The oxidation-reduction potentials of electron carriers in chloroplast photosystem I fragments |
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Authors: | D B Knaff R Malkin |
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Institution: | Department of Cell Physiology, University of California, Berkeley, California 94720 U.S.A. |
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Abstract: | Oxidation-reduction titrations of several electron carriers found in chloroplast Photosystem I fragments have been performed. The midpoint potential of P700 in these fragments and in chloroplasts has been found to be +520 mV by optical absorbance methods or electron paramagnetic resonance spectroscopy. The copper-containing protein plastocyanin is present in Photosystem I fragments and has a midpoint potential of +320 mV, significantly less positive than the midpoint potential of cytochrome f in the same fragments, which was measured to be +375 mV. Photo-system I fragments contain two b cytochromes, a low-potential form of cytochrome b559 (Em = +110 mV) and cytochrome b563 (Em = ?100 mV). |
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