ADENOSINE 3',5'-CYCLIC MONOPHOSPHATE-DEPENDENT PROTEIN-KINASE (A KINASE) REGULATION OF INSULIN-RECEPTOR FUNCTION - PHOSPHORYLATION OF INSULIN-RECEPTOR WITH A-KINASE DECREASES THE INSULIN BINDING-ACTIVITY

The effect of phosphorylation of insulin receptor with adenosine 3', 5'-cyclic monophosphate-dependent protein kinase (A kinase) on its insulin binding activity was investigated by using insulin receptors prepared from rat liver in vitro. A 95 KDa protein was phosphorylated by stimulation of insulin receptor kinase. This protein was also phosphorylated by A kinase. Analysis of phosphoamino acid showed that tyrosine residue(s) was phosphorylated by activation of insulin receptor kinase, whereas phosphoserine and phosphothreonine were dominantly generated by activation of A kinase. [I-125] Iodoinsulin binding activity was decreased by prior phosphorylation of the receptor with A kinase. Scatchard analysis showed that the affinity for insulin was decreased by the phosphorylation with A kinase. Although the maximal activity of insulin receptor kinase was not affected by phosphorylation with A kinase, the insulin concentration which induced half maximal activity (ED50) of the receptor kinase was increased by the phosphorylation with A kinase. These results suggested that counter regulatory hormones whose actions are mediated by the generation of adenosine 3', 5'-cyclic monophosphate regulate the insulin binding to the alpha-subunit through phosphorylation of the beta-subunit of insulin receptor.