title: The nitrite oxidizing system of Nitrobacter winogradskyi.
abstract: Cytochrome components which participate in the oxidation of nitrite in Nitrobacter winogradskyi have been highly purified and their properties studied in detail. Cytochrome a1c1 is an iron-sulphur molybdoenzyme which has haems a and c and acts as a nitrite-cytochrome c oxidoreductase. Cytochrome c-550 is homologous to eukaryotic cytochrome c and acts as the electron mediator between cytochrome a1c1 and aa3-type cytochrome c oxidase. The oxidase is composed of two kinds of subunits, has two molecules of haem a and two atoms of copper in the molecule, and oxidizes actively eukaryotic ferrocytochrome c as well as its own ferrocytochrome c-550. Further, a flavoenzyme has been obtained which has transhydrogenase activity and catalyses reduction of NADP+ with benzylviologen radical. This enzyme may be responsible for production of NADPH in N. winogradskyi. The electron transfer against redox potential from NO2- to cytochrome c could be pushed through prompt removal by cytochrome aa3 of H+ formed by the dehydrogenation of NO2- + H2O. As cytochrome c in anaerobically kept cell-free extracts is rapidly reduced on addition of NO2-, a membrane potential does not seem necessary for the reduction of cytochrome c by cytochrome a1c1 with NO2- in vivo.
authors.affiliation: Department of Life Science, Faculty of Science, Tokyo Institute of Technology, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Yamanaka
authors.forename: Y
authors.initials: Y
authors.lastname: Fukumori
mesh_terms: D000595:Amino Acid Sequence; D003574:Cytochrome c Group / Q000032:analysis; D003576:Electron Transport Complex IV / Q000032:analysis; D008969:Molecular Sequence Data; D009247:NADH, NADPH Oxidoreductases / Q000032:analysis; D009572:Nitrite Reductases / Q000032:analysis; D009573:Nitrites / Q000378:metabolism*; D009576:Nitrobacter / Q000201:enzymology / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D003574:Cytochrome c Group; D009573:Nitrites; C031732:cytochrome C-550; D009247:NADH, NADPH Oxidoreductases; D009572:Nitrite Reductases; D003576:Electron Transport Complex IV