Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.11 (AMPK)
 12,425 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have investigated the possible role of a cAMP-mediated protein-phosphorylation event(s) as the key regulatory mechanism in beta-adrenoreceptor-stimulated activation of mannosylphosphodolichol (Man-P-Dol) synthase (GDP-mannose:dolichyl-phosphate O-beta-D-mannosyltransferase, EC 2.4.1.83) in rat parotid acinar cells. Microsomal membranes isolated from these cells pretreated with 10 microM isoproterenol for 60 min showed approximately 40-80% enhanced Man-P-Dol synthase activity compared to the untreated controls. This change in enzyme activity was not associated with a significant alteration in apparent Km for GDP-mannose, but the Vmax was enhanced 2-fold. When microsomal membranes isolated from control cells were phosphorylated in vitro by a cAMP-dependent protein kinase, an increase in Man-P-Dol synthase activity, similar to that with membranes from isoproterenol-treated cells, was observed (i.e., a moderate change in Km for GDP-mannose but a 2-fold higher Vmax). Furthermore, treatment of in vitro phosphorylated microsomal membranes by alkaline phosphatase led to a substantial reduction in Man-P-Dol synthase activity. Increased Man-P-Dol synthesis (approximately 30-40%) was also observed in bovine brain and hen oviduct microsomal membranes after in vitro protein phosphorylation. In aggregate, these results strongly suggest that agents that increase cAMP in cells may modulate protein N-glycosylation in those cells by activating this key glycosyltransferase of the dolichol cascade by a cAMP-dependent protein kinase-mediated protein phosphorylation/dephosphorylation cycle.
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PMID:cAMP-mediated protein phosphorylation of microsomal membranes increases mannosylphosphodolichol synthase activity. 281 74

Dolichol phosphate mannose synthase, an essential enzyme in glycoprotein biosynthesis, was partially purified from E.histolytica by hydrophobic interaction and affinity chromatography with octyl Sepharose CL-4B and Affi-Gel 501, respectively. Reducing agents, particularly dithiothreitol, positively influenced enzyme activity and stability, indicating a role of sulfhydryl groups on the transferase function. Activity did not depend on phospholipids; however, it was significantly stimulated by phosphatidylethanolamine and to a lower extent by other common phospholipids. Mixtures consisting of activating phospholipids did not exert an additive effect. In vitro phosphorylation with a cAMP-dependent protein kinase resulted in enzyme activation. This alteration was not associated with a change in the K(m) for the substrate but rather with a 2.6-fold increase in V(max). Phosphorylation in the presence of [gamma-(32)P]ATP resulted in strong labeling of two polypeptides, one of which exhibited the molecular mass reported for the enzyme from other organisms. Whether phosphorylation functions in vivo as a mechanism of regulation of dolichol phosphate mannose synthesis in E.histolytica remains to be determined.
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PMID:Partial purification and characterization of dolichol phosphate mannose synthase from Entamoeba histolytica. 1115 22