Spectroscopic studies of the protein-methylglyoxal adduct.

Spectroscopic measurements are reported for the effects of pH, time, solvent, and chemical modification of arginine and lysine side chains on the reaction of proteins with methylglyoxal. The reaction responsible for the appearance of a brown coloration and increased submolecular electronic activity in the proteins involves the epsilon-amino groups of the lysine residues. It is concluded that the primary step in the reaction involves the formation of a Schiff base linkage between the lysine side chain and methylglyoxal. These findings reaffirm the concept that, by the formation of Schiff bases, aldehydes can act as electron acceptors in charge transfer interactions with proteins.