An Essential Arginine Residue in Porcine Phospholipase

Reaction of phenylglyoxal, a reagent specific for arginine residues, with porcine phospholipase Az results in complete elimination of catalytic activity. The modification reaction is markedly dependent on pH. Other dicarbonyl compounds such as 2,3-butanedione and 1,2cyclohexanedione also react with the enzyme to cause loss of activity but at significantly slower rates. At pH 7.0, the inactivation can be slightly retarded in the presence of Caz+ and almost completely prevented in the presence of n-alkylphosphorylcholine inhibitors. At pH 8.5, the n-alkylphosphorylcholine inhibitors are less effective. The decrease in enzymatic activity correlates with the modification of about 1 arginine residue/phospholipase A2 molecule. The data suggest that the arginine is involved in the binding of the phosphate portion of the substrate to the enzyme.