ATPase and phosphatase activities from human red cell membranes: II. The effects of phospholipases on Ca2+-dependent enzymic activities

Summary Treatment of human red cell membranes with pure phospholipase A₂ results in a progressive inactivation of both Ca²⁺-dependent and (Ca²⁺+K⁺)-dependent ATPase and phosphatase activities. When phospholipase C replaces phospholipase A₂, Ca²⁺-dependent ATPase activity and Ca²⁺-dependent phosphorylation of red cell membranes are lost, while Ca²⁺-dependent phosphatase activity is enhanced and its apparent affinity for Ca²⁺ is increased about 20-fold. Activation of Ca²⁺-dependent phosphatase following phospholipase C treatment was not observed in sarcoplasmic reticulum preparation. Phospholipase C increases the sensitivity of the phosphatase to N-ethylmaleimide but has little effect on the kinetic parameters relating the phosphatase activity to substrate and cofactors, suggesting that no extensive structural disarrangement of the Ca²⁺-ATPase system has occurred after incubation with phospholipase C.