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PubMed1979

Factors controlling the binding of two protons per electron transferred through the ubiquinone and cytochrome b/c2 segment of Rhodopseudomonas sphaeroides chromatophores.

1. On every turnover, 2.0 protons can be bound by the membrane for each single electron moving through the Q-b/c2 oxidoreductase. 2. One proton (H+II) binding reaction is, and one (H+I) is not, sensitive to antimycin. 3. The redox states of electron transfer components other than the proton binding agents can affect both the rate of proton uptake and the apparent pK values on the agents binding the protons. 4. The presence of valinomycin under certain well-defined conditions can strongly influence the value of the measured pK on the H+II binding agent.

Bacterial Chromatophores↗
PubMed1992

Determination of the position of the Qi.- quinone binding site from the protein surface of the cytochrome bc1 complex in Rhodobacter capsulates chromatophores.

The technique of distance measurement, utilizing spin relaxation enhancement by an external probe, has been extended to the study of intrinsic semiquinone radicals through the use of holmium-EDTA complexes and continuous wave electron paramagnetic resonance spectroscopy. This technique has been used to determine the distance of the semiquinone anion, Qi (also designated as Qn.- or Qc.-), from the surface of the ubiquinone cytochrome c oxidoreductase, consisting of only three subunits, in membrane particles from Rhodobacter capsulates. The location of the semiquinone anion is 6-10 A from the N side protein, establishing that there are two separate quinone reaction sites, i.e., 'Qi' and 'Qo', within this complex on opposite sides of the membrane. The results are discussed in relation to reported ENDOR, EPR, and optical studies of the mitochondrial counterpart.

Bacterial Chromatophores↗