Phospholipase A in the Plasma Membranes of Ascites Hepatomas and of Normal Livers in Rat 1

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Abstract
Phospholipase A activities in plasma membranes (PMs), isolated from rat ascites hepatoma cells (AH 130, AH 13OFN, AH 7974, and AH 7974F), were determined and compared with those in PMs isolated from normal rat livers (neonatal, resting adult, and regenerating adult livers). All the PMs had a hydrolyzing action on 1-acyl-2-[14C]oleyl-sn-glycero-3-phosphoethanolamine but not on similarly labeled phosphatidylcholine. After hydrolysis, the radioactivity was recovered in both the lyso derivative and the free fatty acid produced. Thus, the presence of phospholipases A1 and A2 in the PMs, with an optimal pH around pH 9, was demonstrated. In all the hepatoma PMs, the phospholipase A2 activity was greatly reduced or almost lacking, whereas in the PMs from normal resting and growing livers strong phos pholipase A2 activity was detected equally but with a specific activity higher than that of phos pholipase A1. Triton X-100 treatment had an activating effect on phospholipase A1 but an inhibitory effect on phospholipase A2 of the resting liver PMs, while the same treatment was inhibitory for both the phospholipase, A1 and A2 activities of the hepatoma PMs.