Inactivation of Na+-K+-Dependent ATPase by Phospholipase-treatment and Its Reactivation by Phospholipids*

Abstract

1. An Na⁺-K⁺-dependent ATPase [EC 3. 6. 1. 3] preparation from ox brain microsomes was treated with Naja naja venom or phospholipase C [EC 3. 1. 4. 3]. About 70% of phospholipids in the preparation were changed to lyso-compounds by treatment with venom, while the content of phospholipids was reduced to about 40% by treatment with phospholipase C. 2. The Na⁺-K⁺-ATPase activity was reduced to 5–25% and to 40% of the control value, by treatment with Naja naja venom and phospholipase C, respectively. The residual ATPase activity after treatment with phospholipase, like that of the control, was dependent on Na⁺ and K⁺ and sensitive to Ouabain. 3. After the preparation had been treated with Naja naja venom in 2.95 M Na-acetate, its ATPase activity was reactivated to 50% of the control value by addition of PI. It was further reactivated to the control level by addition of PI+PS or PI+PS+PE. After treatment with venom in the presence of B.S.A., the ATPase activity was reactivated to 75% of the control value by addition of PI or PS. It was further reactivated to 90% of the control by addition of both PI and PS. The ATPase activity after treatment with phospholipase C was reactivated to 85% of the control value by addition of PS. 4. Treatment with venom reduced the rate of EP formation by about 60%, and reduced the rate of EP decomposition by more than 90%. The rates of EP formation and decomposition were increased to the control level and to 40% of the control level, respectively, by addition of PI+PS.