Benzpyrene hydroxylases

The intense interest in this and related enzyme activities is consequential to the central role that 3,4-benzpyrene plays in the aetiology of human lung cancer.

Several publications have briefly reported on benzpyrene hydroxylase without specifying the site of hydroxylation. Many publications (see 3,4-Benzpyrene) report on 3-hydroxylation, but a significant number additionally report hydroxylation at positions 1 (rat, man and sole, e.g [A458, C473, J94]), 4 (rat [C204]), 7 (rat, man, mouse and scup, e.g. [A458, B122, D965, G445]), 8 (rainbow trout [A1424]) and 9 (rat, monkey, hamster, rabbit, mouse, man and Saccharomyces, e.g. [A458, A2327, A2379, A2814, A3326, A3412, A3681]). 3-Hydroxylation (E.C. 1.14.14.2) occurs in a large range of species, including man, rat [A13], monkey [A1869], tree shrew, pig [A1997], rabbit [A2729], camel [H103], quokka, kangaroo, bandicoot, [A2420], mouse [A3681], guinea pig [B82], pigeon, crow, kite, egret [C307], trout [A2145], goldfish, bullhead [D465], bluegill [E480], scup [D965], sole [G374], killifish [B259], mullet [C141], barnacle [B744], Saccharomyces [A3326] and Candida [B775].

Studies on monohydroxylation of benzpyrene and other polynuclear hydrocarbons is complicated by the ready dehydration of dihydrodiols under acid conditions to monophenols; the former are metabolic products formed by hydration of epoxides generated in metabolism of polynuclear hydrocarbons. In rat, it has been suggested that at least some 3-hydroxybenzpyrene is formed by a spontaneous rearrangement of benzpyrene-2,3-oxide [A3277].

In man, 3-hydroxylation has been described in bronchus [A13], placenta, [A114], lung [A1644], liver [A2379], blood [B122], hair follicle [B350], bladder [C138], hepatoma [E480], melanocyte [G360] and P450 isozymes [H10]. Placental enzyme is largely microsomal [A985].

In man and rat, liver enzyme is primarily microsomal, and is activated by low molecular weight cofactors. In man, the activity is twice as high in smokers compared with non-smokers. In rat, activity is three times higher in males than in females, but there are only small sex differences in man, rabbit and guinea pig [A313]. Rat liver microsomal enzyme activity is reduced by extraction with organic solvents [A331].

In rabbit, the liver enzyme activity remains low up to 16 days after birth, and then increases to or above the adult level at about 30 days [A1980].

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