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Results show that copperA-domain of cytochrome oxidase subunit II from Paracoccus denitrificans is Ph responsive exhibiting conformational changes at the copperA site with pH decrease. Data further indicate that the protein's conformational state is more stable at the 'low-pH' and the conformational transition is influenced by a slow deprotonation step.

A unique and enhanced strategy for purifying nitric oxide reductase (NOR) form membranes of Paracoccus denitrificans was developed. The purified enzyme was identified as a cytochrome bc complex which has two subunits in a 1:1 stoichiometry. The purified NorBC complex binds 0.87 g of dodecyl maltoside/g of protein and produces a dimer in solution. The NorB subunit resembles the primary catalytic subunit of cytochrome oxidase and is believed to contain the active bimetallic center in which two NO molecules are passed on to N2O.

In Paracoccus denitrificans the aa3-type cytochrome c oxidase and the bb3-type quinol oxidase have previously been characterized in detail, both biochemically and genetically. Here we report on the isolation of a genomic locus that harbours the gene cluster ccoNOQP, and demonstrate that it encodes an alternative cbb3-type cytochrome c oxidase. This oxidase has previously been shown to be specifically induced at low oxygen tensions, suggesting that its expression is controlled by an oxygen-sensing mechanism. This view is corroborated by the observation that the ccoNOQP gene cluster is preceded by a gene that encodes an FNR homologue and that its promoter region contains an FNR-binding motif. Biochemical and physiological analyses of a set of oxidase mutants revealed that, at least under the conditions tested, cytochromes aa3, bb3 and cbb3 make up the complete set of terminal oxidases in P. denitrificans. Protontranslocation measurements of these oxidase mutants indicate that all three oxidase types have the capacity to pump protons. Previously, however, we have reported decreased H+/e- coupling efficiencies of the cbb3-type oxidase under certain conditions. Sequence alignment suggests that many residues that have been proposed to constitute the chemical and pumped proton channels in cytochrome aa3 (and probably also in cytochrome bb3) are not conserved in cytochrome cbb3. It is concluded that the design of the proton pump in cytochrome cbb3 differs significantly from that in the other oxidase types. [ABSTRACT FROM AUTHOR]

A respiratory quinol oxidase complex that is encoded by the soxABCD operon has been purified from the thermoacidophilic archaeon Sulfolobus acidocaldarius. The enzyme was solubilized with dodecyl maltoside and purified in the presence of this detergent and ethylene glycol. The complex is hydrodynamically homogeneous and contains at least five different polypeptide. In addition to the major subunits SoxA, SoxB and SoxC, it has two small polypeptides. One of these is the translation product of a short open reading frame (now called the soxD gene) at the end of the operon. The optical and electron paramagnetic resonance spectra of the SoxABCD complex have been characterized, it probably contains four A-type haems which are bound to SoxB and SoxC. The structure of these haems is not identical to haem A. The novel haem Aa has a 2-hydroxyethyl geranylgeranyl in position 2 of the porphyrin ring whereas haem A has the related farnesyl-containing side-chain. [ABSTRACT FROM AUTHOR]