NMR investigations of the Rieske protein from thermus thermophilus support a coupled proton and electron transfer mechanism

NMR spectroscopy is used to determine the the p[K.sub.a] values of each of the imidazole rings of the two ligating histidines (His134 and His154) in the oxidized and reduced states of the Rieske protein from Thermus thermophilus (TtRp). The likely translocation of TtRp between the cytochrome b and cytochrome c sites is most consistent with a mechanism involving the coupled transfer of an electron and transfer of the proton across the hydrogen bond between the hydroquinone and His154 at the cytochrome b site.