The Effect of Phospholipase A on the Calcium Transport and the Role of Unsaturated Fatty Acids in ATPase Activity of Sarcoplasmic Vesicles

Abstract

1 The cleavage of the β-ester bond of the phospholipids in the membranes of the sarcoplasmic reticulum by phospholipase A increases the permeability of the membranes for calcium whereby the ATP driven calcium storage is abolished. The activity of the calcium dependent ATPase remains unimpaired. The splitting products of the phospholipids which are composed of unsaturated fatty acids and prevailingly saturated lysolecithins are firmly attached to the membranal protein. They are removed from the protein by bovine serum albumin. The calcium dependent ATPase activity and the phosphoryl-transfer from ATP to the membranal protein are abolished thereby. 2 Unsaturated fatty acids restore the phosphoryl transfer reaction and the calcium dependent ATPase. Lysolecithin restores the ATPase activity nearly to the same extent but the phosphoryl transfer reaction is not reactivated. The accumulation of calcium is not restored either by unsaturated fatty acids or lysolecithin. 3 The calcium dependent ATPase reactivated by fatty acids is more sensitive towards prenylamine than the ATPase reactivated by lysolecithin. Prenylamine is bound to the vesicles activated by fatty acids whereas the vesicles reactivated with lysolecithin do not bind the drug.