Factors affecting the activity of muscle glycogen synthetase: III. The reaction with adenosine triphosphate, Mg ++, and cyclic 3′5′-adenosine monophosphate

Abstract

The in vitro conversion of rat muscle glycogen synthetase from the I form to the less active D form in a reaction requiring ATP and Mg ++ has been investigated. The stimulation of this reaction by cyclic 3′5′-AMP has been measured and a comparison of the nucleotide requirements to those in the activation of muscle phosphorylase b kinase has been made. An inhibitor of the I to D conversion of glycogen synthetase has been compared with a similar factor from muscle extracts which affects phosphorylase b kinase activation. The results are discussed in the light of current hypotheses on the mechanisms of action of epinephrine and insulin.