A phospho-oligosaccharide mimics the effect of insulin to inhibit isoproterenol-dependent phosphorylation of phospholipid methyltransferase in isolated adipocytes.
Addition of isoproterenol to isolated rat adipocytes prelabeled with [32P]phosphate caused an increase in the phosphorylation and activation of phospholipid methyltransferase. 32P-Labeled phospholipid methyltransferase was recovered by immunoprecipitation and gel electrophoresis. Analysis of 32P-labeled peptides revealed one site of phosphorylation regulated by isoproterenol, and analysis of phosphoamino acids demonstrated that the incorporation of [32P]phosphate was on phosphoserine. Incubation of adipocytes with isoproterenol in the presence of insulin or a phospho-oligosaccharide inhibited the phosphorylation and activation of this enzyme. The inhibitory effect of insulin on the phosphorylation of phospholipid methyltransferase was reversible, and it was mimicked by a phospho-oligosaccharide. The phospho-oligosaccharide was generated by hydrolysis of an isolated glycophospholipid with phosphatidylinositol-specific phospholipase C from Staphylococcus aureus. The insulin-like effect of this phospho-oligosaccharide on the phosphorylation of phospholipid methyltransferase was demonstrated in isolated adipocytes, and the effect was abolished by treatment of the phospho-oligosaccharide with 10% NH4OH, nitrous acid, or sodium periodate. These data suggest that in intact adipocytes the effect of insulin to inhibit the phosphorylation/activation of phospholipid methyltransferase is mediated by a phospho-oligosaccharide generated by a phosphatidylinositol-specific phospholipase C.
Kelly
K L
KL
Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104.
Merida
I
I
Wong
E H
EH
DiCenzo
D
D
Mato
J M
JM
D000273:Adipose Tissue / Q000187:drug effects / Q000201:enzymology*; D000818:Animals; D004789:Enzyme Activation; D006017:Glycolipids / Q000302:isolation & purification / Q000502:physiology*; D066298:In Vitro Techniques; D007328:Insulin / Q000494:pharmacology*; D007545:Isoproterenol / Q000494:pharmacology*; D008099:Liver / Q000502:physiology; D008297:Male; D008780:Methyltransferases / Q000378:metabolism*; D008970:Molecular Weight; D009844:Oligosaccharides / Q000502:physiology*; D050941:Phosphatidyl-N-Methylethanolamine N-Methyltransferase; D050918:Phosphatidylethanolamine N-Methyltransferase; D010743:Phospholipids / Q000302:isolation & purification / Q000502:physiology*; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000201:enzymology
D006017:Glycolipids; D007328:Insulin; D009844:Oligosaccharides; D010743:Phospholipids; D008780:Methyltransferases; D050918:Phosphatidylethanolamine N-Methyltransferase; D050941:Phosphatidyl-N-Methylethanolamine N-Methyltransferase; D007545:Isoproterenol