Reduction of tertiary amine N-oxide by purified cytochrome P-450

Summary A reconstituted system containing cytochrome P-450 and NADPH-cytochrome c reductase, purified from phenobarbital-induced rabbit and rat liver microsomes, respectively, catalyzed anaerobic reduction of tiaramide N-oxide by NADPH at a rate comparable to that observed with intact rabbit liver microsomes. The reduction was inhibited by oxygen and carbon monoxide. When reduced methyl viologen was used as electron donor, the reduction proceeded at a much higher rate in the absence of NADPH-cytochrome c reductase. Preparations of various species of cytochrome P-450 purified from rabbit and rat liver microsomes and camphor-grown Pseudomonas putida exhibited nearly the same N-oxide reducing activity with reduced methyl viologen as donor despite their widely different specificities for hydroxylatable substrates.