On the Mechanism of the Radiation-induced Inactivation of Ribonuclease in Dilute Aqueous Solution

Abstract

Pulse radiolysis data from ribonuclease solutions have been used to aid the interpretation of the mechanism of the radiation-induced inactivation of this enzyme. Activity measurements show that in γ-irradiated dilute aqueous solution, hydrated electrons do not contribute to the inactivation process. In deoxygenated solution, 90 per cent of the inactivation process is due to reactions of OH radicals with the remainder attributable to reactions of hydrogen atoms. Pulse radiolysis studies show the formation of three transient spectra which have been assigned respectively to reactions of OH, H and e_aq⁻ with the enzyme. It is concluded that the spectrum of the OH-induced transient contains contributions from OH-adduct spectra of the ring-containing amino acids and that some of the short-lived species are involved in the initial stages of the inactivation process.