Calmodulin ligands. The interaction of muscle phosphorylase kinase with phosphodiesterase. Comparison of calmodulin ligands in muscle extracts from normal and phosphorylase kinase-deficient mice.

Interactions between phosphorylase kinase (ATP:phosphorylase-b phosphotransferase, EC 2.7.1.38) and calmodulin were studied with pure preparations of muscle phosphorylase kinase, and with crude extracts from muscles of control (C57 Black) and deficient (ICR/IAn) mice, which lack muscle phosphorylase kinase activity. Calmodulin was determined by its ability to stimulate a calmodulin-dependent phosphodiesterase. The amount of calmodulin bound to phosphorylase kinase in muscle extract was estimated to a maximum of 30% of the total amount of calmodulin. In the muscle of the deficient strain a decrease of 35% in the total amount of calmodulin was observed. This correlates with the absence of the calmodulin fraction specifically bound to phosphorylase kinase. From sucrose gradient studies we demonstrated that in the presence of Ca2+ the amount of calmodulin bound to phosphorylase kinase was enhanced, compared to the control in the presence of EGTA. This observation was made both in crude extracts and in pure phosphorylase kinase preparations. Sucrose gradient also showed that muscle phosphorylase kinase can be dissociated to low molecular species when extracts are made in the presence of Ca+; this dissociation was found to be related to a Ca2+-dependent proteolytic effect.