Position Specificity in n-Hexane Hydroxylation by Two Forms of Cytochrome P-450 in Rat Liver Microsomes

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Abstract
The hydroxylation of n-hexane by rat liver microsomes was studied and the contribution of different molecular species of cytochrome P-450 to the hydroxylation reaction was examined. In the case of untreated rats, the products of NADPH-dependent n-hexane hydroxylation were 1-, 2-, and 3-hexanols, and the major one was 2-hexanol. Phenobarbital (PB) treatment of animals resulted in a significant increase of the hydroxylation activity. The formation of 2- and 3-hexanols was much more significantly increased than that of 1-hexanol. On the other hand, 3-methylcholanthrene (MC) treatment stimulated the formation of 3-hexanol and the formation of the other two isomeric alcohols was rather decreased. These observations suggested the position specificities of the PB-inducible form (P-450(PB)) and MC-inducible form (P-450(MC)) of cytochrome P-450 in the hydroxylation of n-hexane. Inhibition experiments using antibodies specific to P-450(PB) and P-450(MC) also indicated that P-450(PB) was more active in the hydroxylation at the 2-position whereas P-450(MC) was more specific for the 3-position. NADPH-dependent n-hexane hydroxylation systems were reconstituted by the use of purified NADPH-cytochrome P-450 reductase and P-450(PB) or P-450(MC), and the activities of the reconstituted systems supported the proposed position specificities of these two forms of cytochrome P-450 in n-hexane hydroxylation.