Abstract
Photoreactions of cytochrome b 6 have been studied using resolved chloroplast electron-transfer complexes. In the presence of Photosystem (PS) II and the cytochrome b 6- f complex, photoreduction of the cytochrome can be observed. No soluble components are required for this reaction. Cytochrome b 6 photoreduction was found to be inhibited by quinone analogs, which inhibit at the Rieske iron-sulfur center of the cytochrome complex, by the addition of ascorbate and by depletion of the Rieske center and bound plastoquinone from the cytochrome complex. Photoreduction of cytochrome b 6 can also be demonstrated in the presence of the cytochrome complex and PS I. This photoreduction requires plastocyanin and a low-potential electron donor, such as durohydroquinone. Cytochrome b 6 photoreduction in the presence of PS I is inhibited by quinone analogs which interact with the Rieske iron-sulfur center. These results are discussed in terms of a Q-cycle mechanism in which plastosemiquinone serves as the reductant for cytochrome b 6 via an oxidant-induced reductive pathway.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA) - Bioenergetics
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