionalization are of immediate interest. However, despite the immense importance of transition-metal catalyzed cross-coupling for the functionalization of aromatic scaffolds, general solutions for coupling 2-pyridyl organometallics with aryl halides have only recently been presented. Direct arylation at the ortho position of pyridine would constitute an even more efficient approach because it eliminates the need for the stoichiometric preparation and isolation of 2-pyridyl organometallics. Progress towards this goal has been achieved by activation of the pyridine nucleus for arylation via conversion to the corresponding pyridine N-oxide or N-iminopyridinium ylide. However, this approach necessitates two additional steps: activation of the pyridine or quinoline starting material, and then unmasking the arylated product. The use of pyridines directly would clearly represent the ideal situation both in terms of cost and simplicity. We now wish to document our efforts in this vein, culminating in an operationally simple Rh(I)-catalyzed direct arylation of pyridines and quinolines. We recently developed an electron-rich Rh(I) system for catalytic alkylation at the ortho position of pyridines and quinolines with alkenes. Therefore, we initially focused our attention on the use of similarly electron-rich Rh(I) catalysts for the proposed direct arylation. After screening an array of electron-rich phosphine ligands and Rh(I) salts, only marginal yields (<20%) of the desired product were obtained. Much more efficient was an electron-poor Rh(I) system with [RhCl(CO){sub 2}]{sub 2} as precatalyst (Table 1). For the direct arylation of picoline with 3,5-dimethyl-bromobenzene, addition of P(OiPr){sub 3} afforded a promising 40% yield of the cross coupled product 1a (entry 1). The exclusion of phosphite additive proved even more effective, with the yield of 1a improving to 61% (entry 2). Further enhancement in yield was not observed upon the inclusion of other additives such as MgO (entry 3), various organic bases (entries 4, 5), or a protic acid source (entry 6). Absolute concentration proved very important, with the best results being obtained at relatively high concentrations of the aryl bromide (compare entries 7 and 8). A marginal improvement was observed upon running the reaction with 6 equivalents of 2-methyl pyridine (entry 9). The reaction temperature could also be increased to 175 or 190 C while maintaining reaction yield, to enable the reaction time to be reduced to 24 h (entries 10 and 11). In summary, we have developed a Rh(I)-catalyzed strategy for the direct arylation of pyridines and quinolines. The heterocycle is used without the need for prefunctionalization, and all reaction components are inexpensive and readily available. The strategy represents an expeditious route to an important class of bis(hetero)aryls and should be of broad utility.

Berman, Ashley; Lewis, Jared; Bergman, Robert; Ellman, Jonathan

2008-07-29

435

High power density yeast catalyzed microbial fuel cells  

NASA Astrophysics Data System (ADS)

Microbial fuel cells leverage whole cell biocatalysis to convert the energy stored in energy-rich renewable biomolecules such as sugar, directly to electrical energy at high efficiencies. Advantages of the process include ambient temperature operation, operation in natural streams such as wastewater without the need to clean electrodes, minimal balance-of-plant requirements compared to conventional fuel cells, and environmentally friendly operation. These make the technology very attractive as portable power sources and waste-to-energy converters. The principal problem facing the technology is the low power densities compared to other conventional portable power sources such as batteries and traditional fuel cells. In this work we examined the yeast catalyzed microbial fuel cell and developed methods to increase the power density from such fuel cells. A combination of cyclic voltammetry and optical absorption measurements were used to establish significant adsorption of electron mediators by the microbes. Mediator adsorption was demonstrated to be an important limitation in achieving high power densities in yeast-catalyzed microbial fuel cells. Specifically, the power densities are low for the length of time mediator adsorption continues to occur. Once the mediator adsorption stops, the power densities increase. Rotating disk chronoamperometry was used to extract reaction rate information, and a simple kinetic expression was developed for the current observed in the anodic half-cell. Since the rate expression showed that the current was directly related to microbe concentration close to the electrode, methods to increase cell mass attached to the anode was investigated. Electrically biased electrodes were demonstrated to develop biofilm-like layers of the Baker's yeast with a high concentration of cells directly connected to the electrode. The increased cell mass did increase the power density 2 times compared to a non biofilm fuel cell, but the power density increase was shown to quickly saturate with cell mass attached on the electrode. Based on recent modelling data that suggested that the electrode currents might be limited by the poor electrical conductivity of the anode, the power density versus electrical conductivity of a yeast-immobilized anode was investigated. Introduction of high aspect ratio carbon fiber filaments to the immobilization matrix increased the electrical conductivity of the anode. Although a higher electrical conductivity clearly led to an increase in power densities, it was shown that the principal limitation to power density increase was coming from proton transfer limitations in the immobilized anode. Partial overcoming of the gradients lead a power density of ca. 250 microW cm-2, which is the highest reported for yeast powered MFCs. A yeast-catalyzed microbial fuel cell was investigated as a power source for low power sensors using raw tree sap. It was shown that yeast can efficiently utilize the sucrose present in the raw tree sap to produce electricity when excess salt is added to the medium. Therefore the salinity of a potential energy source is an important consideration when MFCs are being considered for energy harvesting from natural sources.

Ganguli, Rahul

436

Flame Synthesis Used to Create Metal-Catalyzed Carbon Nanotubes  

NASA Technical Reports Server (NTRS)

Metal-catalyzed carbon nanotubes are highly ordered carbon structures of nanoscale dimensions. They may be thought of as hollow cylinders whose walls are formed by single atomic layers of graphite. Such cylinders may be composed of many nested, concentric atomic layers of carbon or only a single layer, the latter forming a single-walled carbon nanotube. This article reports unique results using a flame for their synthesis. Only recently were carbon nanotubes discovered within an arc discharge and recognized as fullerene derivatives. Today metal-catalyzed carbon nanotubes are of great interest for many reasons. They can be used as supports for the metal catalysts like those found in catalytic converters. Open-ended nanotubes are highly desirable because they can be filled by other elements, metals or gases, for battery and fuel cell applications. Because of their highly crystalline structure, they are significantly stronger than the commercial carbon fibers that are currently available (10 times as strong as steel but possessing one-sixth of the weight). This property makes them highly desirable for strengthening polymer and ceramic composite materials. Current methods of synthesizing carbon nanotubes include thermal pyrolysis of organometallics, laser ablation of metal targets within hydrocarbon atmospheres at high temperatures, and arc discharges. Each of these methods is costly, and it is unclear if they can be scaled for the commercial synthesis of carbon nanotubes. In contrast, flame synthesis is an economical means of bulk synthesis of a variety of aerosol materials such as carbon black. Flame synthesis of carbon nanotubes could potentially realize an economy of scale that would enable their use in common structural materials such as car-body panels. The top figure is a transmission electron micrograph of a multiwalled carbon nanotube. The image shows a cross section of the atomic structure of the nanotube. The dark lines are individual atomic layer planes of carbon, seen here in cross section. They form a nested series of concentric cylinders, much like the growth rings on a tree. This sample was obtained by the supported catalyst method, whereby the nanoscale catalysts are dispersed on a substrate providing their support. The substrate with catalyst particles was immersed within an acetylene diffusion flame to which nitrogen had been added to eliminate soot formation. Upon removal from the flame, the nanotubes were dispersed on a holder suitable for electron microscopy. Although not seen in the figure, the tube diameter reflects that of the catalyst particle.

VanderWal, Randy L.

2001-01-01

437

Lipase catalyzed esterification of glycidol in organic solvents  

SciTech Connect

The authors studied the resolution of racemic glycidol through esterification with butyric acid catalyzed by porcine pancreatic lipase in organic media. A screening of seven solvents (log P values between 0.49 and 3.0, P being the n-octanol-water partition coefficient of the solvent) showed that neither log P nor the logarithm of the molar solubility of water in the solvent provides good correlations between enantioselectivity and the properties of the organic media. Chloroform was one of the best solvents as regards the enantiometic purity (e.p.) of the ester produced. In this solvent, the optimum temperature for the reaction was determined to be 35C. The enzyme exhibited maximum activity at a water content of 13 [plus minus] 2% (w/w). The enantiomeric purity obtained was 83 [plus minus] 2% of (S)-glycidol butyrate and did not depend on the alcohol concentration or the enzyme water content for values of these parameters up to 200 mM and 25% (w/w), respectively. The reaction was found to follow a BiBi mechanism.

Martins, J.F.; Nunes da Ponte, M.; Barreiros, S. (Univ. Nova de Lisboa, Oeiras (Portugal). Centro de Tecnologia Quimica e Biologica)

1993-08-05

438

Electrophoresis-chemiluminescence detection of phenols catalyzed by hemin.  

PubMed

Based on the catalytic activity of hemin, an efficient biocatalyst, an indirect capillary electrophoresis-chemiluminescence (CE-CL) detection method for phenols using a hemin-luminol-hydrogen peroxide system was developed. Through a series of static injection experiments, hemin was found to perform best in a neutral solution rather than an acidic or alkaline medium. Although halide ions such as Br(-) and F(-) could further enhance the CL signal catalyzed by hemin, it is difficult to apply these conditions to this CE-CL detection system because of the self-polymerization of hemin, as it hinders the CE process. The addition of concentrated ammonium hydroxide to an aqueous/dimethyl sulfoxide solution of hemin-luminol afforded a stable CE-CL baseline. The indirect CE-CL detection of five phenols using this method gave the following limits of detections: 4.8 × 10(-8) mol/L (o-sec-butylphenol), 4.9 × 10(-8) mol/L (o-cresol), 5.4 × 10(-8) mol/L (m-cresol), 5.3 × 10(-8) mol/L (2,4-dichlorophenol) and 7.1 × 10(-8) mol/L (phenol). PMID:24115262

Shu, Lu; Zhu, Jinkun; Wang, Qingjiang; He, Pingang; Fang, Yuzhi

2014-09-01

439

Dephenolization of industrial wastewaters catalyzed by polyphenol oxidase  

SciTech Connect

A new enzymatic method for the removal of phenols from industrial aqueous effluents has been developed. The method uses the enzyme polyphenol oxidase which oxidizes phenols to the corresponding o-quinones; the latter then undergo a nonenzymatic polymerization to form water-insoluble aggregates. Therefore, the enzyme in effect precipitates phenols from water. Polyphenol oxidase has been found to nearly completely dephenolize solutions of phenol in the concentration range from 0.01 to 1.0 g/L. The enzymatic treatment is effective over a wide range of pH and temperature; a crude preparation of polyphenol oxidase (mushroom extract) is as effective as a purified, commercially obtained version. In addition to phenol itself, polyphenol oxidase is capable of precipitating from water a number of substituted phenols (cresols, chlorophenols, naphthol, etc.). Also, even pollutants which are unreactive towards polyphenol oxidase can be enzymatically coprecipitated with phenol. The polyphenol oxidase treatment has been successfully used to dephenolize two different real industrial wastewater samples, from a plant producing triarylphosphates and from a coke plant. The advantage of the polyphenol oxidase dephenolization over the peroxidase-catalyzed one previously elaborated by the authors is that the former enzyme uses molecular oxygen instead of costly hydrogen peroxide (used by peroxidase) as an oxidant.

Atlow, S.C.; Bonadonna-Aparo, L.; Klibanov, A.M.

1984-01-01

440

Heterogeneous catalyzed benzylic acetoxylation of methylated aromatic hydrocarbons  

SciTech Connect

The palladium-catalyzed acetoxylation of toluene to benzyl acetate is highly dependent on particle size. The rate of reaction is highest with 30--35 [Angstrom] particles corresponding to a 0.33 dispersion. Catalysts prepared and reduced by controlled methods before being contacted with the reaction medium, ex situ catalysts, were found to yield lower reaction rates than catalysts prepared in the reaction medium, in situ. Potassium ion-encapsulation in palladium during in situ preparation is a possible explanation for this result. Tin is required to reduce Pd[sup 2+] to Pd[sup 0] in the in situ system, but is not required for the ex situ catalyst. The improvement in activity of the ex situ catalyst in the presence of tin may be due to the reducibility of Sn[sup 4+] to Sn[sup 2+] during oxygen-poor regimes. Results obtained with diverse methylated aromatic hydrocarbons indicate that the aromatic ring interactions with the palladium surface via [pi]-donation before oxidation occurs. 37 refs., 7 figs., 5 tabs.

Benazzi, E.; Mimoun, H.; Cameron, C.J. (Institut Francais du Petrole, Rueil-Malmaison (France))

1993-04-01

441

Primordial lithium abundance in catalyzed big bang nucleosynthesis  

SciTech Connect

There exists a well-known problem with the {sup 7}Li+{sup 7}Be abundance predicted by standard big bang nucleosynthesis being larger than the value observed in population II stars. The catalysis of big bang nucleosynthesis by metastable, {tau}{sub X} > or approx. 10{sup 3} sec, charged particles X{sup -} is capable of suppressing the primordial {sup 7}Li+{sup 7}Be abundance and making it consistent with the observations. We show that to produce the correct abundance, this mechanism of suppression places a requirement on the initial abundance of X{sup -} at temperatures of 4x10{sup 8} K to be on the order of or larger than 0.02 per baryon, which is within the natural range of abundances in models with metastable electroweak-scale particles. The suppression of {sup 7}Li+{sup 7}Be is triggered by the formation of ({sup 7}BeX{sup -}) compound nuclei, with fast depletion of their abundances by catalyzed proton reactions, and in some models by direct capture of X{sup -} on {sup 7}Be. The combination of {sup 7}Li+{sup 7}Be and {sup 6}Li constraints favors the window of lifetimes, 1000 s < or approx. {tau}{sub X}{<=}2000 s.

Bird, Chris [Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8P 1A1 (Canada); Koopmans, Kristen [Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2J 2W9 (Canada); Pospelov, Maxim [Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8P 1A1 (Canada); Perimeter Institute for Theoretical Physics, Waterloo, Ontario N2J 2W9 (Canada)

2008-10-15

442

Primordial Lithium Abundance in Catalyzed Big Bang Nucleosynthesis  

E-print Network

There exists a well known problem with the Li7+Be7 abundance predicted by standard big bang nucleosynthesis being larger than the value observed in population II stars. The catalysis of big bang nucleosynthesis by metastable, \\tau_X \\ge 10^3 sec, charged particles X^- is capable of suppressing the primordial Li7+Be7, abundance and making it consistent with the observations. We show that to produce the correct abundance, this mechanism of suppression places a requirement on the initial abundance of X^- at temperatures of 4\\times 10^8 K to be on the order of or larger than 0.02 per baryon, which is within the natural range of abundances in models with metastable electroweak-scale particles. The suppression of Li7+Be7, is triggered by the formation of (Be7X^-), compound nuclei, with fast depletion of their abundances by catalyzed proton reactions, and in some models by direct capture of X^- on Be7. The combination of Li7+Be7 and Li6 constraints favours the window of lifetimes, 1000s \\la tau_X \\leq 2000 s.

Chris Bird; Kristen Koopmans; Maxim Pospelov

2007-03-08

443

Feasibility of an antiproton catalyzed fission fragment rocket  

SciTech Connect

The purpose of this project was to investigate the feasibility of an antiproton catalyzed fission fragment rocket (FFR). The FFR is characterized by the extraction of fission fragments from the fissile fuel, and the utilization of their kinetic energy for thrust generation. A significant drawback to previous FFR designs was the requirement to maintain a critical nuclear pile as the fission fragment source. The author examined the possibility of replacing the critical pile with a sub-critical pile driven by antiprotons. Recent experiments have revealed that antiprotons stimulate highly energetic fissions in {sup 238}U, with a neutron multiplicity of 13.7 neutrons per fission. This interaction was used as a throttled neutron source. The pile consisted of layers of fissile coated fibers which are designed to allow fission fragments to escape them, where the fragments collide with a fluid. The heated fluid is then ejected from the rocket to provide thrust. The calculations performed indicate that each antiproton injected into the pile can stimulate 8 or more fissions while maintaining a neutron multiplication of less than 0.4. Based on the results seen, the engine design presented is inadequate. Limitations introduced by the reaction fluid far outweigh the simplicity-of-design gained. Despite this, the basic idea of using the antiproton-U interaction as a source of spacecraft propulsion warrants further study.

Hdinger, D.S.

1992-03-01

444

Remote catalyzation for direct formation of graphene layers on oxides.  

PubMed

Direct deposition of high-quality graphene layers on insulating substrates such as SiO(2) paves the way toward the development of graphene-based high-speed electronics. Here, we describe a novel growth technique that enables the direct deposition of graphene layers on SiO(2) with crystalline quality potentially comparable to graphene grown on Cu foils using chemical vapor deposition (CVD). Rather than using Cu foils as substrates, our approach uses them to provide subliming Cu atoms in the CVD process. The prime feature of the proposed technique is remote catalyzation using floating Cu and H atoms for the decomposition of hydrocarbons. This allows for the direct graphitization of carbon radicals on oxide surfaces, forming isolated low-defect graphene layers without the need for postgrowth etching or evaporation of the metal catalyst. The defect density of the resulting graphene layers can be significantly reduced by tuning growth parameters such as the gas ratios, Cu surface areas, and substrate-to-Cu distance. Under optimized conditions, graphene layers with nondiscernible Raman D peaks can be obtained when predeposited graphite flakes are used as seeds for extended growth. PMID:22332771

Teng, Po-Yuan; Lu, Chun-Chieh; Akiyama-Hasegawa, Kotone; Lin, Yung-Chang; Yeh, Chao-Hui; Suenaga, Kazu; Chiu, Po-Wen

2012-03-14

445

Lysozyme catalyzes the formation of antimicrobial silver nanoparticles.  

PubMed

Hen egg white lysozyme acted as the sole reducing agent and catalyzed the formation of silver nanoparticles in the presence of light. Stable silver colloids formed after mixing lysozyme and silver acetate in methanol and the resulting nanoparticles were concentrated and transferred to aqueous solution without any significant changes in physical properties. Activity and antimicrobial assays demonstrated lysozyme-silver nanoparticles retained the hydrolase function of the enzyme and were effective in inhibiting growth of Escherichia coli, Staphylococcus aureus, Bacillus anthracis, and Candida albicans. Remarkably, lysozyme-silver nanoparticles demonstrated a strong antimicrobial effect against silver-resistant Proteus mirabilis strains and a recombinant E. coli strain containing the multiple antibiotic- and silver-resistant plasmid, pMG101. Results of toxicological studies using human epidermal keratinocytes revealed that lysozyme-silver nanoparticles are nontoxic at concentrations sufficient to inhibit microbial growth. Overall, the ability of lysozyme to assemble silver nanoparticles in a one-step reaction offers a simple and environmentally friendly approach to form stable colloids of nontoxic silver nanoparticles that combine the antimicrobial properties of lysozyme and silver. The results expand the functionality of nanomaterials for biological systems and represent a novel antimicrobial composite for potential aseptics and therapeutic use in the future. PMID:19344124

Eby, D Matthew; Schaeublin, Nicole M; Farrington, Karen E; Hussain, Saber M; Johnson, Glenn R

2009-04-28

446

The role of microemulsions in lipase-catalyzed hydrolysis reactions.  

PubMed

The kinetics of the p-nitrophenyl butyrate hydrolysis reaction, catalyzed by Candida rugosa lipase in the water-in-oil microemulsion cetyltrimethylammonium bromide/water/pentanol/hexane, was investigated. The results described in the present manuscript reveal two peculiar characteristics of the reaction: (i) the initial rate of hydrolysis is very fast and (ii) by decreasing the water content of the microemulsion, the reaction rate approaches the typical behavior of reactions performed in aqueous solution. In particular, for microemulsion systems with a high water content, the end points of the reactions are dictated by the shape stability of the microemulsion. For these systems, our methodological approach shows that the process follows a second-order kinetics equation, indicative of the dual role played by water, which is involved both as a component of the microemulsion, i.e., relevant for the microemulsion stability and as a reagent of the hydrolysis reaction. In contrast, for microemulsions containing a small amount of water, after the hydrolysis reaction the system seems to fall in the no existence range of the microemulsion. Accordingly, the kinetics results are more complex: in the initial stage, the reaction follows a zero-order kinetics equation, while for longer reaction times a first-order kinetics equation fits the experimental data, as would be expected for an enzymatic reaction in a homogeneous system. PMID:24585724

Lopez, Francesco; Cinelli, Giuseppe; Colella, Matilde; De Leonardis, Antonella; Palazzo, Gerardo; Ambrosone, Luigi

2014-01-01

447

Coalification by clay-catalyzed oligomerization of plant monomers. [Methylisoeugenol  

SciTech Connect

During this reporting period, we have obtained a model of montmorillonite clay, and this model has been of great assistance in visualizing how the chemistry of substrate molecules might be altered as it occurs on the surface of the clay. A stereochemical representation of this montmorillonite model is shown. In our previous report, we indicated that the dimerization of methylisoeugenol with the montmorillonite clay K-10 afforded a variety of indanes and indenes which were formed via acid-catalyzed processes. In addition, we have now observed a pair of naphthalene isomers. This observation lends strong support to the hypothesis that radical cation Diels-Alder dimerizations occur on the surface of the montmorillonite clay K-10. Furthermore, when the dimerization is conducted in homogeneous media, only two indanes are formed. However, when this same dimerization is conducted on the surface of K-10, six indanes are produced. Based upon these considerations, the distribution of indane isomers might indicate that dimerization is taking place both in the homogeneous medium surrounding the clay and on the surface of the clay. Samples of K-10 were pretreated with DBU, dicyclohexylamine, triphenylamine, and triton-B. The pretreatments completely inhibited indane formation. In addition, the partially neutralization of K-10 by the pretreatment with finely ground Na{sub 2}CO{sub 3} was attempted. This procedure did not alter the ratios of indanes products from those observed with the untreated K-10.

Orchin, M.; Wilson, R.M.

1989-01-01

448

Stereochemical course of enzyme-catalyzed aminopropyl transfer: spermidine synthase  

SciTech Connect

The R and S enantionmers of S-adenosyl-3-(/sup 2/H)3-(methylthio)-1-propylamine (decarboxylated S-adenosylmethionine), previously synthesized in this laboratory, were incubated with (1,4-/sup 2/H/sub 4/)-putrescine in the presence of spermidine synthase from E. coli. The resulting chiral (/sup 2/H/sub 5/)spermidines were isolated and converted to their N/sub 1/,N/sub 7/-dibocspermidine-N/sub 4/-(1S,4R)-camphanamides. The derivatives were analyzed by 500 MHz /sup 1/H-NMR and the configuration of the chiral center assigned by correlation with the spectra of synthetic chiral (/sup 2/H/sub 3/)dibocspermidine camphanamide standards. The enzyme-catalyzed aminopropyl transfer was shown to occur with net retention of configuration, indicative of a double-displacement mechanism. This result concurs with that of a previous steady-state kinetics study of spermidine synthase isolated from E. coli, but contradicts the single-displacement mechanism suggested by a stereochemical analysis of chiral spermidines biosynthesized in E. coli treated with chirally deuterated methionines. It also indicates that this aminopropyltransferase is mechanistically distinct from the methyltransferases, which have been shown to act via a single-displacement mechanism (net inversion at -CH/sub 3/) in all cases studied to date.

Kullberg, D.W.; Orr, G.R.; Coward, J.K.

1986-05-01

449

Reaction dynamics of ATP hydrolysis catalyzed by P-glycoprotein.  

PubMed

P-glycoprotein (P-gp) is a member of the ABC transporter family that confers drug resistance to many tumors by catalyzing their efflux, and it is a major component of drug-drug interactions. P-gp couples drug efflux with ATP hydrolysis by coordinating conformational changes in the drug binding sites with the hydrolysis of ATP and release of ADP. To understand the relative rates of the chemical step for hydrolysis and the conformational changes that follow it, we exploited isotope exchange methods to determine the extent to which the ATP hydrolysis step is reversible. With ?(18)O4-labeled ATP, no positional isotope exchange is detectable at the bridging ?-phosphorus-O-?-phosphorus bond. Furthermore, the phosphate derived from hydrolysis includes a constant ratio of three (18)O/two (18)O/one (18)O that reflects the isotopic composition of the starting ATP in multiple experiments. Thus, H2O-exchange with HPO4(2-) (Pi) was negligible, suggesting that a [P-gp·ADP·Pi] is not long-lived. This further demonstrates that the hydrolysis is essentially irreversible in the active site. These mechanistic details of ATP hydrolysis are consistent with a very fast conformational change immediately following, or concomitant with, hydrolysis of the ?-phosphate linkage that ensures a high commitment to catalysis in both drug-free and drug-bound states. PMID:24506763

Scian, Michele; Acchione, Mauro; Li, Mavis; Atkins, William M

2014-02-18

450

Pheromone deactivation catalyzed by receptor molecules: a quantitative kinetic model.  

PubMed

A quantitative model of pheromone-receptor interaction and pheromone deactivation, the supposed rate-limiting processes underlying the receptor potential kinetics, is worked out for the moth Antheraea polyphemus. In this model, the pheromone interacts with the receptor molecule while bound to the reduced form of the pheromone binding protein. The receptor molecules--besides their receptor function--catalyze the observed shift of the pheromone-binding protein from the reduced to the oxidized form (Ziegelberger, G., Eur. J. Biochem., 232, 706-711, 1995), which deactivates the pheromone bound to pheromone binding protein. With the following parameters, the model fits morphological, radiometric, electrophysiological and biochemical data: a maximum estimate of 1.7 x 10(7) receptor molecules/cell (with 40,000 units/micron 2 of receptor cell membrane), rate constants k1 = 0.2/(s.microM) for the association, k2 = 10/s for the dissociation of the ternary complex of binding protein, pheromone and receptor, and k3 = 10/s for the deactivation via the redox shift. With these parameters, the duration of elementary receptor potentials elicited by single pheromone molecules (approximately 50 ms) reflects the lifetime of the ternary complex, tau = 1/(k2 + k3). The receptor occupancy produced by the model for threshold stimuli fits the sensitivity of the receptor cell to single pheromone molecules. PMID:9759524

Kaissling, K E

1998-08-01

451

Molecular mechanisms of cobalt-catalyzed hydrogen evolution  

PubMed Central

Several cobalt complexes catalyze the evolution of hydrogen from acidic solutions, both homogeneously and at electrodes. The detailed molecular mechanisms of these transformations remain unresolved, largely owing to the fact that key reactive intermediates have eluded detection. One method of stabilizing reactive intermediates involves minimizing the overall reaction free-energy change. Here, we report a new cobalt(I) complex that reacts with tosylic acid to evolve hydrogen with a driving force of just 30 meV/Co. Protonation of CoI produces a transient CoIII-H complex that was characterized by nuclear magnetic resonance spectroscopy. The CoIII-H intermediate decays by second-order kinetics with an inverse dependence on acid concentration. Analysis of the kinetics suggests that CoIII-H produces hydrogen by two competing pathways: a slower homolytic route involving two CoIII-H species and a dominant heterolytic channel in which a highly reactive CoII-H transient is generated by CoI reduction of CoIII-H. PMID:22949704

Marinescu, Smaranda C.; Winkler, Jay R.; Gray, Harry B.

2012-01-01

452

Phase-transfer-catalyzed asymmetric synthesis of axially chiral anilides.  

PubMed

Catalytic asymmetric synthesis of axially chiral o-iodoanilides and o-tert-butylanilides as useful chiral building blocks was achieved by means of binaphthyl-modified chiral quaternary ammonium-salt-catalyzed N-alkylations under phase-transfer conditions. The synthetic utility of axially chiral products was demonstrated in various transformations. For example, axially chiral N-allyl-o-iodoanilide was transformed to 3-methylindoline by means of radical cyclization with high chirality transfer from axial chirality to C-centered chirality. Furthermore, stereochemical information on axial chirality in o-tert-butylanilides could be used as a template to control the stereochemistry of subsequent transformations. The transition-state structure of the present phase-transfer reaction was discussed on the basis of the X-ray crystal structure of ammonium anilide, which was prepared from binaphthyl-modified chiral ammonium bromide and o-iodoanilide. The chiral tetraalkylammonium bromide as a phase-transfer catalyst recognized the steric difference between the ortho substituents on anilide to obtain high enantioselectivity. The size and structural effects of the ortho substituents on anilide were investigated, and a wide variety of axially chiral anilides that possess various functional groups could be synthesized with high enantioselectivities. This method is the only general way to access a variety of axially chiral anilides in a highly enantioselective fashion reported to date. PMID:24273122

Liu, Kun; Wu, Xiangfei; Kan, S B Jennifer; Shirakawa, Seiji; Maruoka, Keiji

2013-12-01

453

Muon Catalyzed Fusion in 3 K Solid Deuterium  

E-print Network

Muon catalyzed fusion in deuterium has traditionally been studied in gaseous and liquid targets. The TRIUMF solid-hydrogen-layer target system has been used to study the fusion reaction rates in the solid phase of D_2 at a target temperature of 3 K. Products of two distinct branches of the reaction were observed; neutrons by a liquid organic scintillator, and protons by a silicon detector located inside the target system. The effective molecular formation rate from the upper hyperfine state of $\\mu d$ and the hyperfine transition rate have been measured: $\\tilde{\\lambda}_(3/2)=2.71(7)_{stat.}(32)_{syst.} \\mu/s$, and $\\tilde{\\lambda}_{(3/2)(1/2)} =34.