EXPLORING BORATE-ACTIVATED ELECTRON-RICH GLYOXALS AS THE ARGININE-REACTIVITY PROBES - THE REACTIVITIES OF FUNCTIONALLY CRITICAL ARGININES IN SOME REPRESENTATIVE ENZYMES

4-Substituted styrylglyoxals have been synthesized and found to benefit from borate catalysis to serve as highly reactive arginine modifiers. A study of the mechanism in arginine modification has affirmed: (i) the role of electronic effects in modulating the arginine reactivity in alpha-dicarbonyls, (ii) the intermediacy in the reaction of a reversible arginine-alpha-dicarbonyl complex and (iii) the identity of the nucleophilic attack at ketone as the rate determining step in the arginine reaction with arylglyoxals. 4-Methoxystyrylglyoxal and 4-(N,N-dimethyl-amino)phenylglyoxal were used as the probes in analyzing some representative enzymes for the reactivities of their susceptible arginyls. The susceptible arginyls in lactate and malate dehydrogenases were thus found to be appreciably reactive while those in carboxypeptidase-A and pyruvate kinase were only moderately reactive.