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  • Title: [The role of vitamin K3 in the hydroxylation of benz(a)pyrene in rat liver mitochondria after induction with 3-methylcholanthrene and phenobarbital].
    Author: Izotov MV, Shcherbakov VM, Devichenskiĭ VM, Lugovaia LV, Benediktova SA.
    Journal: Biokhimiia; 1987 Jul; 52(7):1072-9. PubMed ID: 3663746.
    Abstract:
    The "fast" phase reduction of microsomal cytochromes P-450 and P-448 and their benz(a)pyrene (BP) hydroxylase activity was investigated as a function of menadione concentrations. Within a narrow concentration range (1.5-3 microM) menadione activates cytochrome P-448 reduction and the BP hydroxylase activity. At higher concentrations menadione inhibits cytochromes P-450 and P-448 reduction and BP hydroxylation with participation of the both cytochromes. These data suggest that menadione molecules present in membrane lipids serve as an additional electron carrier to cytochrome P-448, the active site of which is embedded into lipids. The activating effect is unobserved is case of cytochrome P-450 with an active site localized in the aqueous phase. The number of different BP metabolites formed at low (3 microM) menadione concentrations in the microsomes of rats induced with 3-methylcholanthrene (MC) and phenobarbital (PB) was compared. In PB-induced microsomes the amount of 7,8-dihydrodiol rises whereas the total content of BP metabolites decreases. Contrariwise, in MC-induced microsomes the synthesis of all BP metabolites is augmented. Menadione has a very weak effect on the ratio of different BP metabolites in PB- and MC-microsomes, but strongly inhibits the formation of more polar metabolites. This results in a marked reduction of the number of "dangerous" BP diolepoxides.
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