. Biological structure and function; proceedings. Biochemistry; Cytology. Light on 40 min. y^ ^^ Vit. K5 » Vlt. K3 Control DPN Light off Light off Fig. 8. Effect of vitamin K and other cofactors on the reduction of cytochrome C2 in cell-free preparations of Chronuitiinn. The cytochromes were oxidized by previous illumination (cf. Fig. 7). The reaction mixture included in a final volume of 3 -o ml., dialyzed cell-free suspension (PS) containing o-o6 mg. bacteriochloro- phyll, 0-02 /imole of purified cytochrome To and 0-03 /xmole of the respective cofactors. Difference in optical density was
. Biological structure and function; proceedings. Biochemistry; Cytology. Light on 40 min. y^ ^^ Vit. K5 » Vlt. K3 Control DPN Light off Light off Fig. 8. Effect of vitamin K and other cofactors on the reduction of cytochrome C2 in cell-free preparations of Chronuitiinn. The cytochromes were oxidized by previous illumination (cf. Fig. 7). The reaction mixture included in a final volume of 3 -o ml., dialyzed cell-free suspension (PS) containing o-o6 mg. bacteriochloro- phyll, 0-02 /imole of purified cytochrome To and 0-03 /xmole of the respective cofactors. Difference in optical density was measured on a Beckman DU spectro- photometer with an attached photomultiplier using cuvettes with the respective cofactor omitted as controls in each case (Nozaki, Ogata, and Arnon, [114]). LIGHT-INDUCED CHANGES IN CHLOROPHYLL New experimental evidence for the electron flow theory has come from the recent work of Arnold and Clayton [115] who, on illuminating bacterial chromatophores, observed temperature-independent (i K to 300°K) reversible spectral changes in the absorption bands of bacteriochlorophyll. These spectral changes in chlorophyll that are independent of temperature are consistent with the proposed electron shift that would result from the primary photochemical act (compare equations (2) and (2a)). 8. Multiple sites in cyclic photophosphorylation As already discussed, cyclic photophosphorylation is catalyzed by vitamin K and FMN and also by non-physiological factors such as phenazine methosulphate. This latter fact has given rise to questions whether vitamin K and FMN, or equivalent quinone and flavin consti- tuents of photosynthetic tissues, are to be considered the physiological catalysts of cyclic photophosphorylation or whether they are to be regarded as non-specific agents in no way distinguishable from non-physiological catalysts. The question was of special interest in connection with phenazine methosulphate because this dye has given rates of photosynthet
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