Electron transfer components in the photosynthetic system of the diatom Navicula pelliculosa.

Abstract

From Navicula pelliculosa , cytochrome c -554 (an f -type cytochrome), NADP + reductase (NADPH: (acceptor) oxidoreductase, EC 1.6.99.1) and ferredoxin were isolated and purified. Electron transfer reactions related to photosynthesis were investigated with these purified components. Cytochrome c -554 showed absorption maxima at 418, 523 and 554 mμ in the reduced form; the ratio of A γ (reduced)/ A γ (reduced) was 6.77. E m,7 of the cytochrome was about +0.34V at pH 7.0. Oxidized ferredoxin exhibited absorption peaks at 442 and 466 mμ; ϵ 422m μ was 6.9·10 3 1·mole −1 ·cm −1 on the basis of non-haem iron. Reduced benzylviologen could function as electron donor in the reduction of NADP + , catalyzed by the reductase. Ferredoxin facilitated this reaction. Na 2 S 2 O 4 -reduced ferredoxin also functioned as sole electron donor. NADP + reductase showed the absorption spectrum of a flavoprotein with peaks around 400 mμ and 460 mμ; a trichloroacetic acid extract of the enzyme showed the absorption spectrum of a typical flavin. The flavin derived from the enzyme was not FMN, but probably FAD. The enzyme anaerobically reduced NADP + with reduced benzylviologen, very rapidly reduced cytochrome c -554 with NADPH in the presence of ferredoxin, and possessed both NADPH-2,6-dichlorophenolindophenol reductase and transhydrogenase activities.