Soluble Dissimilatory Nitrate Reductase Containing Cytochrome c from a Photodenitrifier, Rhodopseudomonas sphaeroides form a sp. denitrificans

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Dissimilatory nitrate reductase [nitrite:(acceptor) oxidoreductase, EC 1.7.99.4] from a denitrifying photosynthetic bacterium, Rhodopseudomonas sphaeroides forma sp. denituficans proved to be a soluble enzyme that could be purified 47-fold. It was labile, and contained cytochrome c, based on the results of specific staining for heme on polyacrylamide gel electrophoresis and on its absorption spectrum. Its physiological molecular weight was determined to be 112k, although heterogeneous molecular weights of 112k, 100k, 73k and 60k were found for different preparations. The optimum for enzyme activity was about pH 6, and the K_m for the nitrate was 1.6 mM. As an electron donor, benzyl viologen was very good; but NADH, NADPH, FAD, FMN, cytochromes b_2 and c_2, dichlorophenolindophenol and phenazine methosulfate were not effective. Bathophenanthroline and thiocyanate inhibited enzymatic activity. The addition of 1 mM tungstate to the growing culture in place of molybdate decreased the nitrate reductase in the cells, but a further addition of 1 mM molybdate stopped it. This nitrate reductase is believed to be a molybdo-iron protein similar to the enzymes from other bacteria with a nitrate respirating ability.
日本植物生理学会の論文