Phosphatidic Acid Metabolism in Rat Liver Microsomes

Abstract

Rat liver microsomes contain phosphatidate phosphatases which split phosphatidic acid into inorganic phosphate and diacylglycerol and a system of phospholipases and lipases, which split phosphatidic acid into free fatty acids, glycerol and inorganic phosphate. In the presence of ATP, CoA and [1‐¹⁴C]palmitate, part of the monoacyl‐sn‐glycerol 3‐phosphate formed by phospholipase action is reesterified, yielding radioactive phosphatidic acid. The sum of di‐ and triacylglycerols formed from phosphatidic acid in the presence of ATP and CoA exceeded the amount of diacylglycerol fromed in their absence. The yield of neutral lipids from sn‐glycerol 3‐phosphate and monoacyl‐sn‐glycerol 3‐phosphate markedly exceeded that from phosphatidic acid. Comparison of the yields of di‐ and triacylglycerols from glycerol‐labelled and fatty‐acid‐labelled phosphatidic acid was used to establish the extent of deacylation and reacylation. About 60% of the diacylglycerol was formed by direct dephosphorylation. The triacylglycerols, on the other hand, were formed almost exclusively from recycled phosphatidic acid.