A ba3 oxygen reductase from the thermohalophilic bacterium Rhodothermus marinus |
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Authors: | Veríssimo Andreia F Pereira Manuela M Melo Ana M P Hreggvidsson Gudmundur O Kristjansson Jakob Kr Teixeira Miguel |
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Affiliation: | Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal. |
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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. |
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Keywords: | terminal oxidase cytochrome ba3 cytochrome oxidase redox titration |
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