Early changes of protein-kinase (glycogen-synthetase kinase) in denervated muscle

Abstract

After denervation, muscle glycogen decreases in simultaneously with glycogen synthetase I activity (the physiologically active form of this enzyme). The present experiment was performed to determine the changes, if any, in the enzymes that convert glycogen synthetase from the inactive D form to the active I (glycogen synthetase phosphatase) as well as the opposite reaction (glycogen synthetase kinase or protein kinase). Enzyme activities were assayed by testing the capability of muscle extracts to cause conversion of purified glycogen synthetase D (in the case of phosphatase determinations) or of purified glycogen synthetase I (kinase assays) in the presence of the required cofactors and activators. No changes of glycogensynthetase phosphatase were observed. However, there was a marked increase of both the cAMP independent and the total kinase activities 1 day after denervation. This fact can account for the changes in glycogen synthetase I levels and in glycogen metabolism after denervation. Also, it might be relevant to understand the early changes in RNA and protein metabolism after denervation, owing to the supposed regulatory effect of protein kinase on nuclear activity.