Coupling between redox and acid-base energy by cytochrome b-564 in Baker's yeast mitochondria |
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Authors: | M Hervás F F de la Rosa M A de la Rosa M Losada |
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Institution: | Departamento de Bioquímica, Facultad de Biología y C.S.I.C., Universidad de Sevilla, Apdo. 1095, Sevilla, Spain |
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Abstract: | Baker's yeast mitochondrial cytochrome b-564 is characterized by exhibiting both a labile pH-independent high-potential form (E'o, pH 7 = + 190 mV) and a stable pH-dependent (pKa = 6.8) low-potential form (E'o, pH 7 = + 70 mV). The different behavior of these two forms of cytochrome b-564 versus pH seems to be a decisive factor for transduction of redox energy into acid-base energy in oxidative phosphorylation site 2. Deenergizing treatments, such as ADP plus Pi, result in the conversion of all the mitochondrial cytochrome b-564 into its low-potential form, whereas energization with ATP specifically transforms the cytochrome into its high-potential form, the ATP effect being neutralized by the ATPase inhibitor oligomycin and by the uncoupler FCCP. Accordingly, a minimal model for coupling between redox energy and acid-base energy through an electronically energized and protonated ferricytochrome b-564 intermediate is proposed. The energy-transducing properties of mitochondrial cytochrome b-564 seems to be shared by chloroplast cytochrome b-559. |
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Keywords: | CCCP EDTA ethylenediaminetetraacetate FCCP |
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