Nitroalkane Oxidation by Streptomycetes

Abstract

Crude cell-free extracts of nine strains of Streptomyces tested for nitroalkane-oxidizing activity showed production of nitrous acid from 2-nitropropane, 1-nitropropane, nitroethane, nitromethane, and 3-nitropropionic acid. These substrates were utilized in most strains but to a decreasing extent in the order given, and different strains varied in their relative efficiency of oxidation. p -Nitrobenzoic acid, p -aminobenzoic acid, enteromycin, and ω-nitro- l -arginine were not attacked. d -Amino acid oxidase, glucose oxidase, glutathione S -transferase, and xanthine oxidase, enzymes potentially responsible for the observed oxidations in crude cellfree extracts, were present at concentrations too low to play any significant role. A nitroalkane-oxidizing enzyme from streptozotocin-producing Streptomyces achromogenes subsp. streptozoticus was partially purified and characterized. It catalyzes the oxidative denitrification of 2-nitropropane as follows: 2CH 3 CH(NO 2 )CH 3 + O 2 → 2CH 3 COCH 3 + 2HNO 2 . At the optimum pH of 7.5 of the enzyme, 2-nitropropane was as good a substrate as its sodium salt; t -nitrobutane was not a substrate. Whereas Tiron, oxine, and nitroxyl radical acted as potent inhibitors of this enzyme, superoxide dismutase was essentially without effect. Sodium peroxide abolished a lag phase in the progress curve of the enzyme and afforded stimulation, whereas sodium superoxide did not affect the reaction. Reducing agents, such as glutathione, reduced nicotinamide adenine dinucleotide, and nicotinamide adenine dinucleotide phosphate, reduced form, as well as thiol compounds, were strongly inhibitory, but cyanide had no effect. The S. achromogenes enzyme at the present stage of purification is similar in many respects to the enzyme 2-nitropropane dioxygenase from Hansenula mrakii . The possible involvement of the nitroalkane-oxidizing enzyme in the biosynthesis of antibiotics that contain a nitrogen-nitrogen bond is discussed.