title: A ba3 oxygen reductase from the thermohalophilic bacterium Rhodothermus marinus.
abstract: The aerobic respiratory chain of the thermohalophilic bacterium Rhodothermus marinus has been extensively studied. In this study the isolation and characterization of a third oxygen reductase expressed in this organism are described. This newly isolated enzyme is a typical member of the type B family of haem-copper oxygen reductases, showing 43% amino acid sequence identity and 63% similarity with the ba3 oxygen reductase from Thermus thermophilus. It constitutes two subunits with apparent molecular masses of 42 and 38 kDa. It contains a low-spin B-type haem and a high-spin A-type haem. A stoichiometry of 1B: 1A haem per protein was obtained by spectral integration of UV-visible spectra. Metal analysis showed the presence of two iron and three copper ions, which is in agreement with the existence of a CuA centre. Taking advantage of having two spectroscopically distinct haems, the redox behaviour of the ba3 oxygen reductase was analysed and discussed in the framework of a model with interacting centres. Both haems, B and A, present two transitions, have unusually low reduction potentials of -65 mV and an interaction potential of -52.5 mV.
authors.affiliation: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal.
authors.forename: Andreia F
authors.initials: AF
authors.lastname: Veríssimo
authors.forename: Manuela M
authors.initials: MM
authors.lastname: Pereira
authors.forename: Ana M P
authors.initials: AM
authors.lastname: Melo
authors.forename: Gudmundur O
authors.initials: GO
authors.lastname: Hreggvidsson
authors.forename: Jakob Kr
authors.initials: JK
authors.lastname: Kristjansson
authors.forename: Miguel
authors.initials: M
authors.lastname: Teixeira
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000145:classification / Q000235:genetics; D003300:Copper / Q000737:chemistry; D006418:Heme / Q000737:chemistry; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000145:classification / Q000235:genetics; D045245:Rhodothermus / Q000201:enzymology* / Q000235:genetics; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein
chemical_list: D001426:Bacterial Proteins; D006418:Heme; D003300:Copper; D010088:Oxidoreductases