Protein Modifications by Glyoxal and Methylglyoxal During the Maillard Reaction of Higher Sugars

Summary The modification of N α -t-BOC-lysine, N α -t-BOC-arginine and lens crystallins by glyoxal and methylglyoxal has been investigated under physiological conditions. In incubations involving glyoxal, a novel amide-type crosslink (GX-amide-crosslink) was identified and correlated with N α -carboxymethyllysine (CML) levels. The formation of GX-amide-crosslink should proceed via the same reaction pathways as for CML. In incubations with methylglyoxal, the formation of N δ -(5-hydroxy-4,6-dimethylpyrimidine-2-yl)-ornithine (argpyrimidine) was established. Independent mechanistic studies point towards a synthesis via an intermediate reductone with a five-membered carbon backbone. GX-amide-crosslink and argpyrimidine were also formed from higher sugars, suggesting they may play a role in protein modification in vivo .