Some properties of a nitrite reductase from Pseudomonas denitrificans

Abstract

A nitrite reductase from extracts of actively denitrifying Pseudomonas denitrificans (A.T.C.C. 13867) was purified 160-fold. The enzyme utilized reduced benzyl or methyl viologen, leucomethylene blue, or reduced FMN as hydrogen donor. NADH and NADPH were active only in the presence of a flavin carrier (riboflavin, FMN, or FAD). The purified enzyme reduced nitrite stoichiometrically to nitric oxide, while suspensions of whole cells reduced nitrite to a mixture of nitric oxide and nitrous oxide. Inhibitor studies indicated the participation of a metal(s) and -SH groups. The inhibition of nitrite reduction by 2,4-dinitrophenol was due to a chemical reaction resulting in a competition for reducing power at the reduced flavin level and not to its uncoupling activity. The 2,4-dinitrophenol was reduced chemically by FMNH to 2-amino-4-nitrophenol.