Characterization of Tryptophan Derivatives from the Reaction of N^α-Acetyl-tryptophan with Carbonyl Compounds

Abstract

To find the mechanism of the amino-carbonyl reaction of proteins with reducing sugars, we examined the reactivity of N^α-acetyl-tryptophan (N-Ac-Trp), a model of tryptophan residues, with various sorts of carbonyl compounds, formaldehyde, acetaldehyde, glyoxal, methylglyoxal, butanedione, and acetone, on incubation at pH 6.8 and 50°C. Aldehydes reacted with N-Ac-Trp, but ketones did not.
The most abundant reaction product between N-Ac-Trp and glyoxal (Trp-GO-1) was identified as N^α-acetyl-1-(2-hydroxy-1-oxoethyl)-L-tryptophan and that between N-Ac-Trp and methylglyoxal (Trp-MG-1) was identified as N^α-acetyl-1-(1-hydroxy-2-oxopropyl)-L-tryptophan. From the UV spectrum, a major reaction product between N-Ac-Trp and 3-deoxyglucosone (Trp3DG-1) was supposed to be analogous to Trp-MG-1.
While Trp-GO-1 polymerized itself very little, Trp-MG-1 did produce some polymers. This suggests that Trp-MG-1 and Trp-3DG-l may participate in the crosslinking of proteins.