title: Characterization of a quinole-oxidase activity in crude extracts of Thermoplasma acidophilum and isolation of an 18-kDa cytochrome.
abstract: A quinol-oxidase activity was detected in crude extracts of the thermoacidophilic archaebacterium Thermoplasma acidophilum. The activity was optimal at pH 5.4 and 50 degrees C. The Km for ubiquinol-10 was 18 microM. The enzyme was inhibited by 2n-heptyl-4-hydroxyquinoline N-oxide with a Ki of 150 nM. Ubiquinols with different side-chain lengths were oxidized at similar rates, whereas menaquinols were converted at 6-12-fold higher rates compared to ubiquinols. Membranes from T. acidophilum contain cytochromes of b, d and a1 types, as shown by optical spectroscopy. CO difference spectroscopy suggests the existence of a cytochrome o. A b-type cytochrome with an apparent molecular mass of 18 kDa was purified in the presence of high detergent concentrations. It readily forms dimers on SDS/PAGE. This cytochrome also contains Cu, as shown by atomic-absorption spectroscopy. Redox titration suggests that the 18-kDa cytochrome may contain 2 heme groups; b558 with a midpoint potential of 75 mV and b562/553 with a midpoint potential of -150 mV.
authors.affiliation: Max-Planck-Institut für Biophysik, Frankfurt am Main, Federal Republic of Germany.
authors.forename: P
authors.initials: P
authors.lastname: Gärtner
mesh_terms: D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D003573:Cytochrome b Group / Q000302:isolation & purification*; D004591:Electrophoresis, Polyacrylamide Gel; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D006912:Hydroxyquinolines; D007700:Kinetics; D008970:Molecular Weight; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013379:Substrate Specificity; D013696:Temperature; D013822:Thermoplasma / Q000201:enzymology*; D014451:Ubiquinone / Q000378:metabolism* / Q000031:analogs & derivatives; D014812:Vitamin K / Q000031:analogs & derivatives / Q000378:metabolism; D024482:Vitamin K 2 / Q000031:analogs & derivatives*
chemical_list: D003573:Cytochrome b Group; D006912:Hydroxyquinolines; D024482:Vitamin K 2; D014812:Vitamin K; D014451:Ubiquinone; C001333:2-(n-heptyl)-4-hydroxyquinoline N-oxide; C062629:menaquinone 7; D010088:Oxidoreductases; C020094:duroquinol oxidase; C003741:ubiquinol