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)

Competition experiments using lactosylceramide, ganglioside GM3 and ganglioside GD3 as substrates, as well as mutual inhibitors for ganglioside N-acetylgalactosaminyltransferase, in Golgi vesicles derived from rat liver suggested that N-acetylgalactosamine transfer to these three respective compounds, leading to gangliosides GA2, GM2, and GD2, respectively, is catalyzed by one enzyme. Analogous studies with gangliosides GA1, GM1, and GD1b as glycolipid acceptors in sialyltransferase assays indicated GM1b, GD1a, and GT1b synthases to be identical. These results are incorporated into a model for ganglioside biosynthesis and its regulation.
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PMID:Both GA2, GM2, and GD2 synthases and GM1b, GD1a, and GT1b synthases are single enzymes in Golgi vesicles from rat liver. 314 Feb 34

In order to better understand the role of cell surface glycolipids in T lymphocyte activation, heparin was used to simultaneously modulate the expression of glycolipids and the lytic capacity of lymphocytes activated by interleukin-2. Results presented here show that heparin added at the start of a 3 day culture inhibited the formation of lymphokine activated killer cells by up to 50%. Heparin also has a profound effect on the synthesis of glycolipids during this three day period. Asialo GM1, a useful cell surface marker for subsets of murine cytotoxic cells, is reduced in amount, as are the other two major neutral glycolipids lactosylceramide and asialo GM2. In addition, the synthesis of some gangliosides is affected by heparin treatment. Comparison of the glycosyltransferase activities of untreated and heparin-treated cells shows that the activities of a 2-3-sialyltransferase and a beta 1-3 galactosyltransferase are inhibited dramatically, while a third enzyme, N-acetyl-galactosaminyltransferase is unaffected. The two heparin inhibitable enzymes bind to heparin affinity columns but the galactosaminyltransferase does not. These studies suggest that the proper regulation of the activities of specific glycosyltransferases may be important events in lymphocyte activation.
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PMID:Heparin inhibits specific glycosyltransferase activities in interleukin 2 activated murine T cells. 314 30

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

It was previously reported that monosialosylgangliopentaosyl ceramide (GalNAc-GM1b) was a major ganglioside in Xenopus laevis oocytes. Here we determined biosynthetic pathways for the ganglioside by detailed measurements of glycosyltransferase activities. CMP-NeuAc:asialo-GM1 alpha 2-3 sialyltransferase (alpha 2-3 ST) and UDP-GalNAc:GM1b beta 1-4 N-acetylgalactosaminyltransferase (beta 1-4 GalNAcT) exhibited much higher activity than CMP-NeuAc:GalNAc-GA1 alpha 2-3 ST and UDP-GalNAc:asialo-GM1 beta 1-4 GalNAcT, respectively. These observations indicated the existence of a unique biosynthetic pathway in the oocytes as follows; asialo-GM1-->GM1b-->GalNAc-GM1b.
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PMID:A unique biosynthetic pathway for gangliosides exists in Xenopus laevis oocytes. 792 15

The in vitro activity of sialyltransferase IV (SAT-IV), which catalyzes the transfer of sialic acid to the terminal galactose of different gangliotetraosylceramides (GA1, GM1a and GD1b), was examined in membrane-enriched preparations from mouse embryos at embryonic day 12 (E-12). Gangliosides GD1a and GT1b were the only reaction products using GM1a and GD1b as substrates, respectively. The Km values for GM1a and GD1b were 53 microM and 42 microM, respectively. Competitive inhibition experiments showed that the same enzyme (SAT-IV) catalyzed sialic acid transfer to the terminal galactose residues of both GM1a and GD1b. Two labeled ganglioside products were obtained, however, using GA1 as a substrate. One product was identified as ganglioside GM1b and the enzymatic reaction for its formation was maximal at pH 6.0, similar to that for GD1a and GT1b formation. The second product, synthesized by a different sialyltransferase, was identified as GD1 alpha based on results from TLC immunostaining, neuraminidase digestion, and periodate oxidation-borohydride reduction. The pH dependence curve for GD1 alpha formation had a different shape than that for GM1b formation with a maximum at pH 6.3. GD1 alpha is apparently synthesized from GM1b by an endosialyltransferase that catalyzes the transfer of a second sialic acid to the internal N-acetylgalactosamine of GM1b. The formation of both GM1b and GD1 alpha was linear over protein concentration. The ratio of GD1 alpha/GM1b formation varied from 0.25 to 1.20 depending on the GA1 substrate concentration.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Ganglioside biosynthesis in mouse embryos: sialyltransferase IV and the asialo pathway. 807 55