Reaction of glycolaldehyde with proteins: latent crosslinking potential of alpha-hydroxyaldehydes

The Schiff base adducts of glyceraldehyde with hemoglobin undergo Amadori rearrangement to form stable ketoamine structures; this reaction is similar to the nonenzymic glucosylation of proteins. In the present studies the analogous rearrangement of the Schiff base adducts of glycolaldehyde with proteins has been demonstrated. However, the Amadori rearrangement of the Schiff base adduct produces a new aldehyde function, an aldoamine, which is generated in situ and is capable of forming Schiff base linkages with another amino group, leading to covalent crosslinking of proteins. Sodium dodecyl sulfate gel electrophoresis of the glycoaldehyde-RNase A adduct showed the presence of dimers, trimers, and tetramers of RNase A, demonstrating the crosslinking potential of this alpha-hydroxyaldehyde. The crosslinked products exhibited an absorption band with a maximum around 325 nm and fluorescence around 400 nm when excited at 325 nm. The crosslinking reaction, the formation of a 325-nm absorption band, and the development of fluorescence were prevented when the incubation was carried out in the presence of sodium cyanoborohydride. This finding indicates that the Amadori rearrangement that generates a new carbonyl function is a crucial step in this covalent crosslinking. Glycolaldehyde could be a bifunctional reagent of unique utility because its crosslinking potential is latent, expressed only upon completion of the primary reaction.