Occurrence and Properties of Phospholipases A1 of Plasma Membranes Prepared from Neuronal- and Glial-Enriched Fractions of the Rabbit Cerebral Cortex

Abstract: Exogenously added glycerophosphatides, specifically radioactively labelled either in the 1 or in the 2 position, were used to investigate the occurrence and properties of phospholipase A₁ in plasma membranes prepared from neuronal- and glial-enriched fractions of rabbit brain. Phospholipase A₁ activity was maximal at pH values ranging between 8.0 and 9.0 for the plasma membranes of both cell types. The enzyme activity was most abundant in the microsomal fraction, with a neurondglial ratio of about 2. The plasma membranes displayed about half the enzymic activity of the microsomal fraction, whereas only small amounts of phospholipase A₁ were present in the neuronal and glial mitochondria. Investigations on the substrate specificity showed a different pattern for the enzyme of neuronal and glial origin. The release of labelled fatty acids from phosphatidylcholine by the neuronal plasma membrane phospholipase A₁ decreased with increasing degree of unsaturation of the fatty acids at the 1 position. The presence of plasmalogens and plasmalogen precursors in the incubation mixture appreciably inhibited the hydrolysis of the corresponding diacyl compounds.