Liver glycogen synthase phosphatase and phosphorylase phosphatase activities in vitro following glucose and glucagon administration

Correlation of the changes in phosphorylase a concentration with the synthase phosphatase velocity in a glycogen particle preparation in the presence of EDTA revealed that the initial synthase phosphatase rate was greatest in extracts from glucose-treated rats and least in extracts from glucagon-treated rats. In all cases the velocity increased with time and with a decrease in phosphorylase a. However, a threshold release of phosphatase activity when phosphorylase a reached a critical level was not observed. The data are compatible with either an independent regulation of synthase phosphatase by glucose and glucagon or regulation of the activity by phosphorylase over a range of phosphorylase a concentrations.