| Abstract: | An increase in glycogen synthase phosphatase (phosphoprotein phosphatase) activity was observed in the rat skeletal muscle extract following insulin administration. The phosphoprotein phosphatase activity present in the muscle extract from insulin treated rats was observed to remain elevated after the extract had been subjected to a molecular sieve chromatography. These results indicate that the stimulatory effects of insulin is due to modification of phosphatase itself or some macromolecular weight modifiers. The heat-stable protein inhibitors of the phosphoprotein phosphatase were isolated from skeletal muscle of insulin treated and control rats and their inhibitory potencies were compared over a wide range of protein concentrations. The inhibitory potency in the insulin treated rat skeletal muscle was found to be significantly less than that in the control muscle. Since type-1 inhibitor is well-known to be active only after being phosphorylated by cyclic AMP-dependent protein kinase, we suggest that the observed change in phosphoprotein phosphatase inhibitor potency is most likely mediated by an alteration in the phosphorylation state of type-1 inhibitor. |
