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Mechanism of nitrite reduction to nitrous oxide in a photodenitrifier, Rhodopseudomonas sphaeroide forma sp. denitrificans

1985; Elsevier BV; Volume: 841; Issue: 2 Linguagem: Inglês

10.1016/0304-4165(85)90022-4

1872-8006

Katsuro Urata, Takeshi Satoh,

Photoreceptor and optogenetics research

The mechanism of anaerobic reduction of NO2− to N2O in a photodenitrifier, Rhodopseudomonas sphaeroides forma sp. denitrificans, was investigated. With ascorbate-reduced phenazine methosulfate (PMS) as the electron donor, the nitrite reductase of this photodenitrifier reduced NO2− to NO and a trace amount of N2O. With dithionite-reduced benzyl viologen as the electron donor, the major product of NO2− reduction was NH2OH, and a trace amount of N2O was also produced. The nitrate reductase itself had no NO reductase activity with ascorbate-reduced PMS. It was concluded that the essential product of NO2− reduction by the purified nitrite reductase is NO. Chromatophore membranes stoichiometrically produced N2O from NO2− with any electron donor, such as dithionite-redduced benzyl viologen, ascorbate-reduced PMS or NADH/FMN. The membranes also contrained activity of NO reduction of N2O with either ascorbate-reduced PMS or duroquinol. The NO reductase activity with duroquinol was inhibited by antimycin A. Stoichiometric production of N2O from N2− also was observed in the reconstituted NO2− reduction system which contained the cytochrome bc1 complex, cytochrome c2, the nitrite reductase and duroquinol as the electron donor. The preparation of the cytochrome bc1 complex itself contianed NO reductase activity. From these results the mechanism of NO2− reduction to N2O in this photodenitrifier was determined as the nitrite reductase reducing NO2− to NO with electrons from the cytochrome bc1 complex, and NO subsequently being reduced, without release, to N2O with electrons from the cytochrome bc1 complex by the NO reductase, which is closely associated with the complex.