Study of Redox Potential in Cytochrome c Covalently Bound to Terminal Oxidase of Alkaliphilic Bacillus pseudofirmus FTU

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M. S. Muntyan^1* and D. A. Bloch²

¹Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia; fax: (495) 939-3181; E-mail: muntyan@genebee.msu.su

²Institute of Biotechnology, University of Helsinki, P. O. Box 65, 00014 Helsinki, Finland; E-mail: dmitry.bloch@helsinki.fi

^* To whom correspondence should be addressed.

Received July 6, 2007; Revision received July 25, 2007

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Spectroelectrochemistry was used to determine the midpoint redox potentials of heme cofactors of the caa₃-type cytochrome oxidase from the alkaliphilic bacterium Bacillus pseudofirmus FTU. The apparent midpoint potentials (E_m^app) for the most prominent transitions of hemes a and a₃ (+193 and +334 mV, respectively) were found to be similar to the values reported for other enzymes with high homology to the caa₃-type oxidase. In contrast, the midpoint potential of the covalently bound cytochrome c (+89 mV) was 150-170 mV lower than in cytochromes c, either low molecular weight or covalently bound to the caa₃ complex in all known aerobic neutralophilic and thermo-neutralophilic bacteria. Such an unusually low redox potential of the covalently bound cytochrome c of the caa₃-type oxidase of alkaliphilic bacteria, together with high redox potentials of hemes a and a₃, ensures more than twice higher difference in redox potentials inside the respiratory complex compared to the homologous mitochondrial enzyme. The energy released during this redox transition might be stored in the transmembrane H⁺ gradient even under low Deltap in the alkaline environment of the bacteria at the expense of a significant increase in DeltaG of the coupled redox reaction.

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KEY WORDS: Bacillus pseudofirmus, alkaliphile, cytochrome c, caa₃, cytochrome oxidase, redox potential

DOI: 10.1134/S0006297908010161

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