Bacterial cytochrome c nitrite reductase: new structural and functional aspects

• Published in: Journal of inorganic biochemistry Vol. 79; no. 1; pp. 381 - 385
• Main Authors: Stach, Petra, Einsle, Oliver, Schumacher, Wolfram, Kurun, Ersin, M.H. Kroneck, Peter
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.04.2000
• Subjects: Binding Sites; Cytochrome c Group - chemistry; Cytochrome c Group - metabolism; Cytochrome c nitrite reductase; Electron Spin Resonance Spectroscopy - methods; EPR spectroscopy; Epsilonproteobacteria - enzymology; Heme - chemistry; Kinetics; Models, Molecular; Multiheme protein; Nitrite Reductases - chemistry; Nitrite Reductases - metabolism; Nuclear Magnetic Resonance, Biomolecular - methods; Protein Conformation; Spectrophotometry; Substrate Specificity; Cytochrome c nitrite reductase; Multiheme protein; EPR spectroscopy
• ISSN: 0162-0134; 1873-3344
• DOI: 10.1016/S0162-0134(99)00248-2

Cytochrome c nitrite reductase catalyzes the six-electron reduction of nitrite to ammonia as a key step within the biological nitrogen cycle. Most recently, the crystal structure of the soluble enzyme from Sulfurospirillum deleyianum could be solved to 1.9 Å resolution. This set the basis for new experiments on structural and functional aspects of the pentaheme protein which carries a Ca(2+) ion close to the active site heme. In the crystal, the protein was a homodimer with ten hemes in very close packing. The strong interaction between the nitrite reductase monomers also occurred in solution according to the dependence of the activity on the protein concentration. Addition of Ca(2+) to the enzyme as isolated had a stimulating effect on the activity. Ca(2+) could be removed from the enzyme by treatment with chelating agents such as EGTA or EDTA which led to a decrease in activity. In addition to nitrite, the enzyme converted NO, hydroxylamine and O-methyl hydroxylamine to ammonia at considerable rates. With N 2O the activity was much lower; most likely dinitrogen was the product in this case. Cytochrome c nitrite reductase exhibited a remarkably high sulfite reductase activity, with hydrogen sulfide as the product. A paramagnetic Fe(II)–NO, S=1/2 adduct was identified by rapid freeze EPR spectroscopy under turnover conditions with nitrite. This potential reaction intermediate of the reduction of nitrite to ammonia was also observed with PAPA NONOate and Spermine NONOate.