title: Glucose-1-phosphotransferase and N-acetylglucosamine-1-phosphotransferase have distinct acceptor specificities.
abstract: UDP-glucose:glycoprotein glucose-1-phosphotransferase (Glc-phosphotransferase) catalyzes the transfer of alpha Glc-1-P from UDP-Glc to endoglycosidase H-sensitive oligosaccharides on acceptor glycoproteins. We have previously demonstrated that Glc-phosphotransferase was specific for UDP-Glc as its nucleotide sugar substrate and thus appeared to be distinct from UDP-N-acetylglucosamine:glycoprotein N-acetylglucosamine-1-phosphotransferase (GlcNAc-phosphotransferase), an enzyme specific for lysosomally destined acceptor glycoproteins. Here, sodium dodecyl sulfate-polyacrylamide gel electrophoresis autoradiographs of endogenous acceptor glycoproteins in embryonic chick neural retina homogenates labeled by the presence of [beta-32P]UDP-Glc were shown to be distinct from those labeled by [beta-32P]UDP-GlcNAc, indicating that the two enzymatic activities recognize different populations of endogenous glycoproteins. To further probe the acceptor specificities of these enzymes, three glycoproteins known to be exogenous acceptors for GlcNAc-phosphotransferase were included in assays for Glc-phosphotransferase from retinal homogenates. Cathepsin D and beta-N-acetylhexosaminidase had no significant effects on phosphoglucose incorporation. Uteroferrin, an acid phosphatase, had a pronounced inhibitory effect on incorporation from UDP-Glc, and subsequent experiments suggested that phosphorylation of the Glc-phosphotransferase or another protein may be necessary for maximal activity to be seen. Also, I-cells, which have previously been shown to possess no GlcNAc-phosphotransferase activity, and control human fibroblasts were assayed for both Glc-phosphotransferase and GlcNAc-phosphotransferase. GlcNAc-phosphotransferase activity was observed only in control cells, whereas Glc-phosphotransferase was observed in both I-cells and controls at similar specific activities.
mesh_terms: D000135:Acid Phosphatase; D000818:Animals; D002402:Cathepsin D / Q000494:pharmacology; D002642:Chick Embryo; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000201:enzymology; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes; D008667:Metalloproteins / Q000494:pharmacology; D009081:Mucolipidoses / Q000201:enzymology; D010047:Ovalbumin / Q000494:pharmacology; D010770:Phosphotransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012160:Retina / Q000201:enzymology; D013379:Substrate Specificity; D000071681:Tartrate-Resistant Acid Phosphatase; D017855:Transferases (Other Substituted Phosphate Groups); D014532:Uridine Diphosphate Glucose / Q000378:metabolism; D014537:Uridine Diphosphate N-Acetylglucosamine / Q000378:metabolism; D001619:beta-N-Acetylhexosaminidases / Q000494:pharmacology
chemical_list: D006023:Glycoproteins; D007527:Isoenzymes; D008667:Metalloproteins; D014537:Uridine Diphosphate N-Acetylglucosamine; D010047:Ovalbumin; D010770:Phosphotransferases; D017855:Transferases (Other Substituted Phosphate Groups); C023222:UDPacetylglucosamine-dolichyl-phosphate acetylglucosamine-1-phosphate transferase; C037061:UDPglucose-glycoprotein glucose-1-phosphotransferase; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase; D001619:beta-N-Acetylhexosaminidases; D002402:Cathepsin D; D014532:Uridine Diphosphate Glucose