title: Characterization of sialyltransferase-IV activity and its involvement in the c-pathway of brain ganglioside metabolism.
abstract: 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)
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298.
authors.forename: B
authors.initials: B
authors.lastname: Freischütz
authors.forename: M
authors.initials: M
authors.lastname: Saito
authors.forename: H
authors.initials: H
authors.lastname: Rahmann
authors.forename: R K
authors.initials: RK
authors.lastname: Yu
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D001923:Brain Chemistry; D002793:Cholic Acids / Q000494:pharmacology; D005260:Female; D005732:Gangliosides / Q000032:analysis / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D017830:Octoxynol / Q000494:pharmacology; D010471:Perches; D051381:Rats; D017207:Rats, Sprague-Dawley; D012799:Sialyltransferases / Q000032:analysis* / Q000378:metabolism / Q000502:physiology*
chemical_list: D002793:Cholic Acids; D005732:Gangliosides; C033851:ganglioside, GD1b; D008345:Manganese; C016481:trisialoganglioside GT1; C039129:GQ1b ganglioside; D017830:Octoxynol; D012799:Sialyltransferases; D008274:Magnesium; C028213:3-((3-cholamidopropyl)dimethylammonium)-1-propanesulfonate