Inhibition of liver glycogen synthase phosphatase by calcium new evidence for an interaction between synthase activation and phosphorylase a

Abstract

In mouseliver gel filtrates incubated at 20°C in the presence of 0.5 % glycogen, 50 mM glycylglycine pH 7.4 and 5 mM (NH4) 2SO4, the activation of glycogen synthase occurred only after a lag period corresponding to the time required to convert phosphorylase a to the b form; this activation of synthase in the absence of phosphorylase a was enhanced by about 30 % in the presence of 3 mM EGTA alone and was maximally inhibited (about 30 %) in the presence of 10−7M Ca++. Under other experimental conditions the activation of synthase was already apparent in the presence of phosphorylase a and proceeded without latency, but became sensitive to Ca++ only after the disappearance of phosphorylase a. Phosphorylase inactivation was unaffected by EGTA or Ca++ in the 10−5-10−8M range in any of the experimental conditions.