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

Abstract

Phospholipase A activities in plasma membranes (PMs), isolated from rat ascites hepatoma cells (AH 130, AH 130FN, 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 phospholipase A₂ activity was detected equally but with a specific activity higher than that of phospholipase 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, Al and A₂, activities of the hepatoma PMs.