Autophosphorylation of the purified human insulin receptor tyrosyl kinase was found to be inhibited by the ras oncogene product p21 in a concentration- and GDP-dependent manner. GDP-β-S but not Gpp(NH)p could substitute for GDP in eliciting the ras-dependent inhibition. The inhibition was seen with both normal or mutant (Lys-61) p21N-ras and normal or mutant (Val-12) p21Ha-ras. Inhibition occurred at 23°C but not 4°C and was unaffected by the presence or absence of insulin although insulin stimulated the autophosphorylation rate of the receptor β-subunit some 2-fold. The insulin receptor did not phosphorylate native p21Ha-ras in the presence or absence of added guanine nucleotide. After denaturation of p21Ha-ras with urea it became a substrate, but then failed to inhibit receptor autophosphorylation even in the presence of added GDP.
