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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)

A sialyltransferase activity which catalyzes the synthesis of the tetrasialoganglioside GQ1b (N-acetylneuraminyl-N-acetylneuraminylgalactosyl-N-acetylgalactosaminyl [N-acetylneuraminyl-N-acetylneuraminyl]-galactosylglucosylceramide) from added trisialoganglioside GT1b (N-=acetylneuraminylgalactosyl-N-acetylgalactosaminyl [N-acetylneuraminyl-N-acetylneuraminyl]galactosylglucosylceramide) and CMP-N-acetyl[4-14C]neuraminic acid has been demonstrated using a membrane fraction of embryonic chick brain. Optimum enzymatic activity was obtained using the detergent Triton CF-54 at a pH of 6.6. Enzyme activity appeared unaffected by Ca2+, Mg2+, Mn2+, EDTA, or histone. A slight elevation in activity was seen in the presence of Hg2+. When the disialoganglioside GD1b (galactosyl-N-acetylgalactosaminyl [N-acetylneuraminyl-N-acetylneuraminyl]galactosylglucosylceramide) was used as the glycolipid substrate, approximately 15% of the radioactive label was found in GQ1b. When this GQ1b was subjected to a periodate oxidation-borohydride reduction, the distribution of radioactive label was consistent with GQ1b being the major tetrasialoganglioside product and that its synthesis could proceed via the sequence GD1b-GT1b-GQ1b.
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PMID:In vitro biosynthesis of the tetrasialoganglioside GQ1b. 705 68

Asialomucin-sialyltransferase (CMP-N-acetylneuraminate:D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) activity was solubilized from mouse liver microsomes by sonication. The catalytic activity was markedly inhibited by a series of lysophosphatidylcholines, particularly 1-palmitoyl-sn-glycero-3-phosphorylcholine. This lysophospholipid did not alter optimal conditions for enzyme activity. In contrast, it was found that affinities for binding of Mn2+, desialylated mucin and CMP-sialic acid were decreased by adding the lipid. A reasonable interpretation of these data is that the presence of phospholipid modifies the enzyme conformation.
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PMID:Effects of 1-palmitoyl-sn-glycero-3-phosphorylcholine on the properties of a solubilized sialyltransferase activity from mouse liver. 712 92

To characterize the sialyltransferase-IV activity in brain tissues, the activities of GM1b-, GD1a-, GT1b-, and GQ1c-synthases in adult cichlid fish and rat brains were examined using GA1, GM1, GD1b, or a cod brain ganglioside mixture as the substrate. The GD1a-synthase activity in the total membrane fraction from cichlid fish brain required divalent cations such as Mg2+ or Mn2+ and Triton CF-54 for its full activity. The Vmax value was 1,340 pmol/mg of protein/h at an optimal pH of 6.5, whereas the apparent Km values for CMP-sialic acid and GM1 were 172 and 78 microM, respectively. Cichlid fish and rat brains also contained GM1b-, GT1b-, and GQ1c-synthase activities. The ratio of GM1b-, GD1a-, and GT1b-synthase activities in fish brain was 1.00:0.89:1.13, respectively, and in rat brain 1.00:0.60:0.63. Incubation of fish brain membranes with a cod brain ganglioside mixture, which contains GT1c, and [3H]CMP-sialic acid produced radiolabeled GQ1c. It is interesting that the adult rat brain also contains an appreciable level of GQ1c-synthase activity despite its very low concentrations of c-series gangliosides. The GD1a- or GQ1c-synthase activity in fish and rat brain was inhibited specifically by coincubation with the glycolipids that serve as the substrates for other sialyltransferase-IV reactions. Thus, the GD1a-synthase activity was inhibited by GA1 and GD1b, but not by LacCer, GM3, or GD3. In a similar manner, the synthesis of GQ1c was suppressed by GA1, GM1, and GD1b, but not by LacCer, GM3, or GD3.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Characterization of sialyltransferase-IV activity and its involvement in the c-pathway of brain ganglioside metabolism. 779 36

CMP-N-acetylneuraminic acid:lactosylceramide (alpha 2-3) sialyltransferase (GM3-synthase) was purified to homogeneity from a Triton CF-54 extract of young rat brain. The enzyme was separated by affinity chromatography on CDP-Sepharose column and resolved by linear NaCl gradient elution from the same adsorbent. Final purification of GM3-synthase was achieved by chromatography on a "lactosylceramide acid"-Sepharose column and specific elution with lactosylceramide. The enzyme activity was highest at pH 6.5 and required the presence of Triton CF-54 (0.15%) and Mn2+ (10 mM) for its full activity. The product of the reaction catalyzed by the enzyme was identified as GM3 based on its mobility on thin layer chromatographic plates using two different solvent systems. Comparison with several glycolipid substrates showed high specificity of GM3-synthase for lactosylceramide. The apparent Km value for lactosylceramide and CMP-N-acetylneuraminic acid were 80 and 210 microM, respectively. The apparent molecular mass of the enzyme determined on SDS-polyacrylamide gel electrophoresis was 76 kDa.
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PMID:Purification and characterization of CMP-N-acetylneuraminic acid:lactosylceramide (alpha 2-3) sialyltransferase (GM3-synthase) from rat brain. 825 49

A sensitive assay for sialyltransferase (STase activity extracted from gonococci with 0.5% Triton X100 was developed. Enzyme activity was optimal in the pH range 5.8-8.0 and was strongly inhibited by CMP, CDP and CTP, but not by other nucleotides, 10 mM Mg2+, Zn2+, Ca2+ or Mn2+, or by 18 mM EDTA. More than 90% of the activity was lost after 30 s at 67 degrees C. The apparent Vmax and apparent Km of the STase for cytidine 5'-monophospho-N-acetylneuraminic acid were 1.7 nmol of NANA incorporated/min/mg protein and 5.3 microM, respectively.
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PMID:Detection and some properties of the sialyltransferase implicated in the sialylation of lipopolysaccharide of Neisseria gonorrhoeae. 832 54

Rat liver Golgi membranes were found to contain an enzyme that can transfer sulphate from 3'-phosphoadenosine 5'-phosphosulphate (PAPS) to C-6 of the terminal GlcNAc in beta-linkage to mannose and has properties indicating that it is involved in the synthesis of the NeuAc alpha 2-3(6)Gal beta 1-4GlcNAc(6-SO4) sequences observed in the N-linked carbohydrate units of various glycoproteins. Assays performed with [35S]PAPS (Km 0.67 microM) and GlcNAc beta 1-6Man alpha 1-O-Me (GnMaMe) acceptor (Km 0.71 mM) indicated that the sulphotransferase had a pH optimum of approx. 7.0 and is markedly stimulated by Mn2+ ions (maximum approx. 15 mM) and Triton X-100 (0.05-0.1%). Hydrazine/nitrous acid/NaBH4 treatment of the 35S-labelled product yielded radiolabelled 2,5-anhydromannitol(6-SO4). The sulphated GnMaMc product of the GlcNAc-6-O-sulphotransferase could be galactosylated by a rat liver Golgi enzyme that was shown to have the same properties as the UDP-Gal:GlcNAc beta-1,4-galactosyltransferase from bovine milk. Competition studies performed with GlcNAc and GlcNAc-6-SO4 furthermore indicated that the same liver enzyme acted on both acceptors to produce Gal beta 1-4GlcNAc and Gal beta 1-4GlcNAc(6-SO4) with Km values of 1.04 and 1.68 mM respectively. Because the sulphated N-acetyl-lactosaminc could in turn serve as an acceptor for rat liver sialyltransferase, it seems that this enzyme, together with the Golgi galactosyltransferase and the GlcNAc-6-O-sulphotransferase, could act in concert in assembling the NeuAc alpha 2-3(6)Gal beta 1-4GlcNAc(6-SO4) branches of complex N-linked oligosaccharides.
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PMID:Characterization of a rat liver Golgi sulphotransferase responsible for the 6-O-sulphation of N-acetylglucosamine residues in beta-linkage to mannose: role in assembly of sialyl-galactosyl-N-acetylglucosamine 6-sulphate sequence of N-linked oligosaccharides. 887 Jun 71

The human alpha1,3-fucosyltransferase, Fuc-TVII, a key enzyme in the biosynthesis of selectin ligands, was expressed as a soluble protein-A chimeric form in a human B cell lymphoma cell line, Namalwa KJM-1, and purified using IgG-Sepharose. The enzymatic properties of recombinant soluble Fuc-TVII were then examined. Its enzyme activity was highest at pH 7.5, and the presence of 25 mM Mn2+ was required for full activity. Fuc-TVII exhibits an acceptor specificity restricted to alpha2,3-sialylated type 2 oligosaccharides, and the apparent Km values for alpha2,3-sialyl lacto-N-neotetraose and GDP-fucose were 3.08 mM and 16.4 microM, respectively. The inhibitory effects of various nucleotides on the activity of Fuc-TVII reflected its donor specificity for the nucleotide portion of GDP. Fuc-TVII was demonstrated to be useful for the synthesis of a sialyl Lewis x hexasaccharide from lacto-N-neotetraose in combination with an alpha2, 3-sialyltransferase, ST3Gal IV. Polyethylene glycols enhanced the thermal stability of Fuc-TVII, leading to increased formation of the reaction product.
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PMID:Enzymatic characterization of human alpha1,3-fucosyltransferase Fuc-TVII synthesized in a B cell lymphoma cell line. 940 91


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