title: Protein kinase C directly phosphorylates the insulin receptor in vitro and reduces its protein-tyrosine kinase activity.
abstract: The beta subunit of purified insulin receptor is phosphorylated on a serine residue by purified preparations of protein kinase C (ATP: protein phosphotransferase, EC 2.7.1.37). This phosphorylation is inhibited by antibodies to protein kinase C and stimulated by phospholipids, diacylglycerol, and Ca2+. The phosphorylation of the receptor by protein kinase C does not affect its insulin-binding activity but does inhibit by 65% the receptor's intrinsic tyrosine-specific protein kinase activity (ATP: protein-tyrosine O-phosphotransferase, EC 2.7.1.112). These results indicate that activators of protein kinase C, such as phorbol esters, desensitize cells to insulin by direct protein kinase C action on the insulin receptor.
mesh_terms: D000818:Animals; D004789:Enzyme Activation; D007328:Insulin / Q000031:analogs & derivatives / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011972:Receptor, Insulin / Q000378:metabolism*
chemical_list: D007328:Insulin; D046911:Macromolecular Substances; C008147:insulin, iodo-; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin; D011493:Protein Kinase C