Phospholipid Requirements of Ca++-Stimulated, Mg++-Dependent ATP Hydrolysis in Rat Brain Synaptic Membranes

摘要

The phospholipid requirement for calcium ion-stimulated, magnesium ion -dependent (ATP) hydrolysis(Ca (++) /Mg (++)-ATPase) and Mg(++) -stimulated ATP hydrolysis (Mg(++)-ATPase) in rat brain synaptosomal membranes was studied employing partial delipidation of the membranes with phospholipase A2 (hog pancreas), phospholipase C (Bacillus Cereus), and phospholipase D (cabbage). Treatment with phospholipase A2 caused an increase in the activities of Ca(++)-ATPase, but Mg(++)-ATPase activity was inhibited. Inhibition of Mg(++) -ATPase activity after phospholipase C treatment was relieved with the addition of phosphatidylinositol-4, 5-biphosphate (PIP2) and to a lesser extent with phosphatidylinositol-4-phosphate (PIP) and phosphatidylcholine (PC). Phosphatidylserine (PS), phosphatidic acid (PA), PIP, and PIP2 brought about the reactivation of Ca(++)/Mg (++) ATPase activity. The Michaelis constants (Kms) for Ca(++) (0.47 micromoles) and Mg(++) (60 micromoles) of the enzyme was unaffected after treatment with the phospholipases. (aw)