NITRATE REDUCTASE IN PHOTOSYNTHETIC BACTERIUM, RHODOSPIRILLUM RUBRUM. PURIFICATION AND PROPERTIES OF NITRATE REDUCTASE IN NITRATE-ADAPTED CELLS1

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Abstract
1. From nitrate-adapted cells of Rhodospirillum rubrum, an active preparation of nitrate reducing enzyme was isolated in partially purified state. The enzyme was found to be localized in the chromatophores of the cell and, on sonication, readily released into the upernatant fraction. The purified enzyme, catalyzing the electron transfer between DPNH and nitrate, contained a b-type cytochrome, flavin and non-heme iron, which was removed on dialysis in the presence of cyanide. Besides DPNH, only methylviologen (reduced form) was effective as electron donor. 2. The effects of pH and the addition of various activators and inhibitors on the rate of nitrate reduction were investigated, using DPNH or reduced methylviologen as the electron donor. The oxidation-reduction of the flavin and the heme in the enzyme was followed spectrophotometrically. A pathway of electron in the nitrate reduction through this enzyme was proposed. 3. The nitrate reductase of this bacterium was compared with other nitrate reductases obtained from other sources, and the metabolic roles of this enzyme were discussed. In the nitrate-adapted cells of Rsp. rubrum, only one and the same enzyme was obtained under different growth conditions of nitrate assimilation (i. e., nitrate as N-source; light as energy source) and nitrate-respiration (i. e., in the dark; nitrate as hydrogen acceptor and N-source).