An essential arginine residue in porcine phospholipiase A2.

Reaction of phenylglyoxal, a reagent specific for arginine residues, with porcine phospholipiase A2 results in complete elimination of catalytic activity. The modification reaction is markedly dependent on pH. Other dicarbonyl compounds such as 2,3-butanedione and 1,2-cyclohexanedione 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 Ca2+ and almost completely prevented in the presence of n-alkylphosphorylchline 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.