Insulin action in intact mouse diaphragm. II. Inhibition of endogenous protein phosphorylation.

Incubation of intact mouse diaphragms with insulin in the absence of glucose resulted in a rapid inhibition of the subsequent cell-free phosphorylation of endogenous protein substrates in tissue extracts. The phosphorylation of added histone was inhibited to a lesser extent. The inhibition was observed both in the absence and in the presence of added cyclic 3'5' adenosine monophosphate. Acrylamide gel electrophoresis of phosphorylation products revealed a number of major phosphorylated polypeptides. The phosphorylation of several polypeptides was inhibited following short treatment with insulin. These results represent a novel experimental approach to the elucidation of the mechanism of the action of insulin and are consistent with our hypothesis that the inhibition of protein kinase activities in the tissue may be the first step in this mechanism.