RADIATION-INDUCED INACTIVATION OF FLAVOCYTOCHROME B(2) IN DILUTE AQUEOUS-SOLUTION

Effect of gamma radiation on flavocytochrome b(2) in dilute aqueous so lution was studied. A study of the effect of the radiolytically produc ed inorganic free-radical anions such as I-2(-), BT2- and (SCN)(2)(.-) on the enzyme activity indicates the involvement of cysteine and tyro sine residues in the catalytic activity of flavocytochrome b(2). The c hanges in kinetic parameters, i.e., Michaelis-Menten constant K-m and maximal velocity V-max, due to irradiation under different conditions suggest that radiation induced enzyme inactivation is the result of de struction of active-site residues as well as modification of the subst rate binding site. Fluorescence studies of unirradiated and irradiated enzyme reveal that FMN (flavin mononucleotide) is inaccessible to wat er radicals.