REACTION OF ALDOSES WITH AMINO-ACIDS AND PROTEINS .1. REACTION OF LYSINE WITH ALDOSES

The reactivity of amino acids with trioses and hexoses under physiological conditions (37°, pH 7.5) has been investigated. The most reactive species were lysine, glyceraldehyde, and 2-amino-2-deoxyglucose. They generated yellow, oligomeric compounds having molecular weights in the range 500-1000 and pI values in the range pH 4-6. In the Lys-glyceraldehyde adduct, the ε-amino group is incorporated into a pyrrole-type structure, which gives a positive reaction with the Pauly reagent. The largest oligomers correspond to the condensation of 4 mol of Lys with 8-10 mol of glyceraldehyde. It is hypothesised that the primary Amadori-compound rearranges during the Maillard reaction to give browning products, since no yellow oligomers are produced if the Lys-aldehyde adduct is reduced immediately with cyanoborohydride.