Studies on the mechanism of action of ionizing radiations. XI. Inactivation of yeast alcohol dehydrogenase by x-irradiation

Crystalline yeast alcohol dehydrogenase was readily inactivated on x-irradiation of dilute aqueous solutions. The degree of inactivation was proportional to the x-ray dose, and the ionic yield was 1.1. The enzyme was completely protected from x-ray inactivation by the addition of glutathione, whereas glutamic acid had no effect at all. Glutathione, added after x-irradiation, produced only partial reactivation. Hydrogen peroxide, at concentrations produced on x-irradiation of water with x-ray doses 200 times higher than the dose required for complete inactivation, had no effect at all. Inhibition by x-rays is attributed to oxidation of —SH groups of the protein by the free radicals OH and O₂H formed on x-irradiation of water.