The enzymic release of fatty acids from phosphatidylcholine in green peas (Pisum sativum)

‘Phospholipid acyl-hydrolase’ (PLAH), an enzymic activity releasing fatty acid from phosphatidylcholine (PC), has been identified and characterised in green peas. The K_m value for PC dipalmitoyl ester was 0·167 mm. The enzymic activity possessed a pH optimum of 5·6 and was stable for 20 min only at that pH value. The optimum temperature was 45°C and thermal sensitivity was indicated by a 94% decrease in activity upon exposure of the enzyme to 55°C for 3 min, and by an exponential decrease in activity upon storage at 4°C for 1 week. The enzyme was optimally activated by 2·0 mm calcium chloride at pH 5·6, and the optimal concentration of sodium dodecyl sulphate was 0·75 mg ml^?1. Pea PLAH was non-competitively inhibited by sodium cyanide, EDTA and p-chloromercuribenzoate, with no activity in the presence of mercuric chloride. The results from this study are related to those of other workers on lipid-degrading enzymes in peas, and a pathway is proposed for the enzymic degradation of endogenous lipids in fresh or unblanched frozen peas during post-harvest storage.