ADRENAL ACTIVATION OF CARBON-TETRACHLORIDE - ROLE OF MICROSOMAL P450 ISOZYMES

Previous investigations demonstrated that carbon tetrachloride (CCl4) was activated by adrenal microsomes, resulting in various functional c hanges and ultimately in necrosis of the zona reticularis of the gland . Experiments were done to identify the adrenal P450 isozyme(s) involv ed in the bioactivation of CCl4. Incubation of microsomes from the zon a reticularis (ZR) of the guinea pig adrenal cortex with CCl4 plus NAD PH caused initiation of lipid peroxidation, covalent binding of CCl4-d erived radioactivity to protein, and degradation of cytochrome(s) P450 . Preincubation of the microsomal preparations with inhibitory antibod ies to P450(17 alpha) or P450(C21) decreased the corresponding enzyme activities (17 alpha-hydroxylation and 21-hydroxylation), but did not affect the activation of CCl4. 1-Aminobenzotriazole (ABT), a suicide i nhibitor of some P450 isozymes, decreased the enzyme activities cataly sed by an adrenal 52 000 Da (52 kDa) isozyme, but had no effect on the function of P450(17 alpha) or P450(C21). However, ABT completely inhi bited the CCl4-induced LP and covalent binding in adrenal microsomes. The results indicate that adrenal CCl4 activation is catalysed by the 52 kDa P450 isozyme and not by the steroid hydroxylases, Localization of the 52 kDa isozyme to the ZR probably accounts for the selective ne crosis of this region of the gland by CCl4.