Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.4.99.6 (sialyltransferase)
1,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Human chorionic gonadotrophin (hCG) is a heterodimeric glycoprotein hormone consisting of an alpha- and a beta-subunit, both containing two N-linked, complex-type glycans. Using this hormone as a model glycoprotein, the influence of its polypeptide part on the activity and specificity of bovine colostrum CMP-NeuAc:Gal beta 1----4GlcNAc-R alpha 2----6-sialyltransferase (alpha 6-sialyltransferase) was investigated. Initial rates of sialic acid incorporation into the desialylated glycans of hCG alpha and hCG beta in the heterodimer were higher with the alpha-subunit. This appeared to be due to a higher V which, together with a slightly lowered affinity (higher Km), resulted in a higher kinetic efficiency of the sialyltransferase for the glycans of this subunit. By contrast, the kinetic parameters did not differ significantly when the subunits were in the free form, indicating that the differences in the kinetics of sialylation found for the subunits in the heterodimeric state were not caused by the differences in N-linked carbohydrate structures of the subunits. It is proposed that these effects are due to conformational constraints which the polypeptide moieties put on the glycan chains upon dimerization. Furthermore, it was investigated whether the polypeptide of hCG would interfere with the sialyltransferase so as to alter the branch specificity of the enzyme. 1H-NMR spectroscopy (400 MHz) of the glycan chains, alpha 6-sialylated in vitro, showed that the enzyme highly prefers the galactosyl residue at the Gal beta 1----4GlcNAc beta 1----2-Man alpha 1----3Man branch for attachment of the first mol of sialic acid into the diantennary glycans of desialylated hCG.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The polypeptide part of human chorionic gonadotrophin affects the kinetics of alpha 6-sialylation of its N-linked glycans but does not alter the branch specificity of CMP-NeuAc:Gal beta 1----4GlcNAc-R alpha 2----6-sialyltransferase. 160 56

Previous studies have shown that purified mitochondrial outer membrane is able to catalyze the transfer of sialic acid from CMP-Neu5Ac to an exogenous asialoglycoprotein acceptor, asialofetuin. Considering the heterogeneity of the glycan chains borne by this glycoprotein, an investigation of mitochondrial sialyltransferase activities was undertaken. Our data provide evidence for the existence of two distinct sialyltransferases in purified mitochondrial outer membranes. The use of different acceptor substrates, the temperature dependence of these enzymes, and their different sensitivity towards a sulfhydryl reagent, p-CMB, allowed us to discriminate between a galactoside alpha(2-3) sialyltransferase and a galactoside alpha(2-6) sialyltransferase presumably involved in the sialylation of O- and N-glycan chains of glycoprotein, respectively. These results are discussed in terms of mitochondrial autonomy for post-translational events.
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PMID:Sialylation processes in mitochondria: evidence for two distinct sialyltransferases located in the outer membrane. 172 30

The CA 125 antigenic determinant has been shown to be elevated in the serum of ovarian cancer patients and is a useful prognostic marker. The chemical epitope which characterizes the CA 125 antigen is found on a high molecular weight glycoprotein and has been suggested to be carbohydrate in nature. This study was undertaken to establish the relationship of a carbohydrate to the epitope recognized by the monoclonal antibody, OC 125. Along this line a carbohydrate structure conjugated to bovine serum albumin (BSA), was enzymatically sialylated using a purified sialyltransferase to yield NeuAcGal[GlcNAc]GalNAc-OC6H4N = N-BSA. This sialylated product was used to immunize a goat and two rabbits for the development of polyclonal antisera. The resultant antisera were tested against related carbohydrates in EIA biased competitive inhibition assays. It was determined that the GlcNAc(beta 1-6)GalNAc residue was immunologically dominant for all antisera tested. As the immune response matured (greater than 40 days), there was an increase in the proportion of the antibodies that were directed to the NeuAc(alpha 2-3)Gal(beta 1-3)GalNAc residue compared to the nonsialylated form. Known CA 125 molecules did not inhibit the binding of raised antisera to the sialylated product, nor did the sialylated product react with OC 125 monoclonal antibodies. It was therefore concluded that the carbohydrate structure in question is not the epitope, or is not a large enough part of the epitope to be recognized in these assays by the OC 125 monoclonal antibodies.
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PMID:Antigenic studies on an enzymatically sialylated carbohydrate: NeuAc(alpha 2-3)Gal(beta 1-3)[GlcNAc(beta 1-6)]GalNAc. 205 2

CMP-N-acetylneuraminic acid: glycoprotein sialyltransferase activities were assayed in microsomal fractions from chicken liver and hepatoma, induced by the leukosis virus strain Mc-29, using asialofetuin as the substrate acceptor of N-acetylneuraminic acid. The effect of some nucleotides and metal ions on the enzyme activity was investigated. Kinetic studies revealed that the Km values toward asialofetuin at a saturation concentrations of CMP-N-acetylneuraminic acid for both liver and hepatoma enzymes are very closed, while V value was lower for the tumor enzyme. The liver and hepatoma enzymes have no exogenous Mn cations requirement and are inhibited by CTP, CMP and ATP. CMP was shown to act as a competitive inhibitor with an apparent Ki of 0.24 mM for the liver and 0.16 mM for hepatoma enzyme, respectively.
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PMID:Partial characterization of microsomal sialyltransferase from chicken liver and hepatoma Mc-29: I. Effect of nucleotides and metal ions. 208 38

Microsomal sialyltransferase was assayed in chicken liver and hepatoma Mc-29 utilizing liver and hepatoma microsomal glycoprotein fractions, treated with Triton X-100, as exogenous acceptors. In a homologous assay system containing enzyme and acceptor from one and the same tissue no quantitative dependence of enzyme activity was revealed with increasing amount of the acceptor. In mixed experiments in which liver enzyme activity was tested towards hepatoma acceptor glycoproteins, a gradual drop in sialyltransferase activity occurred with increasing quantities of the acceptor. This effect seems to be a consequence of the presence of some inhibitor in the microsomal fractions from the hepatoma cells.
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PMID:Partial characterization of microsomal sialyltransferase from chicken liver and hepatoma Mc-29: II. Measurement of enzyme activities utilizing microsomal glycoproteins as exogenous acceptors. 208 39

This paper presents a very sensitive fluorometric assay for sialyltransferase activity based on the transfer of 5-acetamido-9-deoxy-9-fluoresceinylthioure-idoneuraminic acid onto distinct glycoproteins, thus allowing determination of acceptor specificities. Acceptor protein-bound fluorescence was quantified after gel filtration which separated fluorescent sialoglycoprotein from the fluorescence-labeled CMP-glycoside donor. Kinetic constants obtained for five different purified sialyltransferases indicated that CMP-9-fluoresceinyl-NeuAc was a suitable donor substrate for each enzyme, affording low Km values and Vmax values comparable in magnitude (15-100%) to that obtained with the parent CMP-NeuAc. Sensitivity was enhanced 200- to 1000-fold compared to the radiometric sialyltransferase assay as it is used routinely. The method was applied to determination of the kinetic properties of purified rat liver alpha 2,6-sialyltransferase with four separate glycoprotein acceptors differing in glycan structure, employing very small amounts of donor, acceptor, and enzyme, and to the study of sialyltransferase activity of the human promyelocytic cell line HL-60 toward three different acceptors.
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PMID:A highly sensitive fluorometric assay for sialyltransferase activity using CMP-9-fluoresceinyl-NeuAc as donor. 219 78

Little is currently known about the mechanisms by which the cellular glycosylation machinery is regulated to produce cell type-specific glycosylation sequences on glycoprotein and glycolipid sugar chains. Previously, we have shown that one enzyme involved in terminal glycosylation, beta-galactoside alpha 2,6-sialyltransferase, is expressed in a tissue-specific fashion, with the highest enzyme activity as well as mRNA levels being found in the liver. In addition, the liver mRNA was found to be 4.3 kilobases (kb) in size as compared to a larger message of 4.7 kb in other tissues. To understand the cellular regulation of expression of this sialyltransferase, we have cloned the rat gene encoding the 4.3-kb liver mRNA and found that it spans 40 kb of genomic DNA and contains 6 exons. The gene was found to be very similar in size and exon organization to the murine beta 1,4-galactosyltransferase gene, even though this enzyme has no sequence homology to alpha 2,6-sialyltransferase. The promoter responsible for the production of the liver alpha 2,6-sialyltransferase mRNA is approximately 50-fold more active in a hepatoma cell line known to express this enzyme (HepG2) than in a cell line shown not to express this enzyme (Chinese hamster ovary) and contains consensus binding sites for the liver restricted transcription factors HNF-1 and DBP as well as the transcription factors AP-1 and AP-2. These observations are in accord with the restricted expression of the 4.3-kb mRNA, and provides evidence for the cellular regulation of glycosylation at the level of transcription.
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PMID:Organization of the beta-galactoside alpha 2,6-sialyltransferase gene. Evidence for the transcriptional regulation of terminal glycosylation. 224 92

We have examined the role of CMP-NeuAc:Gal beta 1-3GalNAc-R alpha(2-3)-sialyltransferase in fresh leukemia cells and leukemia-derived cell lines. Enzyme activity in normal granulocytes using Gal beta 1-3GalNAc alpha-o-nitrophenyl as substrate was 1.5 +/- 0.7 nmol/mg/h whereas activity in morphologically mature granulocytes from 6 patients with chronic myelogenous leukemia (CML) was 4.2 +/- 1.6 nmol/mg/h (P less than 0.05). Myeloblasts from 5 patients with CML in blast crisis showed enzyme activity levels of 6.5 +/- 2.5 nmol/mg/h. From 2 patients with CML, both blasts and granulocytes were obtained, with higher enzyme activity in the patients' blasts (7.1 nmol/mg/h) than in their granulocytes (4.9 nmol/mg/h) in both cases, suggesting that the increase in enzyme activity is related to the differentiation or proliferation status of the CML cells. However, similarly high enzyme levels were also seen in myeloblasts from acute myeloblastic leukemia patients (5.6 +/- 1.4 nmol/mg/h) and in some acute myeloblastic leukemia-derived cell lines (KG1a and HL60), suggesting that increased levels of this enzyme are not directly correlated with the presence of the Ph1 chromosome. This alpha(2-3)-sialyltransferase activity can also be detected in normal peripheral blood lymphocytes and exhibits increased activity in chronic lymphocytic leukemia cells and acute lymphoblastic leukemia. These data suggest that the level of enzyme activity may vary with growth rate and maturation status in myeloid and lymphoid hemopoietic cells. Finally, we have identified a glycoprotein in acute myeloblastic leukemia cells that serves as a substrate for the alpha(2-3)-sialyltransferase. The desialylated form of the glycoprotein was resialylated in vitro by the purified placental form of this alpha(2-3)-sialyltransferase and exhibits a molecular weight of about 150,000.
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PMID:Human leukemic myeloblasts and myeloblastoid cells contain the enzyme cytidine 5'-monophosphate-N-acetylneuraminic acid:Gal beta 1-3GalNAc alpha (2-3)-sialyltransferase. 237 65

Granulocytes from patients with chronic myelogenous leukemia (CML) are morphologically identical to their normal counterparts but show marked differences in circulation patterns and in some membrane properties. We have previously shown that there is abnormal lectin binding to CML granulocytes, and aberrant sialylation of membrane glycoproteins. To examine the changes in sialylation of CML granulocytes further, we have studied membrane preparations from CML and normal granulocytes for specific sialyltransferase activity. Because sialyltransferase enzymes are specific for the configuration of the acceptor group, enzyme activity was assayed by measuring transfer of sialic acid from CMP-14C-sialic acid to substrates of defined structure. As compared with those of normal counterparts, CML extracts catalyzed a 50% higher overall rate of sialylation of asialofetuin, a substrate possessing both N- and O-linked acceptors. Studies of enzyme specificity utilizing porcine and ovine submaxillary mucins, antifreeze glycoprotein and alpha-1 acid glycoprotein as acceptors showed that the increased sialylation by CML extracts was due primarily to substrates with the O-linked Gal beta 1----3GaINAc acceptor group. These data suggest that sialyltransferase activity is increased in CML granulocytes compared to normal granulocytes and that the increased enzyme activity is specific for O-linked Gal beta 1----3GaINAc. This enzyme activity may be directly responsible for the abnormal membrane sialylation and pathophysiological behavior of these cells.
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PMID:Increased activity of a specific sialyltransferase in chronic myelogenous leukemia. 241 27

The presence in the 100,000 g supernatant of rat brain homogenate of an inhibitor of the sialyltransferase has been confirmed. It is also present in chicken and bovine brain and in other rat and bovine organs. The inhibitor has been purified, a preparation with a specific activity 130-fold higher than that of the original 100,000 g supernatant of brain being obtained. It runs as a single peak in polyacrylamide-gel electrophoresis; when run in the presence of SDS, two components appeared. The apparent Mr of the components were 14,800 and 22,400. The inhibitor has been characterized as a heat-stable protein of acidic nature. It has effect on the glycolipid and the glycoprotein sialyltransferase activities but has no effect on the galactosaminyltransferase activity.
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PMID:Purification and characterization of an endogenous inhibitor of the sialyltransferase CMP-N-acetylneuraminate: lactosylceramide alpha 2,6-N-acetylneuraminyltransferase (EC 2.4.99.-). 246 92


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