Phosphohistone and glycogen synthase D phosphatase activities in a liver glycogen pellet preparation.

A liver glycogen pellet preparation previously found to contain synthase D phosphatase activity was shown to contain also phosphohistone phosphatase activity. Pellet phosphohistone phosphatase and synthase D phosphatase competed for the same substrates and appeared to be the same enzyme. ATP, a potent inhibitor, and G-6-P, a potent activator of the synthase phosphatase reaction, had little effect on the phosphohistone phosphatase reaction. These observations suggest that the ATP and G-6-P effects are relatively specific and are probably caused by binding to the synthase D substrate. The observed effects of NaCl and KCl were more complex. They stimulated phosphohistone phosphatase activity but strikingly inhibited synthase phosphatase activity. Sodium fluoride inhibited both reactions.