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)

Adipocytes treated with neuraminidase show markedly reduced responsiveness to insulin without any alteration in insulin binding. In addition, several studies have separately demonstrated both insulin resistance and decreases in membrane sialic acid content and associated biosynthetic enzymes in diabetes mellitus. In the present study, we investigated the role that sialic acid residues may play in insulin action and in the hepatic insulin resistance associated with nonketotic diabetes. Primary cultures of hepatocytes from normal rats treated with neuraminidase demonstrated a dose-dependent decrease in insulin-stimulated lipogenesis. At a concentration of neuraminidase that decreases insulin action by 50%, 23% of total cellular sialic acid content was released. Neuraminidase-releasable sialic acid was significantly decreased in hepatocytes from diabetic rats and this was associated with significant insulin resistance. Treatment of hepatocytes from diabetic rats with cytidine 5'-monophospho-N-acetylneuraminic acid (CMP-NANA) enhanced insulin responsiveness 39%. The enhanced insulin responsiveness induced by CMP-NANA was blocked by cytidine 5'-monophosphate (CMP) suggesting that the CMP-NANA effect was catalyzed by a cell surface sialyltransferase. CMP reduced neuraminidase-releasable [14C]sialic acid incorporation into hepatocytes by 43%. The data demonstrate a role for cell surface sialic acid residues in hepatic insulin action and support a role for decreased cell surface sialic acid residues in the insulin resistance of diabetes mellitus.
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PMID:Role of sialic acid in insulin action and the insulin resistance of diabetes mellitus. 340 69

Serum samples of 7 cows from -10 to +10 days following parturition and of 7 calves from 0 to 20 days following birth were tested for the ability to inhibit mitogen-stimulated proliferation of lymphocytes, for cortisol and progesterone concentrations, and for sialic acid and sialyltransferase activity. Calf serum inhibited phytohemagglutinin (PHA)-stimulated proliferation of lymphocytes, with maximal inhibition at 12-24 h following birth, whereas no consistent immunosuppressive activity was detected in the maternal serum. Sialic acid was greatly elevated in calf serum (4.8 +/- 0.2 mumol/ml) relative to adult control values (1.3 +/- 0.1) and decreased continuously from day 0 to day 20. Sialic acid of maternal serum was slightly elevated prior to parturition (1.7 +/- 0.1) and increased to peak at 2.5 +/- 0.1 on day 8 following parturition. Sialyltransferase of both maternal and calf serum increased dramatically following parturition to peak at day 2. For calf serum, a moderate correlation was observed between sialic acid and cortisol concentration (r = 0.71) and between sialic acid and suppression of PHA-stimulated proliferation (r = 0.60). The results demonstrate that serum of 12-24 h-old calves is immunosuppressive in vitro, and suggest that changes in sialic metabolism may accompany cortisol-related immunosuppression in these animals.
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PMID:Immunosuppression, sialic acid, and sialyltransferase of neonatal and maternal bovine serum. 382 Jan 92

Prokaryotic derived probes that specifically recognize alpha-2,8-ketosidically linked polysialosyl units were developed to identify and study the temporal expression of these unique carbohydrate moieties in developing neural tissue (Vimr, E. R., McCoy, R. D., Vollger, H. F., Wilkison, N. C., and Troy, F. A. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 1971-1975). These polysialosyl units cap N-linked oligosaccharides of the complex-type on neural cell adhesion molecules (N-CAM). A Golgi-enriched fraction from 20-day-old fetal rat brain contains a membrane-associated sialyltransferase that catalyzes the incorporation of [14C]N-acetylneuraminic acid [( 14C]NeuNAc) from CMP-[14C] NeuNAc into polymeric products. At pH 6.0, 84 pmol of NeuNAc mg of protein-1 h-1 were incorporated. In sodium dodecyl sulfate-polyacrylamide gels, the major radiolabeled species migrated with a mobility expected for N-CAM. A bacteriophage-derived endoneuraminidase specific for polysialic acid was used to demonstrate that at least 20-30% of the [14C]NeuNAc was incorporated into alpha-2,8-linked polysialosyl units. This was confirmed by structural studies which showed that the endoneuraminidase-sensitive brain material consisted of multimers of sialic acid. The addition of a partially purified preparation of chick N-CAM to the membranous sialyltransferase stimulated sialic acid incorporation 3-fold. The product of this reaction was also sensitive to endoneuraminidase and contained alpha-2,8-linked polysialosyl chains, thus showing that N-CAM can serve as an exogenous acceptor for sialylation in vitro. Sialic acid incorporated into adult rat brain membranes was resistant to endoneuraminidase, indicating that the poly-alpha-2,8-sialosyl sialyltransferase activity is restricted to an early developmental epoch. It is recommended that the enzyme described here be designated CMP-NeuNAc:poly-alpha-2,8-sialosyl sialyltransferase and the trivial name poly-alpha-2,8-sialosyl sialyltransferase be adopted.
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PMID:CMP-NeuNAc:poly-alpha-2,8-sialosyl sialyltransferase and the biosynthesis of polysialosyl units in neural cell adhesion molecules. 404 5

Human erythrocyte T & NN antigens were exposed to fresh sera from single human donors and CMP-[14C]sialic acid without activators in a single 24 hr incubation at 37 degrees C. There was similar sialic acid (NAN) uptake, on the average 2.7 mol/mol T antigen subunit (mol wt 40,000), with various NN- and MM-derived T antigens and transferase sera in all different combinations. Sera from donors with the M gene but not from those lacking it incorporated NAN into NN antigen (c. 1 mol NAN/mol NN antigen subunit, mol wt 50,000). The profound difference in sialyltransferase action between sera from donors with the M gene and those lacking it was substantiated by repeated incubations of NN-derived T antigen with CMP-NAN and MM donor transferase serum, which incorporated 32% more NAN than did repeated incubations of the same antigen with CMP-NAN and NN donor transferase serum. The greater NAN incorporation by sera of donors with the M gene is due to an additional transferase-modifier substance present only in persons possessing the M gene.
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PMID:Sialylation of Thomsen-Friedenreich (T) and blood type NM antigens by transferases in human sera measured by [14C]NAN uptake. 615 12

GMP-N-Acetylneuraminate: galactosyl-glycoprotein sialytransferase (CMP-N-acetylneuraminate: D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) activity was identified in the human cervical epithelium. The enzyme has a pH optimum of 6.0, a temperature optimum of 28 degrees C, and demonstrates a partial requirement for Triton X-100. Michaelis constants for asialofetuin and CMP-N-acetyl[14C]neuraminic acid are 0.64 . 10(-5) M (expressed as the concentration of terminal galactose residues) and 2.05 . 10(-5) M, respectively. Sialytransferase demonstrated minimal affinity for the low molecular weight acceptors tested, and may have a requirement for a glycoprotein acceptor having a terminal N-acetyllactosamine (Gal beta (1 leads to 4)GlcNAc) type structure. Cytidine nucleotides are potent inhibitors of the sialyltransferase reaction; CMP acts as a competitive inhibitor.
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PMID:Glycosyltransferases of the human cervical epithelium. II. Characterization of a CMP-N-acetylneuraminate: galactosyl-glycoprotein sialyltransferase. 616 92

Sialic acid metabolism was investigated in the livers of control rats and of rats treated with a single oral dose (1.5 ml/kg body weight) of carbon tetrachloride. The main change observed during the necrotic stage of CCl4 poisoning (18 h after treatment) was a highly significant reduction in sialyltransferase activity. Slight reciprocal changes in neuraminidase activities, i.e., a small decrease in cytosolic neuraminidase and a small increase in the membrane bound enzyme were also observed. At 72 h after CCl4 treatment, during the stage of liver regeneration, the main change was a marked elevation in membrane-bound neuraminidase (two fold above control values). Moderate increases in the specific activities of CMP-N-acetylneuraminic acid synthetase and sialyltransferase were also observed. A considerable decrease in the sialic acid content of the isolated smooth endoplasmic reticulum (one half of control values) was detected at 72 h after CCl4 administration. The sialic acid content of the rough endoplasmic reticulum, on the other hand, remained at control levels.
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PMID:Sialic acid metabolism in rat liver: effect of carbon tetrachloride. 664 93

The specific activities of UDP-galactose : GM2 galactosyltransferase and CMP-NAN : GM1 sialyltransferase were measured in total particulate fractions of individual hepatocellular carcinomas (hepatomas) and hepatic nodules, induced in the rat by a carcinogenic diet of 0.05% N-2-fluorenylacetamide alternating with a low protein basal diet. In all tumors except the smallest nodules, galactosyltransferase specific activities were increased compared to those of control livers from rats fed only basal diet. When relative specific activities were related to wet weight of nodules larger than 0.1 g were in two populations. Specific activities of nodules in one population overlapped those of poorly differentiated hepatomas whereas specific activities of the second population those of well differentiated hepatomas. Specific activities of the sialyltransferase were also increased above those in control livers but not with the same frequency or to the same extent as for the galactosyltransferase. As with galactosyltransferase, nodules were found in two major populations when specific activities were related to nodule wet weight. The data suggest that increased specific activities of galactosyltransferase and sialyltransferase in hepatic nodules may provide an early phenotypic indicator of diverging differentiation in hepatocarcinogenesis.
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PMID:Gangliosides of liver tumors induced by N-2 fluorenylacetamide III. Galactosyl and sialyl transferases in single carcinomas and nodules. 677 33

Membranous sialyltransferase complexes from Escherichia coli K-235 catalyze the synthesis of surface polymers containing alpha-2,8-ketosidically linked polysialic acid. Undecaprenyl phosphate functions as an intermediate carrier of sialic acid (NeuNAc) residues between cytidine 5'-monophospho-N-acetylneuraminic acid (CMP-NeuNAc) and an endogenous acceptor (Troy, F.A., and McCloskey, M.A. (1979) J. Biol. Chem 254, 7377-7387). In vitro pulse-chase experiments now confirm that polymer elongation occurs by the addition of sialyl residues to the nonreducing termini of growing nascent chains. Sequential periodate oxidation and borohydride reduction of radiolabeled polysialic acid was used to quantitatively convert the terminal, nonreducing sialic acid to the 7-carbon analogue, 5-acetamido-3,5-dideoxy-L-arabino-2-heptulosonic acid (NeuNAc7). After complete hydrolysis of the polymers by neuraminidase, the ratio between NeuNAc and NeuNAc7 was used to determine the average degree of polymerization (D.P.). The membrane preparations used as a source of enzyme contained endogenous sialyl polymers that averaged 165 residues in length. During the first phase of in vitro synthesis, lasting about 90 min, 40 to 45 sialyl residues were transferred onto these endogenous acceptors. Subsequent in vitro incorporation increased at a slower, constant rate for at least 16 h. During this second phase of synthesis, the D.P. of newly synthesized chains remained relatively constant while the number of nonreducing terminal end groups, a measure of the number of new sialyl chains, increased. These results establish that individual polymer chains are rapidly elongated in vitro to a defined length of about 200 sialyl residues, then terminated and new chains started. The mechanism signaling chain termination, translocation of the sialyltransferase to a new acceptor, and chain reinitiation remains to be determined. Endogenous and enzymatically synthesized sialyl polymers were solubilized with Triton X-100 and purified to apparent homogeneity. Sialic acid accounted for approximately 93% of the mass of these polymers which had no free reducing terminal sialic acid. This position of the molecule is presumably occupied by an as yet unidentified component which links the sialyl polymer to the membrane.
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PMID:Structure and biosynthesis of surface polymers containing polysialic acid in Escherichia coli. 698 20

Sialic acid metabolism was investigated in control rat liver, in regenerating liver at 24 h and 48 h after partial hepatectomy and in the liver of sham-operated animals. High levels of membrane-bound neuraminidase, with no detectable changes in the soluble enzyme, were observed in regenerating rat liver. The neuraminidase activities in the liver of sham-operated rats were identical to those present in control liver. High levels of CMP-N-acetylneuraminic acid synthetase and sialyltransferase were observed both in regenerating liver as well as in the liver of sham-operated rats. The sialic acid content of regenerating rat liver, which was lower than that found in the liver of control and sham-operated rats at 24 h, returned to normal values 48 h after surgery.
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PMID:Sialic acid metabolism in regenerating rat liver. 730 57

A stable, sialyltransferase-deficient mutant of Neisseria gonorrhoeae strain F62 totally defective in CMP-NANA-dependent lipopolysaccharide (LPS) sialylation was isolated by insertion mutagenesis with transposon Tn 1545-delta 3 and screened for unlabelled colonies following incubation with CMP-14C-NANA. In contrast to the parental strain which became serum resistant on incubation with CMP-NANA or blood cell extracts, the mutant, JB1, remained serum sensitive. French press extracts of strain F62 catalysed LPS sialylation, but corresponding extracts of the mutant were inactive. Five LPS components were detected by SDS-PAGE in the parental strain. Five components of the same Mr were also found in the mutant. Three identical components were detected by Western blotting using MAb 3F11, which recognizes the Gal beta 1-4GlcNAc groups in the conserved LPS components of F62 which can be sialylated. The mutant, JB1, is therefore deficient in the sialyltransferase that is essential for both LPS sialylation and conversion of serum-sensitive gonococci to serum resistance by either CMP-NANA or blood cell extracts. No evidence was obtained for an LPS sialylation pathway by blood cell extracts that is independent of CMP-NANA.
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PMID:A serum-sensitive, sialyltransferase-deficient mutant of Neisseria gonorrhoeae defective in conversion to serum resistance by CMP-NANA or blood cell extracts. 756 13


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