. Biological structure and function; proceedings. Biochemistry; Cytology. FHOTOSYNTHETIC PHOSPHORYLATION AND THE ENERGY CONVERSION PROCESS 359 Reversible oxidation of Chromatium cytochromes by light LIGHT t. 400 450 500 550 600 , Fig. 7. Successive oxidation by light and reduction in the dark of cytochromes in cell-free preparations of Chromatium. The reaction mixture included in a final volume of 3-0 ml., chromatophores (P) containing o-o6 mg. bacteriochlorophyll and supernatant fluid (S) corresponding to 0-5 mg. bacteriochlorophyll. A small amount of Xa.,So04 was previously added to S, which
. Biological structure and function; proceedings. Biochemistry; Cytology. FHOTOSYNTHETIC PHOSPHORYLATION AND THE ENERGY CONVERSION PROCESS 359 Reversible oxidation of Chromatium cytochromes by light LIGHT t. 400 450 500 550 600 , Fig. 7. Successive oxidation by light and reduction in the dark of cytochromes in cell-free preparations of Chromatium. The reaction mixture included in a final volume of 3-0 ml., chromatophores (P) containing o-o6 mg. bacteriochlorophyll and supernatant fluid (S) corresponding to 0-5 mg. bacteriochlorophyll. A small amount of Xa.,So04 was previously added to S, which was then dialyzed against 0-2 M tris buffer, pH 7-8 prior to use. The reaction was carried out at room temperature. Gas phase argon. Difference spectra, using the dark treatment as control, were made in Thunberg type cuvettes, with a Gary recording spectro- photometer. Illumination was by a tungsten lamp (35 000 Lux). (Nozaki, Ogata, and Arnon [i 14]). EFFECT OF VITAMIN K In fresh preparations of chromatophores the reduction of oxidized cytochrome in the dark was not influenced by the additions of added cofactors (compare Table I). However, as shown in Fig. 8, in aged prepara- tions, the reduction of the oxidized cytochromes was greatly accelerated by the addition of vitamin K, either in the oxidized form (vitamin K3) or in the reduced form (vitamin K5). The effect of vitamin K, as an electron carrier in accelerating the reduction of oxidized cytochrome depended on the presence of chromatophores. Without chromatophores, using a purified cytochrome Co, a hundred-fold greater concentration of reduced vitamin K was required to reduce the oxidized cytochrome. The observed effects of vitamin K in catalyzing the reduction of cyto- chromes which had been oxidized in light, support the electron flow- theory [94] for cyclic photophosphorylation. This theory assigns to- vitamin K, or some analogous quinone, a role of an intermediate electron carrier in the electron transport chain assoc
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