Two Classes of Azo Dye Reductase Activity Associated with Rat Liver Microsomal Cytochrome P-450
Reduction of carcinogenic and other azo dyes by rat liver microsomes is catalyzed by NADPH-cytochrome P-450 reductase and cytochrome P-450 (P-450). Dimethylaminoazobenzene (DAB), a lipid soluble hepatocarcinogen, is reduced by a form of P-450 which is selectively induced by clofibrate but not other commonly used inducing agents; reduction is insensitive to O2 and CO (Raza and Levine, 1986; Levine and Raza, 1988). In contrast, microsomal reduction of amaranth, a water soluble dye, is catalyzed by forms of P-450 which are induced by phenobarbital and methylcholanthrene; reduction is inhibited by O2 and CO (Fujita and Peisach, 1978). Oxygen sensitivity of azoreduction is attributed to reoxidation of the 1-electron reduced free radical intermediate with formation of superoxide (Mason et al., 1978; Peterson et al., 1988). It follows that reduction of 2’-COOH-DAB (methyl red) by NAD(P)H:quinone reductase is oxygen insensitive since this enzyme contains two molecules of FAD and catalyzes a 2-electron reduction of the dye (Huang et al., 1979).
KeywordsMethyl Orange Nicotinamide Adenine Dinucleotide Phosphate Quinone Reductase Oxygen Sensitivity Reconstituted System
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- Levine, W. G. and Raza, H. (1988). Mechanism of azoreduction of dimethylamino azobenzene by rat liver NADPH-cytochrome P-450 reductase and partially purified cytochrome P-450. Oxygen and carbon monoxide sensitivities and stimulation by FAD and FMN. Drug Metab. Dispos. 16, 441–448.PubMedGoogle Scholar
- Mason, R. P., Peterson, F. J. and Holtzman, J. L. (1978). Inhibition of azoreductase by oxygen. The role of the azo anion free radical metabolite in the reduction of oxygen to superoxide. Mol. Pharmacol. 4, 665–671.Google Scholar
- Peterson, F. J., Holtzman, J. L., Crankshaw, D. and Mason, R. P. (1988). Two sites for azoreduction in the monoxygenase system. Mol. Pharmacol. 34, 597–603.Google Scholar