Purification and characterization of 1-nitropyrene nitroreductases from Bacteroides fragilis

We isolated four nitroreductases from Bacteroides fragilis GAI0624 and examined their physicochemical and functional properties. Two major enzyme activities were found in the adsorbed and unadsorbed fractions from DEAE-cellulose column chromatography. The adsorbed fraction was subjected to Sephadex G-200 column chromatography, and two further activities were separated. One has high nitroreductase activity (nitroreductase I), and the other has low activity and relatively high molecular weight (nitroreductase III). The nitroreductase I fraction was subjected to hydroxylapatite and chromatofocusing column chromatography, and nitroreductase I was purified about 416-fold with a yield of 6.77%. The unadsorbed fraction from DEAE-cellulose column chromatography was subjected to Sepharose 2B and Sepharose 6B column chromatography. Two enzyme activities were obtained by the Sepharose 6B column chromatography. One has high activity (nitroreductase II), and the other has low activity (nitroreductase IV). Nitroreductase II was rechromatographed by Sepharose 6B gel filtration and purified about 178-fold with a yield of 9.65%. The four enzymes (nitroreductases I, II, III, and IV) were shown to be different by several criteria. Their molecular weights, determined by gel filtration, were 52,000, 320,000, 180,000, and 680,000, respectively. The substrate specificity, the effect on mutagenicity of mutagenic nitro compounds, of nitroreductases I, III, and IV was relatively high for 1-nitropyrene, dinitropyrenes, and 4-nitroquinoline 1-oxide, respectively, but nitroreductase II had broad specificity. Nitroreductase activity required a coenzyme; nitroreductases II, III, and IV were NADPH linked, but nitroreductase I was NADH linked. All enzyme activity was enhanced by addition of flavin mononucleotide and inhibited significantly by dicumarol, p-chloromercuribenzoic acid, o-iodosobenzoic acid, sodium azide, and Cu2+.(ABSTRACT TRUNCATED AT 250 WORDS)