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    The K-C channel in the cbb(3)-type respiratory oxygen reductase from rhodobacter capsulatus Is required for both chemical and pumped protons
    (Amer Soc Microbiology, 2014) Yıldız, Gülgez Gökçe; Gennis, Robert B.; Daldal, Fevzi; Öztürk, Mehmet
    The heme-copper superfamily of proton-pumping respiratory oxygen reductases are classified into three families (A, B, and C families) based on structural and phylogenetic analyses. Most studies have focused on the A family, which includes the eukaryotic mitochondrial cytochrome c oxidase as well as many bacterial homologues. Members of the C family, also called the cbb(3)-type oxygen reductases, are found only in prokaryotes and are of particular interest because of their presence in a number of human pathogens. All of the heme-copper oxygen reductases require proton-conducting channels to convey chemical protons to the active site for water formation and to convey pumped protons across the membrane. Previous work indicated that there is only one proton-conducting input channel (the K-C channel) present in the cbb(3)-type oxygen reductases, which, if correct, must be utilized by both chemical protons and pumped protons. In this work, the effects of mutations in the KC channel of the cbb(3)-type oxygen reductase from Rhodobacter capsulatus were investigated by expressing the mutants in a strain lacking other respiratory oxygen reductases. Proton pumping was evaluated by using intact cells, and catalytic oxygen reductase activity was measured in isolated membranes. Two mutations, N346M and Y374F, severely reduced catalytic activity, presumably by blocking the chemical protons required at the active site. One mutation, T272A, resulted in a substantially lower proton-pumping stoichiometry but did not inhibit oxygen reductase activity. These are the first experimental data in support of the postulate that pumped protons are taken up from the bacterial cytoplasm through the K-C channel.
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    Stoichiometry of proton pumping by the cbb(3)-type oxygen reductase in whole cells of Rhodobacter capsulatus at pH 7 is about 0.5 H+ per electron
    (Natl Acad Sciences, 2012) Murali, Ranjani; Yıldız, Gökçe Gülgez; Daldal, Fevzi; Gennis, Robert B.
    Recently, we reported (1) that the stoichiometry of proton pumping is about 0.4–0.5 proton per electron for members of the C family of respiratory oxygen reductases, also called the cbb3-type cytochrome c oxidases. This amount (0.5) is about half of the value obtained with the canonical A family of respiratory oxygen reductases, which includes the mitochondrial cytochrome c oxidases. We pointed out that the low stoichiometry correlates with the absence of the D channel for proton input and speculated that these properties may be an evolutionary adaptation to aerobic respiration under conditions of low oxygen.