Effects of oxygen and transition metals on the advanced Maillard reaction of proteins with glucose.

The generation of fluorescence and 3-deoxyglucosone (3DG), browning, polymerization, and impairment of the amino acid residues of lysozyme incubated with glucose were investigated at 37 degrees C and 50 degrees C at pH 7.4 in a phosphate or TAPSO buffer under aerobic and non-aerobic conditions with or without DETAPAC as a chelating reagent. Browning, the generation of fluorescence, and polymerization were accelerated under the non-aerobic, compared to aerobic, conditions. Moreover, the formation of 3DG was also significantly increased under non-aerobic conditions. The incubation of both reaction systems resulted in noticeable losses of arginine and lysine residues. DETAPAC significantly inhibited the advanced Maillard reaction under both aerobic and non-aerobic conditions. However, DETAPAC had no effect on the impairment of lysine and arginine residues. The generation of fluorescence, browning and polymerization of lysozyme in the TAPSO buffer were markedly inhibited under both aerobic and non-aerobic conditions. These observations suggest that transition metals in the phosphate buffer may have accelerated the formation of Amadori compounds via Schiff's base. In addition, under non-aerobic conditions, the formation of advanced glycation end products from 3DG via Amadori compounds is presumed to be the major pathway, because the formation of N epsilon-(carboxymethyl)lysine, glyoxal, and glucosone was accelerated by an oxidative reaction catalyzed with transition metal ions. These presumptions are supported by the results from a lysozyme-3DG reaction system.