Detection of activating enzymes for 4-nitroquinoline 1-oxide activation with a microbial assay system.

4-Nitroquinoline 1-oxide (4NQO) damages bacterial genomes but not phage genomes. A reduction product of 4NQO, 4-hydroxyaminoquinoline 1-oxide (4HAQO), damages both the bacterial and phage genomes. These results imply that Salmonella typhimurium is able to convert 4NQO to 4HAQO and that 4HAQO reacts with the genomes. When phage P22 is treated with 4HAQO and assayed on S. typhimurium strains lysogenic for P221, a rapid inactivation of P22 and a greatly increased frequency of recombination between P22 and the prophage P221 are observed. With the use of this phage assay system, experiments were designed to search for activating enzymes which convert 4NQO to 4HAQO or a reactive intermediate that inactivates bacteriophage. When phage P22 was incubated with 0.1 mM 4NQO, 0.1 mM NADH, and bacterial protein fractions obtained by diethylaminoethyl cellulose column chromatography, it was found that only one protein peak was able to cause phage inactivation and recombination; this same peak was the only one with bacterial diaphorase and 4NQO-reducing activity. Similarly, ex periments with rat liver cytosol fractions showed that there are two peaks that activate 4NQO, and these also corresponded to diaphorase activity. These results suggest that diaphorase is an activating enzyme for 4NQO.