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 ( p K a = 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 P i, 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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