The nitrite oxidizing system of Nitrobacter winogradskyi |
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Authors: | Tateo Yamanaka Yoshihiro Fukumori |
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Institution: | Department of Life Science, Faculty of Science, Tokyo Institute of Technology, Tokyo, Japan |
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Abstract: | Abstract Cytochrome components which participate in the oxidation of nitrite in Nitrobacter winogradskyi have been highly purified and their properties studied in detail. Cytochrome a 1 c 1 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 a 1 c 1 and aa 3-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 cythochrome c could be pushed through prompt removal by cytochrome aa 3 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 a 1 c 1 with NO2? in vivo. |
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Keywords: | Nitrobacter winogradskyi Cytochrome NADPH Nitrite oxidizing system |
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