RT Journal Article SR Electronic T1 Mechanism of azoreduction of dimethylaminoazobenzene by rat liver NADPH-cytochrome P-450 reductase and partially purified cytochrome P-450. Oxygen and carbon monoxide sensitivity and stimulation by FAD and FMN. JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP 441 OP 448 VO 16 IS 3 A1 W G Levine A1 H Raza YR 1988 UL http://dmd.aspetjournals.org/content/16/3/441.abstract AB We have reported that the hepatocarcinogen dimethylaminoazobenzene (DAB) is reduced by rat liver microsomes in an oxygen- and carbon monoxide-insensitive manner and that activity is induced by clofibrate but no other recognized inducers of cytochrome P-450 activity. In the present study we have shown that the reaction proceeds in a partially purified reconstituted cytochrome P-450 system as well as with purified NADPH-cytochrome P-450 reductase alone. In the latter system, activity is totally inhibited in air whereas the former system is active in air as well as in a carbon monoxide atmosphere. Although clofibrate induces both DAB azoreductase and laurate hydroxylase activities, the suicide substrate 10-undecynoic acid blocks the latter but not the former, implying catalysis by distinct enzymes. FAD and FMN stimulate DAB azoreduction 40-50-fold by both NADPH-cytochrome P-450 reductase alone and by the reconstituted cytochrome P-450 system. However, it was shown that these flavins facilitate electron flow to DAB only from reductase and not from cytochrome P-450. The fact that the reconstituted system, which contains NADPH-cytochrome P-450 reductase, is oxygen insensitive suggests that there is an obligatory electron flow through cytochrome P-450 to DAB, bypassing the oxygen-sensitive step.