Enhanced Degradation of Phospholipids by Phospholipase A2 in Liver of Carbon Tetrachloride-Treated Rat

Abstract

Stimulated phospholipid degradation was observed in liver homogenates harvested from rats who had received an injection of carbon tetrachloride (CCl₄). When the liver homogenates obtained from CCl₄-treated rats were incubated for 1 h at 37°C, approximately half of the phosphatidylethanolamine (PE) was hydrolyzed, producing a stoichiometrical amount of lysophosphatidylethanolamine (LysoPE). The homogenates obtained from control rats showed only poor hydrolytic activity toward endogenous PE. The fatty acid composition of lysoPE produced was essentially identical to that at the sn-1 position of PE, suggesting that A₂ type of phospholipase (PLase A₂) was involved in the degradation during incubation. The hydrolysis of endogenous PE was dependent on calcium ion. The hydrolytic activity was almost exclusively associated with the membrane fraction which was precipitated by centrifugation at 10000 × g, and did not require the cytosol fraction. Para-bromophenacylbromide, rabbit antibody against rat 14 kDa type II PLase A₂, and thielocin A₁, a specific inhibitor of type II PLase A₂, suppressed the hydrolysis almost completely. These results indicate that the accelerated degradation of endogenous PE observed in liver homogenates of CCl₄-treated rat may be mainly due to the activity of the enzyme closely related to type II PLase A₂.