The insulin receptor tyrosyl kinase phosphorylates holomeric forms of the guanine nucleotide regulatory proteins Gi and Go

Abstract

An affinity purified human insulin receptor preparation was shown to phosphorylate the α- and β-subunits of the guanine nucleotide-regulatory proteins G_i and G_o, derived from bovine brain. The presence of insulin stimulated the rate of their phosphorylation some 2-fold. The presence of G_i and G_o did not affect the degree of autophosphorylation of the β-subunit of the insulin receptor. Under conditions known to cause the dissociation of G_i and G_o into their constituent subunits then phosphorylation of G_i and G_o by the insulin receptor was abolished. The α-subunits of G_i and G_o could be selectively phosphorylated by the insulin receptor tyrosyl-kinase using appropriate concentrations of Mg²⁺ and GTP-γ-S.