Effect of oxidation-reduction potential on light-induced cytochrome and bacteriochlorophyll reactions in chromatophores from the photosynthetic green bacterium Chlorobium |
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Authors: | David B Knaff Bob B Buchanan Richard Malkin |
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Institution: | Department of Cell Physiology, University of California, Berkeley, Calif. 94720 U.S.A. |
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Abstract: | The reaction center bacteriochlorophyll of Chlorobium thiosulfatophilum has a midpoint oxidation-reduction potential (Em) of +330 mV. Its photooxidation is unaffected by oxidation-reduction potentials in the range from +260 mV to ?70 mV but on further reduction is attenuated to zero in a one-electron transition with an Em of ?130 mV.A c-type cytochrome with an Em of +220 mV and absorption maxima at 551–552 nm (α-band) and 420 nm (γ-band) is present in Chlorobium chromatophores and undergoes photooxidation. Cytocrome c photooxidation is attenuated to zero in two 1-electron steps with Em of +30 mV and ?130 mVPossible roles for +30 mV and ?130 mV components in photosynthetic electron transport in Chlorobium are discussed. |
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