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:2.4.99.7 (sialyltransferase)
1,534 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have examined granulocytes from patients with chronic myelogenous leukemia (CML) and from normal subjects to determine whether activity of a specific sialyltransferase might account for the aberrant sialylation of O-linked membrane oligosaccharides in CML cells. Total membrane preparations of morphologically mature CML and normal granulocytes were tested for sialyltransferase activity using the substrates galactosyl-beta 1-3-N-acetyl-D-galactosamine-alpha-O-nitrophenyl and N-acetyl-D-galactosamine-alpha-phenyl. N-Acetyl-D-galactosamine-alpha-phenyl was not an acceptor with either CML or normal cells. With galactosyl-beta 1-3-N-acetyl-D-galactosamine-alpha-O-nitrophenyl, sialyltransferase activity was 2.8 times higher in CML cells compared to normal cells. Product identification by high performance liquid chromatography showed that enzyme from both normal and CML granulocytes linked sialic acid to galactosyl-beta 1-3-N-acetyl-D-galactosamine-R by the alpha(2-3) and not the alpha(2-6) linkage. The enzyme CMP-N-acetylneuraminic acid: galactosyl-beta 1-3-N-acetyl-D-galactosamine-R alpha(2-3)-sialyltransferase has not previously been described in human granulocytes. The marked increase in activity of this enzyme in CML and the resulting increase in sialylation may contribute to the pathophysiological behavior of CML granulocytes.
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PMID:Presence of cytidine 5'-monophospho-N-acetylneuraminic acid:Gal beta 1-3GalNAc-R alpha(2-3)-sialyltransferase in normal human leukocytes and increased activity of this enzyme in granulocytes from chronic myelogenous leukemia patients. 347 17

Using 500-MHz 1H NMR spectroscopy we have investigated the branch specificity that bovine colostrum CMP-NeuAc:Gal beta 1----4GlcNAc-R alpha 2----6-sialyltransferase shows in its sialylation of bi-, tri-, and tetraantennary glycopeptides and oligosaccharides of the N-acetyllactosamine type. The enzyme appears to highly prefer the galactose residue at the Gal beta 1----4GlcNAc beta 1----2Man alpha 1----3 branch for attachment of the 1st mol of sialic acid in all the acceptors tested. The 2nd mol of sialic acid becomes linked mainly to the Gal beta 1----4GlcNAc beta 1----2Man alpha 1----6 branch in bi- and triantennary substrates, but this reaction invariably proceeds at a much lower rate. Under the conditions employed, the Gal beta 1----4GlcNAc beta 1----6Man alpha 1----6 branch is extremely resistant to alpha 2----6-sialylation. A higher degree of branching of the acceptors leads to a decrease in the rate of sialylation. In particular, the presence of the Gal beta 1----4GlcNAc beta 1----6Man alpha 1----6 branch strongly inhibits the rate of transfer of both the 1st and the 2nd mol of sialic acid. In addition, it directs the incorporation of the 2nd mol into tetraantennary structures toward the Gal beta 1----4GlcNAc beta 1----4Man alpha 1----3 branch. In contrast, the presence of the Gal beta 1----4GlcNAc beta 1----4Man alpha 1----3 branch has only minor effects on the rates of sialylation and, consequently, on the branch preference of sialic acid attachment. Results obtained with partial structures of tetraantennary acceptors indicate that the Man beta 1----4GlcNAc part of the core is essential for the expression of branch specificity of the sialyltransferase. The sialylation patterns observed in vivo in glycoproteins of different origin are consistent with the in vitro preference of alpha 2----6-sialyltransferase for the Gal beta 1----4GlcNAc beta 1----2Man alpha 1----3 branch. Our findings suggest that the terminal structures of branched glycans of the N-acetyllactosamine type are the result of the complementary branch specificity of the various glycosyltransferases that are specific for the acceptor sequence Gal beta 1----4GlcNAc-R.
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PMID:Branch specificity of bovine colostrum CMP-sialic acid: Gal beta 1----4GlcNAc-R alpha 2----6-sialyltransferase. Sialylation of bi-, tri-, and tetraantennary oligosaccharides and glycopeptides of the N-acetyllactosamine type. 354 84

Monolayers of hepatocytes attached on collagen-coated dishes were cultured for 20-24 h and were found suitable to study the activity and secretion of CMP-N-acetylneuraminate:asialo-alpha 1-acid glycoprotein sialyltransferase. A progressive increase of sialyltransferase activity in the culture medium was observed during incubation of the hepatocytes. After 24 h 34-48% of the total sialyltransferase activity of the hepatocyte incubation system was present in the medium. The enzyme activity present in the medium was soluble in nature and could not be stimulated by Triton X-100. The secretion of the enzyme was stimulated about twofold by dexamethasone. The activity of sialyltransferase in the hepatocytes was also increased by dexamethasone. The Km of either hepatocyte or medium sialyltransferase for CMP-sialic acid was only slightly changed by dexamethasone, whereas the Vmax was increased about twofold. The secretion of sialyltransferase could be inhibited partially by the anti-microtubular agent colchicine. The dexamethasone-induced increase of the sialyltransferase activity in cells and media could be eliminated by inclusion of alpha-amanitin in the culture media at 0 h. The inhibiting effect of alpha-amanitin was only partially expressed when the drug was added 4 h after the addition of dexamethasone to the media. The results suggest that isolated rat hepatocytes actively secrete sialyltransferase and that the increase in the sialyltransferase activity in cells and media owing to the synthetic glucocorticosteroid dexamethasone results from increased synthesis of the enzyme molecule. It is supposed that in the intact rat the increased levels of the enzyme activity in serum observed in inflammation may originate from an induction of the synthesis of sialyltransferase in the hepatocytes of rat liver by the increased levels of circulating corticosteroids.
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PMID:Activity and secretion of sialyltransferase in primary monolayer cultures of rat hepatocytes cultured with and without dexamethasone. 371 1

The effects of phytohemagglutinin (PHA) stimulation on the activities of sialyltransferase 1 (SAT-1), and sialyltransferase 3 (SAT-3), in human lymphocytes were investigated in vitro. For SAT-1 and SAT-3, respectively, the apparent Km values with variable CMP-NeuAc concentrations were 0.19 and 0.015 mM and with variable LacCer were 0.075 and 0.17 mM. Progressive increases in the activities of SAT-1 and SAT-3 were detected in lymphocytes stimulated with PHA, whereas no increase was observed in control lymphocytes incubated in culture medium alone. These increased activities occurred within 18-36 h of incubation and preceded optimum lymphocyte proliferation. Intact lymphocytes were needed for the lectin-stimulated increase of sialyltransferase activities because neither concanavalin A nor phytohemagglutinin added to the broken cell preparation modulated SAT-1 activity. The glycolipid products formed as a result of these enzymatic reactions in the presence of endogenous and exogenous acceptors were tentatively identified by thin-layer chromatography and autofluorography. The addition of exogenous LacCer to the SAT-1 assay resulted in the radiolabeling of a small amount of ganglioside GM1b (3.4%), but GM3 was the major labeled product (96%). When GgOse4Cer was added to the SAT-3 assay, 32% GM3 and 24.6% GM1b were detected while 44% consisted of glycolipids not labeled in assays performed without exogenous acceptors. Of the radioactivity transferred to endogenous acceptors, 81.3% was in GM3 and 14.6% in GM1b. These results demonstrate that the modulation of sialyltransferase activity occurs earlier than cellular activation.
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PMID:Effects of lectin activation on sialyltransferase activities in human lymphocytes. 371 65

Sialyltransferase activity of bovine serum with the acceptor asialofetuin exhibits a pH optimum at 6.0-6.5, no divalent cation dependence, and a Km for CMP-sialic acid of 0.05 mM. Although a 2-fold increase in sialyltransferase activity with the acceptor asialofetuin is observed in serum samples from 2-day-old vs 20-day-old calves, the relative activity towards other glycoprotein acceptors is not different between the groups. With the acceptor lactose, the major product (greater than 95%) for all samples is 3'-sialyllactose, suggesting that the elevated levels of sialyltransferase in 2-day-old calves are due to Gal-R (alpha 2-3) sialyltransferase.
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PMID:Sialyltransferase of bovine serum: age- and hormone-related changes. 374 24

A sialyltransferase involved in the biosynthesis in vitro of LD1c (NeuAc alpha 2-8NeuGc alpha 2-3Gal beta 1-4Glc-NAc beta 1-3Gal beta 1-4Glc-Cer) has been characterized from 9 to 11-day-old embryonic chicken brains. The CMP-[14C]NeuAc:LM1(alpha 2-8)sialyltransferase (SAT-2) sedimented (75%) at the junction of 0.75 and 1.2 M on a discontinuous sucrose density gradient when still membrane bound. In addition to the biosynthesis of LD1c, the detergent-solubilized (0.4% Nonidet P-40) preparation also catalyzes the transfer of sialic acid to O-8 of sialic acid in GM3 to form GD3 (NeuAc alpha 2-8NeuAc alpha 2 - 3Gal beta 1 - 4Glc - Cer). Substrate inhibition studies indicated that these two reactions are probably catalyzed by the same enzyme, SAT-2. The kinetic parameters of SAT-2 activity were determined. The Km values were 70 and 63 microM with CMP-[14C]NeuAc and LM1, respectively, when the detergent-solubilized supernatant fraction was used as enzyme source. The (alpha 2-8)-linkage between the terminal and penultimate sialic acids was determined using nonradioactive CMP-NeuAc and [Ac-14C]LM1 as substrates (Higashi, H., and Basu, S. (1982) Anal. Biochem. 120, 159-164) for the enzyme, followed by identification of the permethylated [14C]sialic acid of the product by radioautography. At 0.5 mM N-ethylmaleimide, the SAT-2 activity was inhibited 50% whereas SAT-1 and SAT-3 activities (Basu, M., Basu, S., Stoffyn, A., and Stoffyn, P. (1982) J. Biol. Chem. 257, 12765-12769) remained uninhibited.
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PMID:Biosynthesis in vitro of disialosylneolactotetraosylceramide by a solubilized sialyltransferase from embryonic chicken brain. 383 72

Peptide maps of Form A and Form B of porcine submaxillary gland beta Gal alpha 2----3 sialyltransferase were essentially identical, consistent with the view that the two forms are not different enzyme species but that one, the B form (Mr = 44,000) is derived from the A form (Mr = 49,000). Analysis of the sialyltransferase activity in subcellular fractions from homogenates of porcine submaxillary glands reveals that 85% of the total activity of the transferase is bound to membranes, mostly in the Golgi apparatus, and that the remainder is soluble. The relative amounts of the membrane-bound and soluble forms as well as their response to detergents suggests that they are the cellular counterparts to the A and B forms of the transferase. The activity of Form A and the membrane-bound enzyme is stimulated to similar extents by various detergents. Triton-type detergents are more effective than Brij-type. Lysophosphatidylcholine is a potent stimulator of the activity of Form A but lysophosphatidylethanolamine is without effect and lysophosphatidylserine and lysophosphatidylglycerol are inhibitory. C16-18 acyl derivatives of lysophosphatidylcholine stimulate the activity more extensively than the C14 acyl derivative, and the C12 acyl derivative is without effect. In contrast, Form B is fully active in the absence of all detergents tested although it is inactivated just as Form A by lysophosphatidylglycerol and octylglucoside. Kinetic analysis of Forms A and B reveal that detergents stimulate the activity of Form A by lowering the KD and KM of CMP-NeuAc and increasing the Vmax of the reaction. Form B in contrast, which is fully active in the absence of detergents, has kinetic parameters like those of Form A in the presence of detergent. Taken together, these results suggest that Form A of the sialyltransferase, but not Form B, contains a lipid-binding domain, and that binding of detergents or lipids to the domain modulates the activity of the enzyme.
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PMID:Regulation of beta-D-galactoside alpha 2----3 sialyltransferase activity. The effects of detergents and lysophosphatidates. 385 Sep

By use of 500-MHz 1H NMR spectroscopy, the branch specificity of bovine colostrum CMP-NeuAc:Gal beta 1----4GlcNAc-R alpha 2----6-sialyltransferase towards a biantennary glycopeptide and oligosaccharides of the N-acetyllactosamine type, differing in completeness and structure of their core portion, was investigated. In agreement with earlier reports (Van den Eijnden, D. H., Joziasse, D. H., Dorland, L., Van Halbeek H., Vliegenthart, J. F. G., and Schmid, K. (1980) Biochem. Biophys. Res. Commun. 92, 839-845), it appears that the enzyme strongly prefers the galactosyl residue at the Man alpha 1----3Man branch of the biantennary glycopeptide for attachment of the first sialic acid residue. This branch specificity is fully preserved with the structure (formula; see text) Reduction of the reducing N-acetylglucosaminyl residue in this structure, however, leads to a decreased branch specificity, whereas removal of this residue results in a random attachment of sialic acid to the galactoses at both branches. The decrease in branch specificity is accompanied by a reduction in the rate of sialic acid transfer to the galactose at the alpha 1----3 branch. Our results indicate that the presence of the aforementioned N-acetylglucosaminyl residue is a minimal structural requirement for branch specificity of the sialyltransferase. We propose that in the interaction of the sialyltransferase with its substrates, this N-acetylglucosaminyl residue functions as a recognition site mediating the correct positioning of the substrate on the enzyme.
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PMID:Branch specificity of bovine colostrum CMP-sialic acid: N-acetyllactosaminide alpha 2----6-sialyltransferase. Interaction with biantennary oligosaccharides and glycopeptides of N-glycosylproteins. 388 25

A sialyltransferase which catalyzes the in vitro biosynthesis of N-acetylneuraminosyllacto-N-neohexaosylceramide from lacto-N-neohexaosylceramide and CMP-NeuAc has been examined in embryonic chicken breast muscle. The maximum enzyme activity was observed in 11-12-day-old embryos. The enzyme has optimum activity at pH 6.8 in the presence of Triton CF-54 and Mg2+. The apparent Km values for lacto-N-neohexaosylceramide and CMP-NeuAc were 0.9 and 0.67 mM, respectively. The enzymic product was characterized by TLC, neuraminidase hydrolysis and permethylation analysis. The structure was identical to authentic N-acetylneuraminosyllacto-N-neohexaosylceramide from chicken muscle. In addition, a disialo derivative has been detected that constitutes 15% of the total radioactivity incorporated. The two sialic acids connected by sialosyl-sialosyl linkage were attached to the terminal galactose residue. To our knowledge, this is the first report of biosynthesis of this disialo compound.
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PMID:Sialylation of lacto-N-neohexaosylceramide by sialyltransferase from embryonic chicken muscle. 395 72

The activities of ten enzymes involved in sialic acid metabolism were measured in colonic mucosal cells from rats and compared with those in liver. A methodology was devised that enabled all ten enzyme activities to be evaluated in a single rat colon preparation. Enzyme assays with radioactively labelled substrates were developed for maximum sensitivity, and the identification of substrates and products was carefully checked to assess the contribution of contaminants to enzyme reactions with low activity. The activities of most enzymes involved in the biosynthesis of N-acetyl-D-neuraminic acid (NeuAc) from UDP-N-acetyl-D-glucosamine were found to be more than 20-fold lower than those in liver. The activities of CMP-NeuAc synthase, N-acetyl-D-glucosamine 2-epimerase, N-acetyl-D-glucosamine kinase, sialyltransferase and sialidase were similar to or 2-4-fold lower than in liver. The biosynthesis of NeuAc via its 9-phosphate was demonstrated in the 100 000 g supernatant of colonic-cell homogenates by enzymic assay and precursor experiments with N-acetyl[14C]-mannosamine. No alternative route for NeuAc formation could be detected. The 100 000g supernatant fractions of liver, kidney and colonic mucosal cells utilized N-acetyl[14C]mannosamine with differing efficiencies. Radioactive products identified as sialic acid biosynthetic intermediates amounted to 49%, 0.04% and 5.6% of added precursor in liver, kidney and colon respectively. Catabolism of labelled precursor to non-hexosamine products was high in kidney and colonic mucosal-cell fractions.
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PMID:The metabolism of sialic acids in isolated rat colonic mucosal cells. 397 62


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