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Purification and properties of a dissimilatory nitrite reductase of a denitrifying phototrophic bacterium
Authors:Sawada  Eiko; Satoh  Toshio; Kitamura  Hiroshi
Institution:Department of Biology, Faculty of Science, Tokyo Metropolitan University Fukazawa 2-1-1, Setagayaku, Tokyo 158, Japan
Abstract:Nitrite reductase nitric-oxide : (acceptor) oxidoreductase,EC 1.7.2.1 EC] ] from a denitrifying phototrophic bacterium, Rhodopseudomonassphaeroides forma sp. denitrificans, was purified. The molecularweight of the enzyme, estimated by gel-filtration, was 80,000.Sodium dodecyl sulfate polyacrylamide gel electrophoresis ofthe purified enzyme showed a single 39,000 molecular weightband, indicating that the enzyme was composed of two subunitsof identical molecular weight. The oxidized form of the enzymeexhibited maximum absorption at 280 nm, 450 nm and 590 nm, andthe reduced form only at 280 nm. The ESR spectrum of a frozensolution of the oxidized enzyme showed a typical spectrum patternof a copper protein, suggesting that two types of Cu2+ existedwithin the enzyme. Estimates with an atomic absorption spectrophotometer,revealed two copper atoms per molecule. The optimum pH of theenzyme was 7.0. Km for nitrite was estimated to be 51 µM,and the optimum temperature, 30?C. The enzyme was inhibitedby CO, potassium cyanide and diethyldithiocarbamate and activatedby monoiodoacetate. Phenazine methosulfate, 2,6-dichlorophenolindophenol,horse heart cytochrome c, and cytochrome c2 from this bacteriumwere suitable electron donors. The enzyme also showed cytochromec oxidase activity. (Received May 4, 1978; )
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