Energy-transducing membranes proton transport

Ubiquinones are energy transducers that are obligatory in many respiratory and photosynthetic electron transport chains. The ubiquinone enzymes involved in these reactions usually function in a manner that couples the electron transfer by the ubiquinone to proton translocation across the membrane.The structural makeup of the ubiquinone active site permits varying functional roles that influence the electron and proton chemistry. 

Energy derived from electron transport in mitochondrial, chloroplast thylakoids and bacterial plasma membranes is transduced to form ATP by the Fi-Fq proton translocating ATP synthases. These enzyme complexes are composed of an intrinsic membrane protein complex, Fq, which mediates H+-translocation, and a peripheral protein complex, Fi, which catalyzes the terminal step of synthesis of ATP from ADP and Pi. 

Energy-transducing processes in the cytoplasmic membrane of Rps. sphaeroides such as electron-transfer-linked proton translocation, and solute transport can be studied in whole cells or in isolated membrane vesicles wnich have retained their functional properties. In these latter systems the membrane-bound activities can be separated from activities in the cytoplasm. Two procedures have been described for the isolation of membrane vesicles. Mechanical disruption of the cells by sonication. French-press treatment or grinding with aluminium yields so-called chromatophores which are mainly derived from the intracytoplasmic membranes (Oelze, Drews, 1972). 

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