PURIFICATION OF A HIGH-MOLECULAR-MASS FORM OF PHOSPHOLIPASE-A2 FROM RAT-KIDNEY ACTIVATED AT PHYSIOLOGICAL CALCIUM CONCENTRATIONS

Rat kidney contains a soluble phospholipase A2 (PLA2), which is chromatographically identical with a previously identified hormonally regulated form of the enzyme in rat renal mesangial cells. This kidney enzyme has been purified by sequential column fractionation. The purified enzyme is a 110 kDa polypeptide which can hydrolyse arachidonoyl phosphatidylcholine and arachidonoyl phosphatidylethanolamine, but has low activity towards arachidonoyl phosphatidylinositol. The enzyme is considerably larger than most previously isolated forms of secretory or intracellular PLA2, and is stimulated by physiological concentrations of Ca2+, with half-maximal activation occurring at 500 nM-Ca2+. The hormonal regulation and Ca2+-dependency of this enzyme strongly suggest that it plays a role in hormonally regulated arachidonic acid release and prostaglandin production in the kidney.