title: Role of quinones in the branch of the Escherichia coli respiratory chain that terminates in cytochrome o.
abstract: The role of quinones in the cytochrome o branch of the Escherichia coli respiratory chain was investigated by using mutant strains lacking the cytochrome d terminal oxidase complex. The only cytochromes present were cytochrome b556 and the cytochrome o complex, consisting of cytochrome b555-b562. Mutant strains missing ubiquinone, menaquinone, or both were constructed in the cytochrome d-minus (cyd) background. The steady-state levels of cytochrome b reduction were examined and compared in these strains to assess the effects of the quinone deficiencies. The data clearly show that a ubiquinone deficiency results in a lower level of cytochrome b reduction in the steady state. The data are consistent with a simple model in which ubiquinone is placed on the dehydrogenase side of all the cytochromes in this branch of the respiratory chain. There is no evidence from these experiments for a role of quinones in the respiratory chain at any site besides this one.
mesh_terms: D003573:Cytochrome b Group / Q000378:metabolism; D017937:Cytochrome d Group; D003580:Cytochromes / Q000378:metabolism*; D045222:Electron Transport Chain Complex Proteins; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins; D009154:Mutation; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D011809:Quinones / Q000378:metabolism*
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D045222:Electron Transport Chain Complex Proteins; D029968:Escherichia coli Proteins; D011809:Quinones; D017937:Cytochrome d Group; C017168:cytochrome bo, E coli; D010088:Oxidoreductases; C040077:cytochrome bd terminal oxidase complex, E coli; D010100:Oxygen