Electron Spin Resonance Studies on the Mechanism of Enzyme Inactivation by Direct Action of Gamma Radiation'`

Electron spin resonance spectra of a sulfhydryl enzyme, urease, and a non-sulfhydryl enzyme, bacterial proteinase, were observed after exposure to irradiation of 7-rays. Urease showed a characteristic pattern to a sulfhydryl protein and bacterial proteinase to a non-sulfhydryl protein. A quantitative relationship among inactivation of the proteinase, intensity of ESR signal of the enzyme and irradiation dose of 1-rays, was measured. Whereas in an early process of the inactivation any significant increase of the intensity of ESR pattern was not observed, a parallel relationship between the inactivation of the enzyme and the increase of free radicals was found in a range from 100 kiloroentgen dose to 10 mega-roentgen dose of 7-rays and no significant increase of the free radicals was found con-trary to further progress of the inactivation of the enzyme in the course of the irradia-tion of larger doses than 10 megaroentgens. Possibility of conduction of electron vacancy from a damaged area of the enzyme molecule to an active center on the enzyme, and a inactivating mechanism by direct action of gamma radiation, were proposed and discussed