Phospholipid requirement of Ca2+-stimulated,Mg2+-dependent ATP hydrolysis in rat brain synaptic membranes |
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Authors: | C. R. Gandhi D. H. Ross Ph.D. |
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Affiliation: | (1) Division of Molecular Pharmacology Department of Pharmacology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, 78284 San Antonio, Texas |
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Abstract: | The phospholipid requirement for Ca2+-stimulated, Mg2+-dependent ATP hydrolysis (Ca2+/Mg2+-ATPase) and Mg2+-stimulated ATP hydrolysis (Mg2+-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 both Ca2+/Mg2+-ATPase and Mg2+-ATPase whereas with phospholipase C treatment both the enzyme activities were inhibited. Phospholipase D treatment had no effect on Ca2+/Mg2+-ATPase but Mg2+-ATPase activity was inhibited. Inhibition of Mg2+-ATPase activity after phospholipase C treatment was relieved with the addition of phosphatidylinositol-4,5-bisphosphate (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 Ca2+/Mg2+-ATPase. Phosphatidylinositol (PI) and PA inhibited Mg2+-ATPase activity.Kms for Ca2+ (0.47 M) and Mg2+ (60 M) of the enzyme were found to be unaffected after treatment with the phospholipases. |
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