Effects of cysteamine and of irradiation on microsomal membrane-bound enzymes

Changes in lipid peroxidation, drug-metabolizing enzymes and kinetic constants of ethylmorphine demethylation and of ethylmorphine interaction with cytochrome P-450 were examined after gamma-irradiation. The radiation-induced lipid peroxidation was increased with increasing radiation dose, while cytochrome P-450 content and ethylmorphine demethylase activity decreased. Of the enzyme kinetics parameters, Vmax was modified. Cysteamine protected against the effects of irradiation. This compound interacts with cytochrome P-450 and inhibits the drug-metabolizing enzyme system. Mechanisms of radiation damage, protective and toxic properties of cysteamine are discussed.