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

Abstract

Abstract —Lipid‐free extracts of rat and human brain have been prepared and shown to contain phospholipase A 1 and A 2 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 A 2 activity is optimal at pH 5·5 in rat brain extracts and at pH 5·0 in extracts of human brain. The phospholipase A 2 activity of human cerebral cortex is largely unaffected by heating extracts at 70°C for 5 min, whereas this treatment substantially inactivates phospholipase A 1 and completely destroys lysophospholipase. Phospholipase A 1 is widely distributed in both grey and white matter of human brain and is also present in peripheral nerve. Phospholipase A 2 activity is lower than A 1 in all regions of the CNS examined so far, and is absent from peripheral nerve. Neither enzyme appears to require Ca 2+ 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 A 1 and A 2 activities in brain are due to separate enzymes.