Calcium-stimulated, ATP-magnesium-dependent inactivation of pig liver glycogen synthase

Ca2+-stimulated inactivation of liver glycogen synthase was observed when a partially purified liver phosphorylase kinase fraction containing glycogen synthase was incubated with ATP-Mg2+. The Ca2+-stimulated portion of this inactivation was partially counteracted by trifluoperazine and slightly stimulated by exogenously added calmodulin. These results suggest that Ca2+-calmodulin may be involved as one of the factors causing this glycogen synthase inactivation. Although the exact mechanism mediated by Ca2+ has not been clearly determined, the possibility of the participation of some Ca2+-dependent protein kinase is discussed.