Presence of an insulin-stimulated serine kinase in cell extracts from IM-9 cells.

Insulin responsive protein kinase activities of wheat germ purified glycoproteins were examined. Glycoproteins were first incubated without or with insulin, and then exposed to a serum containing antibodies to insulin receptor. Thereafter, both immunoprecipitates and supernatants were studied for their kinase activity toward histone. Incubation with anti receptor antibodies promoted insulin receptor beta subunit and histone phosphorylation. More important insulin receptor depleted extract contained a kinase activity toward histone, that was increased by preincubation with insulin. This stimulation was observed only when insulin was added before the immunoprecipitation of insulin receptors. Alkali treatment and phosphoamino acids analysis revealed that the kinase activity remaining in the supernatant is serine specific. These findings suggest, that a serine kinase activity is associated with the insulin receptor, that it can be separated from the insulin receptor with anti receptor antibodies, that the serine kinase is activated by the hormone-receptor complex.