Nitric oxide reductases

Nitric oxide reductase (P) Nitrous oxide reductase (P) Ascorbate oxidase (P) Cytochrome oxidase (PM) Copper ATPase pumps (PM)... 

Nitric oxide and iron nitrosyl complexes have been observed in the reduction of nitrite by bacterial nitrite reductases, which contain iron chlorin or iron isobac-terichlorin [151]. A specific nitric oxide reductase also exists to convert NO to nitrous oxide [9]. Iron complexes of chlorins, isobacteriochlorins, and porphyrins, as well as ruthenium and osmium polypyridines, and cobalt and nickel... 

The work of Ye et al. (1991) was extended to include Tn5 mutants in nir genes for nitrite reductase of Pseudomonas fluorescens (Ye etal., 1992a) and Pseudomonas sp. strain G-179 (Ye et al., 1992b) which use, respectively, the cytochrome cd - and Cu-type nitrite reductase. The five mutants of P. fluorescens characterized not only lacked nitrite reductase and N0/H20- 0 exchange activities, but also showed levels of nitric oxide reductase activity that were diminished roughly by a factor of two. The reason for the decrease in nitric oxide reductase activity of the mutants is not clear, but may represent a change in... 

Although the nitrite reductases of denitrifying bacteria seem to be NO-pro-ducing reductases in vitro, we cannot so easily say that they similarly are NO-producing in vivo. It is not so rare for an enzyme to catalyze more than one reaction or be served by more than one substrate, but it is virtually without precedence for an enzyme to change its chemistry with the same substrate between in vivo and in vitro situations. The reduction of nitrite in vivo has been probed by several means which target the activity of either nitrite or nitric oxide reductase. 

In summary, a considerable body of enzymatic, genetic, and analytical data supports the view that the major, if not sole, pathway of denitrification involves NO as an obligatory intermediate and requires the action of nitric oxide reductase. On the other hand, the ability of nitrite to modify nitrosyl transfer ratios and the N isotope fractionation factor during its reduction, are consistent with the reductive scheme of Averill and Tiedje (1982). It was suggested (Goretski... 

IV. NITRIC OXIDE REDUCTASE, NITRIC OXIDE-CONSUMING ENZYME OF DENITRIFICATION PATHWAY... 

Spectra of nitric oxide reductase from Paracoccus denitrificans (batch eluate). Solid curve, enzyme as prepared (oxidized) dashed and dtit-dashed curves, reduced with a small excess of dithionite. Inset solid curve shows the second derivative of the dashed curve. The protein concentration was about 200 /ng/ml. From Dermastia et al. (1991). 

As far as we know, nitric oxide reductase has not been shown to catalyze the N0/H20-" 0 exchange reaction. 

But, because there was also a first-order term, reduction via a dinitrosyl complex may not be compulsory. It is doubtful that cytochromes could participate in NO reduction via dinitrosyl complexes, because of strong axial coordination of Fe by at least one protein ligand. It is of course possible that the nonheme iron of nitric oxide reductase is the actual site of reduction of NO. 

Turk and Hollocher (1992) have attempted to trap nitroxyl using the dithiol, dithiothreitol, during the reduction of NO by purified nitric oxide reductase from Pa. denitrificans. Because the dithiol served in this system as both electron donor to the enzyme and trap for nitroxyl, the ratio of thiol groups oxidized to NO consumed would have been 1 if nitroxyl trapping did not occur and 3 if nitroxyl... 

Deletion of the regulatory nirQ gene results simultaneously in a loss of the ability to reduce both nitrite and NO in P. stutzeri (Braun and Zumft, 1992). Nitrite reductase is synthesized and is active in vitro but nitric oxide reductase is synthesized in an inactive form. Although the exact function of the nirQ gene product is unknown, the gene encodes a protein homologous with the NtrC family of transcriptional activators (Zumft, 1993). 

Braun, C., and Zumft, W. G. (1991). Marker exchange of the structural genes for nitric oxide reductase blocks the denitrification pathway of Pseudomonas stutzeri at nitric oxide. . Biol. Chem. 266, 22785-22788. 

Carr, G. J., and Ferguson, S. J. (1990). The nitric oxide reductase of Paracoccus denitrifi cans. Biochem.. 269, 423-429. 

Costa, C., Macedo, A., Moura, 1., Moura, j. j. G., LeGall, J., Berber, Y., Liu, M.-Y., and Payne, W. J. (1990). Regulation of the hexaheme nitrite/nitric oxide reductase of Desulfovibrio desulfuricans, Wohnella succinogenes, and Escherichia coli. A mass spectro-metric study. FEBS Lett. 276, 67-70. 

Jones, A. M., and Hollocher, T. C. (1993), Nitric oxide reductase from Achromobacter cycloclastes. Biochim. Biophys. Acta 1144, 359-366. 

Korner, H. (1993). Anaerobic expression of nitric oxide reductase from denitrifying Pseudomonas stutzeri. Arch. Microbiol. 159, 410-416. 

Miyata, M., Matsubara, T., and Mori, T. (1969). Studies on denitrification XL Some properties of nitric oxide reductase. J. Biochem. (Tokyo) 66, 759-763. 

Nakahara, K., Tanimoto, T., Hatano, K., Usuda, K., and Shoun, H. (1993). Cytochrome P-450 55A1 (P-450dNlR) acts as nitric oxide reductase employing N ADH as the direct electron donor. J. Biol. Chem. 268, 8350-8355. 

Shapleigh, J. P., Davies, K. J. P., and Payne, W. J. (1987). Detergent inhibition of nitric-oxide reductase activity. Biochim. Biophys. Acta 911, 334-340. 

Zumft, W. G., Braun, C., and Cuypers, H. (1994). Nitric oxide reductase from Pseudo moruis stutzeri. Primary structure and gene organization of a novel bacterial cytochrome be complex. Eur. ]. Biochem. 219, 481-490. 

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