Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.99.6 (sialyltransferase)
 1,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The subcellular distribution of polyisoprenyl pyrophosphate phosphatase activity has been examined in rat brain by assaying the release of 32Pi from [beta-32P]dolichyl pyrophosphate (Dol-P-P) as described previously (Scher,M.G. and Waechter, C.J. (1984) J. Biol. Chem., 259, 14580-14585). The highest specific activities of Dol-P-P phosphatase in rat brain were found in the Golgi-enriched light microsomal, synaptic plasma membrane and heavy microsomal fractions. A comparative analysis of the distribution of galactosyltransferase and dolichol kinase reveals that Dol-P-P phosphatase activity co-fractionates with galactosyltransferase activity, and that the high level found in the Golgi-enriched fraction is not due to cross-contamination with heavy microsomes. When beta-labelled C95 Dol-P-P and the C95 allylic polyisoprenyl pyrophosphate (Poly-P-P) were compared as substrates for the Golgi-enriched light microsomal and heavy microsomal fractions, similar Km values were calculated for the two pyrophosphorylated substrates for each membrane fraction. Based on these kinetic analyses, the enzyme(s) catalysing this reaction do not distinguish between substrates containing saturated or allylic alpha-isoprene units. When Dol-P-P phosphatase activity was assessed in submicrosomal fractions obtained from rat liver by two separate procedures, the highest specific activity was also detected in the Golgi-enriched fraction. While the specific activities for Dol-P-P phosphatase and sialyltransferase were in the relative order of Golgi greater than smooth endoplasmic reticulum (ER) greater than rough ER, the relative order of dolichol kinase was rough ER greater than smooth ER greater than Golgi.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Golgi-enriched membrane fractions from rat brain and liver contain long-chain polyisoprenyl pyrophosphate phosphatase activity. 166 43

Trypanosomatid protozoa are parasites of considerable medical and economic importance in developing countries. The pathway leading to N-glycosylation in these microorganisms is characterized by the following features: (i) dolichols are composed of only 10-13 isoprene units; (ii) oligosaccharides transferred in N-glycosylation have the compositions Man(6,7,9)GlcNAc2, depending on the species; (iii) trypanosomatids are unable to synthesize dolichol-P-Glc and, in addition, some species lack certain dolichol-P-Man-dependent mannosyltransferases; (iv) the oligosaccharyltransferase does not require the presence of glucose units in the oligosaccharide in order to catalyse an efficient transfer reaction; (v) trypanosomatids have a glucosidase II-like enzyme, but lack glucosidase I; (vi) glucosidase II is required for deglucosylation of oligosaccharides glucosylated by the UDP-Glc:glycoprotein glucosyltransferase, an activity first detected in those parasites; (vii) the structures of polymannose-type compounds in these protozoa have no significant differences with those of their mammalian counterparts except for the presence, in certain species, of oligosaccharides having galactofuranose units linked to external mannose residues; (viii) biantennary complex-type oligosaccharides having in some cases terminal alpha-linked galactose units or poly-N-acetylactosamine extensions, but lacking sialic acid units, have been described in Trypanosoma brucei; (ix) complex-type oligosaccharides having alpha-linked galactose, fucose and sialic acid residues have been described in Trypanosoma cruzi. In this parasite, addition of sialic acid units to glycoproteins and glycolipids is mediated by a trans-sialidase located on the external surface of the parasite and not by an intracellular CMP-sialic acid-dependent sialyltransferase.
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PMID:N-glycosylation in trypanosomatid protozoa. 835 46