Radiation-induced inactivation of superoxide dismutase in nitrous oxide-saturated solutions. A kinetic model.

It has been reported that the inactivation yield of superoxide dismutase from bovine erythrocytes irradiated in N2O-saturated solutions increases exponentially with the initial enzyme concentration and that dose-response curves are non-exponential. The present work analyses these data using a kinetic model which indicates that the inactivation process is a second order reaction and that the reactivities of the active (Ea) and inactive (Ei) enzymes toward hydroxyl radical (.OH) are unequal. The calculated rate constants for the reactivities of Ea and Ei with .OH are 2.54 . 10(10) M-1 . s-1, respectively. The ratio between number of collisions and inactivation events is estimated at 20, in good agreement with a previous report. This model suggests that subunit exchange processes play an important role in the inactivation reaction.