Regulation of cardiac insulin receptor function by guanosine nucleotides

The present study examined the effect of GTP-gamma-S on the function of insulin receptors partially purified from adult rat cardiomyocytes by WGA chromatography. GTP-gamma-S increased receptor autophosphorylation about two times and fully mimicked the stimulatory action of insulin on poly(Glu:Tyr) phosphorylation with no additional effect of the hormone. The effect of GTP-gamma-S was specific, dose-dependent, and due to an increase in the Vmax of the kinase. In the presence of ATP or AMP-PNP, insulin significantly enhanced the binding of [35S]GTP-gamma-S to the partially purified insulin receptor. The findings suggest coupling of the insulin receptor to a G-protein which may be involved in the regulation of tyrosine kinase activity.