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