SOD AND CATALASE INACTIVATION BY SINGLET OXYGEN AND PEROXYL RADICALS

Both superoxide dismutase and catalase are readily deactivated by sing let oxygen and by the radicals produced in the pyrolysis of 2,2'-azo-b is-(2-amidinpropano) under aerobic conditions. The rate constant for t he loss of enzymatic activity induced by singlet oxygen are 3.9 X 10(7 ) and 2.5 X 10(7) M(-1) sec(-1) for SOD and catalase, respectively. Th e similarity between these values implies that in systems where SOD an d catalase are exposed to similar singlet oxygen concentrations, it ca n be expected a parallel inactivation of both enzymes. The inactivatio n of both enzymes by the radicals produced by 2,2'-azo-bis-(2-amidinop ropane) pyrolysis under aerobic conditions follows a first-order kinet ics at low enzyme concentrations and a zero-order kinetics at higher c oncentrations. Although at low enzymatic concentrations the rate of in activation of both enzymes is similar, this results from a compensatio n of effects because there are wide differences in the reactivity of b oth enzymes towards peroxyalkyl radicals. Catalase is considerably mor e reactive, but a large number of protein/radical reactive interaction s are needed to inactivate one enzyme. On the other hand, the reactivi ty of SOD is smaller, but the average enzyme activity decreases by nea rly 20% in each SOD/radical reactive interaction.