Coordinated feedback regulation of muscle glycogen metabolism: inhibition of purified phosphorylase phosphatase by glycogen.

An assay method was devised for accurately measuring the activity of phosphorylase phosphatase in the presence of glycogen. Both oyster glycogen and rabbit liver glycogen inhibited the activity of purified phosphorylase phosphatase catalytic subunit in a concentration-dependent manner. In the presence of 120 mM KCl, micromolar AMP increased the sensitivity of the phosphatase to glycogen inhibition. The present studies suggest that glycogen feedback inhibition may be a coordinated mechanism producing a decrease in phosphorylase phosphatase activity as well as glycogen synthase phosphatase activity.