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)

Golgi vesicle membranes from the Lec2 CHO glycosylation mutant translocate CMP-sialic acid at only 2% the rate of vesicles from wild-type CHO cells. The deficiency is specific, because vesicles from Lec2 cells can translocate UDP-N-acetylglucosamine, adenosine 3'-phosphate 5'-phosphosulfate, and UDP-galactose at rates comparable to those of vesicles from wild-type cells. Complementation analyses show that Lec2 mutants belong to the same genetic complementation group as clone 1021, a CHO mutant of similar phenotype. Both mutants have previously been shown to have a 90% reduction in the sialylation of glycoproteins and gangliosides compared with wild-type cells. However, 1021 cells appear to have normal levels of CMP-sialic acid, sialyltransferase activity, and endogenous acceptors for sialylation. It seems likely that the primary defect in Lec2 and 1021 cells is their inability to translocate CMP-sialic acid across Golgi vesicle membranes.
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PMID:Translocation across Golgi vesicle membranes: a CHO glycosylation mutant deficient in CMP-sialic acid transport. 649 37

The translocation of adenosine 3'-phosphate 5'-phosphosulfate (PAPS) across rat liver Golgi-derived vesicles has been studied. Vesicles of the same topographical orientation as in vivo were incubated with a mixture of [adenine-8-3H]PAPS and [35S]PAPS. The tritium to radiolabeled sulfur ratio of the incubation medium was 1.73 +/- 0.03 while that in the vesicles was 1.82 +/- 0.13. This strongly suggests that the entire PAPS molecule was being translocated across the Golgi vesicle membrane even though intact PAPS could not be detected within the vesicles. Translocation of PAPS resulted in accumulation of solutes within vesicles. This accumulation was temperature dependent, saturable (apparent Km = 0.7 microM; Vmax = 25 pmol/mg of protein/10 min), and inhibited by the substrate analogue 3',5'-ADP but not by 2',5'-ADP. Translocation of PAPS was inhibited following treatment of Golgi vesicles with Pronase under conditions in which the activity of a lumenal Golgi membrane marker such as sialyltransferase was not. This result is consistent with the existence of a PAPS carrier protein, portions of which face the cytoplasmic side of the Golgi membrane.
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PMID:Translocation of adenosine 3'-phosphate 5'-phosphosulfate into rat liver Golgi vesicles. 670 70

During short incubations of a Golgi apparatus-enriched subcellular fraction from rat liver with UDP-[3H]GlcNAc, label is efficiently transferred to endogenous acceptors. Most of the macromolecular radioactivity is specifically released by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase, indicating that it is mainly associated with N-linked oligosaccharides. The glycoprotein acceptors are resistant to proteases unless detergent is added in amounts greater than the critical micellar concentration. This shows that the acceptors are within the lumen of intact compartments, which have the correct topological orientation expected for the Golgi apparatus in intact cells. Structural characterization of the radiolabeled N-linked oligosaccharides shows a variety of distinct neutral and anionic species. The neutral chains include bi-, tri-, and tetra-antennary molecules with terminal beta-[3H] GlcNAc residues. In vitro sialylation shows that some of the tetra-antennary chains have beta 1,3-linked Gal residues on their unlabeled antennae. An unknown modification appears to block the action of beta-galactosidase on these galactosylated oligosaccharides. Chasing the labeling reaction with a mixtures of UDP-Gal, CMP-Neu5Ac, and adenosine 3'-phosphate,5'-phosphosulfate causes an increase in the percent of radiolabeled anionic oligosaccharides. Most of the negative charge is due to sialic acid (Sia), and some appears to be in phosphodiester-linked [3H]GlcNAc. The sialylated oligosaccharides are a mixture of bi-, tri-, and tetra-antennary species with 1-3-Sia residues, and some of the [3H]GlcNAc residues are directly covered with unlabeled Gal and Sia residues. This in vitro approach should recapitulate reactions that occur in the biosynthesis of N-linked oligosaccharides in the Golgi apparatus of the intact cell. Since the conditions during labeling do not permit inter-compartmental transport, the oligosaccharides produced should represent the biosynthetic capabilities of individual Golgi compartments. Evidence is presented for a functional association of GlcNAc transferases I, II, and alpha-mannosidase II, with separation from GlcNAc transferase IV and/or V. The structures also indicate co-compartmentalization of several GlcNAc transferase(s) with beta-galactosyltransferase(s) and sialyltransferase(s). The compartmental organization of the Golgi apparatus is discussed in light of these findings.
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PMID:Biosynthesis of oligosaccharides in intact Golgi preparations from rat liver. Analysis of N-linked glycans labeled by UDP-[6-3H]N-acetylglucosamine. 834 99