Solubilization and characterization of a neutral-active, calcium-dependent, phospholipase A2 from rabbit heart and...

Homogenates of rabbit heart hydrolyzed the phospholipids of autoclaved E. coli maximally at pH 7.0 with 5.0 mM added CaCl2; EDTA was a potent inhibitor. More than 70% of the homogenate phospholipase A activity was sedimented at 100 000 x g. Homogenates dialyzed to pH 3.0 had a similar pH optima, but required less than 1.0 mM added CaCl2 for optimal activity. Sulfuric acid extraction of whole heart, and other rabbit organs, solubilized a calcium-dependent phospholipase A that was maximally active at pHs 7.0 to 7.5. Myocardial extracts were as active (approx. 60 nmol/h/mg) as acid extracts from rabbit lung, liver and kidney. Phospholipase(s) A with similar properties were solubilized by acid extraction of 12-day-old chick embryo myocytes (10 nmol/h/mg). Regardless of origin, the phospholipases A were absolutely specific for release of fatty acid from the 2-acyl position of phospholipids. Activity was inhibited by (i) pretreatment with p-bromo-phenacylbromide; (ii) the anesthetics, dibucaine and chlorpromazine; and (iii) the nonsteroidal antiinflammatory agents, indomethacin, ibuprofen and meclofenamate. Aspirin and dexamethasone had little or no effect on enzymic activity.