%0 Journal Article %A K. G. SYMMS %A M. A. JUCHAU %T THE ANILINE HYDROXYLASE AND NITROREDUCTASE ACTIVITIES OF PARTIALLY PURIFIED CYTOCHROMES P-450 AND P-420, AND CYTOCHROME b5 SOLUBILIZED FROM RABBIT HEPATIC MICROSOMES %D 1974 %J Drug Metabolism and Disposition %P 194-201 %V 2 %N 2 %X Purified cytochrome b5 and partially purified cytochromes P-450 and P-420 were compared with several other highly purified hemoproteins with respect to their capacity to catalyze the p-hydroxylation of aniline and the reduction of p-nitrobenzoic acid to the primary amine. In incubation flasks containing no added flavins, no nitroreductase and only minimal aniline hydroxylase activities could be detected regardless of the hemoprotein utilized as catalyst with the exception of cytochromes P-450 and P-420. In cytochrome P-450-catalyzed reactions, NADPH was two to five times more active than NADH, depending on the reaction conditions and substrate utilized. With all other hemoproteins tested, the two reduced nucleotides were approximately equally active. Additions of FMN to reaction flasks containing cytochrome P-450 resulted in a marked acceleration of aniline hydroxylation and nitro-group reduction if NADH were utilized as the initial electron donor; with NADPH as donor, however, addition of flavins resulted in a marked decrease in rates of both the hydroxylation and reduction reactions. Conversion of cytochrome P-450 to cytochrome P-420 resulted in a greater than 90% loss of aniline hydroxylase activity. Carbon monoxide (80:20, N2/CO) inhibited nitroreductase by 90% or more except in reactions catalyzed by cytochrome b5. All aniline hydroxylation systems were inhibited by 40-60% (80:20, CO/O2) except those catalyzed by cytochrome b5. Under certain sets of reaction conditions, cytochrome b5 and methemoglobin exhibited specific activities (in terms of monomer heme) nearly as high as those observed with cytochrome P-450 or whole microsomes. Copyright © 1974 by The American Society for Pharmacology and Experimental Therapeutics %U https://dmd.aspetjournals.org/content/dmd/2/2/194.full.pdf