GENERATION BY INSULIN OF A CHEMICAL MEDIATOR THAT CONTROLS PROTEIN-PHOSPHORYLATION AND DEPHOSPHORYLATION

Deproteinized skeletal muscle extracts free of major nudeotides from control and insulin-treated rats were fractionated and assayed for inhibition of protein phosphorylation by cyclic adenosine monophosphate (AMP)-dependent and -independent protein kinases. A differential effect of insulin on a particular fraction was observed on cyclic AMP-dependent protein kinase but not on cyclic AMP-independent protein kinases. This fraction that inhibited cyclic AMP-dependent protein kinase also stimulated glycogen synthase phosphoprotein phosphatase. It is proposed that this fraction may contain mediator substance generated in the presence of insulin.