Protection by histidine against oxidative inactivation of AMP deaminase in yeast

Oxidative inactivation of AMP deaminase and its protection were analyzed under the in situ conditions of yeast cells. AMP deaminase was readily inactivated by an exposure to hydrogen peroxide plus copper in permeabilized yeast cells. Addition of ascorbic acid further enhanced the inactivation of the enzyme, suggesting the hydroxyl radical produced by the Fenton reaction is responsible for the inactivation of the enzyme. Addition of histidine caused an effective protection against the inactivation of AMP deaminase by hydrogen peroxide-induced hydroxyl radical. The concentration of histidine required for half-maximal effect was within physiological range. Cysteine showed less effective protection against oxidative inactivation. Other amino acids as potent copper-chelating agents as well as trolox and taurine showed little or no effect. Histidine can act as a physiological "antioxidant" in yeast cells.