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Vol. 26, Issue 5, 483-489, May 1998
Laboratory of Genetic and Biochemical Toxicology, Istituto di
Mutagenesi e Differenziamento, Consiglio Nazionale delle Ricerche
Western blot analyses of liver microsomes from 13 male and 12 female monkeys demonstrated that in each sample a variable amount of a
cytochrome P450 (P450) protein, likely monkey P450 2E1, cross-reacted with anti-rat P450 2E1 antibodies. Therefore, the involvement of monkey
2E1 in the oxidation of typical substrates for 2E1 from other species,
such as dimethylnitrosamine (DMN), p-nitrophenol (pNP),
chlorzoxazone (CLZ), and aniline, was investigated. Kinetic studies
using microsomes from five male and five female monkeys showed that CLZ
and pNP hydroxylations were monophasic, with apparent KM values of 77 and 14 µM,
respectively, whereas aniline hydroxylation and DMN demethylation were
multiphasic, suggesting that P450s other than 2E1 were involved in
catalyzing the latter two reactions. When correlation analyses were
performed using several monooxygenase activities determined in male and
female monkey liver specimens, it was found that immunodetectable 2E1
contents were highly correlated (r
0.75) with CLZ
and pNP hydroxylations, weakly correlated (r = 0.6)
with aniline hydroxylation, and not correlated with DMN demethylation
or other monooxygenase activities; CLZ hydroxylation was strongly
correlated with pNP hydroxylation, weakly correlated with aniline
hydroxylation, and not correlated with DMN demethylation. Inhibition
experiments showed that CLZ and pNP hydroxylations were immunoinhibited
by 60-80% by anti-rat P450 2E1 and were inhibited by the prototypical
2E1 inhibitor 4-methylpyrazole with IC50 values of 1.5 and 13 µM, respectively. In conclusion, the findings provide evidence that P450 2E1 is constitutively and equally expressed in male
and female monkey liver and it exerts a major role only in
hydroxylation of CLZ and pNP.
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