Studies in the reaction of amino and imino compounds with sugars: the reaction of histidine with glucose

Abstract

The combination of histidine with glucose has been examined with varying concentrations of histidine (0.067 to 0.016 [image]) and glucose (up to 1.2 [image]) over the pH range 5-9 and at 20[degree], 30[degree], 40[degree] and 50[degree], both aerobically and anaerobically, by measuring the pH depressions which follow the mixing of the solutions. A series of subsequent steady pH states having successively greater pH depression values was found. No combination was found within the approximate pH range 5-6.5. In the 1st steady pH state, over the approximate range pH 8-9, the results are in agreement with 1 glucose molecule combining with 1 molecule of anionic histidine. The equilibrium constants of the 1st steady pH state decreased with rise in temperature, showing the reaction to be exothermic. The pH depressions obtained for the 1st steady pH state were the same whether aerobic or anaerobic conditions were employed. However, under conditions involving both high initial pH values and high glucose concentrations, the aerobic pH depressions were somewhat higher in value. In subsequent steady pH states, particularly at the higher temperatures, the aerobic pH depressions were noticeably higher. Browning was noted as starting at the end of the 2d or the beginning of the 3d steady pH state. Its intensity was found to increase with rise in initial pH, glucose concentration and temperature, but to decrease in presence of air.