Abstract
The nitroreductase activity of aldehyde oxidase (EC 1.2.3.1), a molybdoflavoprotein present in the supernatant fraction from mammalian liver homogenates, was assessed. Nitrofurazone and the carcinogen 4-nitroquinoline-N-oxide were rapidly reduced to their corresponding hydroxyamino derivatives and a number of other nitro compounds of pharmacological interest were also reduced at significant rates; the range of nitro acceptor activity was limited, however; e.g., p-nitrobenzoate and p-nitrophenol did not undergo detectable reduction in the aldehyde oxidase system. Both aldehydic and N-heterocyclic substrates for the enzyme acted as electron donors; the most rapid rate of nitro reduction was observed with N1-methylnicotinamide as substrate. Under anaerobic conditions, the rate of nitrofurazone reduction was linear with time; exposure to atmospheric oxygen resulted in progressive inhibition of the reaction. The nitroreductase activity of aldehyde oxidase could be distinguished from that of xanthine oxidase by its susceptibility to inhibition by menadione, its lack of sensitivity to inhibition by allopurinol and its inability to utilize reduced nicotinamide adenine dinucleotide as electron donor. In a survey of commonly used species of laboratory animals, hepatic aldehyde oxidase-catalyzed nitroreductase activity was found to be highest in the rabbit and lowest in the rat and guinea pig. The combined molybdoflavoprotein nitrofurazone reductase activity (i.e., the activity attributable to xanthine oxidase plus aldehyde oxidase) amounted to approximately one-third of the total nitrofurazone reductase activity in rat, mouse, hamster and rabbit liver and one-fifth of the total activity in guinea-pig liver.
Footnotes
- Received October 23, 1972.
- Accepted January 10, 1973.
- © 1973 by The Williams & Wilkins Co.