Two Classes of Azo Dye Reductase Activity Associated with Rat Liver Microsomal Cytochrome P-450

Abstract

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).