Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.99.10 (sialyltransferase)
 1,547 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Porcine liver microsomes are capable of transferring sialic acid from CMP-NeuAc to [14C]galactosylated ovine submaxillary asialo-mucin, porcine submaxillary asialo/afuco-mucin and ganglioside GM1. The specificity of the porcine liver sialyltransferase (CMP-N-acetylneuraminate: D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) towards the first acceptor, [14C]Gal-GalNAc-protein, was investigated by means of methylation studies on the oligosaccharides changes cleft-off from the sialylated product glycoprotein by beta-elimination under reductive conditions. It appeared that sialic acid was transferred solely to position C-3 of galactose residues on Gal beta(1 leads to 3)GalNAc disaccharide units. Transfer to GalNAc residues was completely absent. Competition experiments and heat activation studies suggested that the same enzyme also converts ganglioside GM1 to ganglioside GD1a. Therefore, this porcine liver sialyltransferase can be designated as a Gal beta(1 leads to 3)GalNAc-R alpha(2 leads to 3) sialyltransferase.
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PMID:Specificity of porcine liver gal beta (1 leads to 3)galnac-r alpha(2 leads to 3) sialyltransferase sialylation of mucin-type acceptors and ganglioside GM1 in vitro. 728 98

Gal beta-1,4-GlcNAc alpha 2,6-sialyltransferase (CMP-N-acetylneuraminate:beta-galactoside alpha 2,6 sialyltransferase, EC 2.4.99.1) is a glycoprotein containing carbohydrate chains of the complex type (Jamieson, J.C. (1989) Life Sci. 43, 691-697). The carbohydrate chains may be important for controlling the expression of sialyltransferase catalytic activity during transit of the enzyme from the rough endoplasmic reticulum to the Golgi complex where it is active as a membrane bound enzyme anchored to the luminal face. To study the role of the carbohydrate chains of sialyltransferase for enzyme activity, conditions were established in which the native enzyme was deglycosylated with N-Glycanase and endo F. It was found that Glycanase removed the carbohydrate chains from native sialyltransferase, but methanol or ethanol had to be present for rapid and complete deglycosylation. Presence of methanol or ethanol were not essential for removal of carbohydrate chains with endo F. There was a correlation between the loss of catalytic activity of sialyltransferase with increased deglycosylation. After deglycosylation with Glycanase for 18 h catalytic activity was largely eliminated and there was a reduction in molecular mass of about 5 kDa compared to the untreated enzyme when examined by immunoblot analysis; this reduction was identical to that found when the denatured enzyme was deglycosylated with Glycanase. At shorter times of incubation partially deglycosylated forms of the enzyme were detected. Complete deglycosylation of native or denatured sialyltransferase with endo F could not be achieved. However, incubation with endo F for 24 h resulted in a loss of catalytic activity of about 60%. Immunoblot analysis showed the presence of three forms of the enzyme corresponding in molecular mass to the native and deglycosylated enzyme and a third form corresponding to a partially deglycosylated enzyme. Sialyltransferase was also subjected to sequential treatment with exoglycosidases. Removal of NeuAc and Gal had little effect on catalytic activity, but subsequent removal of GlcNAc resulted in a significant loss in catalytic activity suggesting that the presence of the trimannose core with GlcNAc attached is important for the expression of catalytic activity. The presence of organic solvents during deglycosylation with Glycanase may be a useful method that can be applied to other glycoproteins.
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PMID:The role of the carbohydrate chains of Gal beta-1,4-GlcNAc alpha 2,6-sialyltransferase for enzyme activity. 839 96

The dependence of CMP-N-acetylneuraminate:GM1 sialyltransferase (SAT IV) activity of rat liver Golgi apparatus on GM1 ganglioside ceramide composition was evaluated. SAT IV activity was assayed on GM1 molecular species carrying homogeneous ceramide moieties containing long chain bases of different length (18 or 20 C atoms) unsaturated or not, linked to 14:0, 16:0, 18:0 or 22:0 fatty acids. The results obtained in the presence of the detergent Triton CF-54, when enzyme and substrate are presumably part of the same supramolecular structure, show that either the long chain base or the fatty acid composition can affect enzyme activity. This feature was not displayed when GM1 was embedded in dipalmitoylphosphatidylcholine vesicles in the absence of detergent. Under the latter conditions, the enzyme was not sensitive to the lipid composition of GM1 but to the ganglioside/phospholipid ratio in the vesicles. These results indicate for the first time that SAT IV is affected by the lipid composition of the substrate and strengthen the hypothesis that glycosyltranferases may contribute to control the cellular glycosphingolipid ceramide pattern.
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PMID:Dependence of rat liver CMP-N-acetylneuraminate:GM1 sialyltransferase (SAT IV) activity on the ceramide composition of GM1 ganglioside. 892

A mechanistic study of rat liver alpha-(2-->6) sialyltransferase (ST) is presented that includes isotope trapping experiments and kinetic isotope effects on V/K for the ST-catalyzed reaction of isotopically labeled CMP-N-acetylneuraminate and N-acetyllactosamine. The isotope trapping experiments confirmed that the kinetic mechanism is steady-state random, and further analysis indicated that for this sialyltransferase the experimentally observed isotope trapping ratio (product trapped/substrate released) was equivalent to the commitment to catalysis, Cf, the quantity required to correct the kinetic isotope effects. Cf was found to range from 1.0 (at 1.6 mM LacNAc) to 1.7 (at 100 mM LacNAc). After correction for Cf, the isotope effects were as follows: secondary beta-dideuterium, 1.04-1. 05; anomeric carbon primary 14C, 1.000 +/- 0.004; a small 3H binding effect of 1.016 +/- 0.007 at C9; and a carboxylate carbon secondary 14C isotope effect of 0.998 +/- 0.004. This pattern of KIEs is quite different than observed for solvolysis of CMP-NeuAc [Horenstein, B. A., and Bruner, M. (1996) J. Am. Chem. Soc. 118, 10371-10379]. Based on the results of ab-initio modeling of isotope effects, a hypothesis is presented which reconciles the unusual pattern of KIEs on the basis of binding interactions at the carboxylate carbon.
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PMID:Isotope trapping and kinetic isotope effect studies of rat liver alpha-(2-->6)-sialyltransferase. 942 50


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