THE DIFFERENTIATION OF PHOSPHOLIPASE A1 AND A2 IN RAT AND HUMAN NERVOUS TISSUES

Abstract —Lipid‐free extracts of rat and human brain have been prepared and shown to contain phospholipase A1 and A2 activities and a lysophospholipase. The phospholipase Aj activity has pH optima of 4·2 and 4·6 in rat and human brain, respectively; it can be partially purified and isolated in high yields by dialysing the extracts at low pH. The purified preparations hydrolyse the ester bond at the 1‐position in lecithin, phosphatidyl‐ethanolamine and phosphatidylserine, but have little or no action on triglyceride or cholesterol ester. An assay system for the enzyme is described. Phospholipase A2 activity is optimal at pH 5·5 in rat brain extracts and at pH 5·0 in extracts of human brain. The phospholipase A2 activity of human cerebral cortex is largely unaffected by heating extracts at 70°C for 5 min, whereas this treatment substantially inactivates phospholipase A1 and completely destroys lysophospholipase. Phospholipase A1 is widely distributed in both grey and white matter of human brain and is also present in peripheral nerve. Phospholipase A2 activity is lower than A1 in all regions of the CNS examined so far, and is absent from peripheral nerve. Neither enzyme appears to require Ca2+ but both are inhibited by di‐isopropylfluorophosphate (DFP, 2 × 10−6 m) and thus differ from phospholipase A of pancreas. These studies confirm that the phospholipase A1 and A2 activities in brain are due to separate enzymes.