Membrane-bound electron transfer chain of the thermohalophilic bacterium Rhodothermus marinus: a novel multihemic cytochrome bc, a new complex III

Biochemistry. 1999 Jan 26;38(4):1268-75. doi: 10.1021/bi9818063.


A novel multihemic cytochrome bc complex was isolated from the membranes of Rhodothermus marinus. It is a complex with a minimum of three subunits (43, 27, and 18 kDa), containing five low-spin heme centers of the B and C types, in a 1:4 ratio. All the C-type hemes are in the same subunit (27 kDa). Three distinct redox transitions, at 235, 80, and -45 mV, were observed by visible redox titrations. The first involves one B- and one C-type hemes, and in the other two transitions one and two C-type hemes are involved, respectively. Spectroscopic data strongly suggest that the two hemes intervening in the last transition are in van der Waals contact, yielding a split Soret band. Electron paramagnetic resonance spectra of the oxidized complex show resonances of five low-spin ferric heme centers. Upon reduction with ascorbate, all these resonances vanish and a new one attributed to the last pair of hemes appears. A [3Fe-4S]1+/0 center copurifies with this complex, having a high reduction potential of +140 mV. No Rieske-type centers are detected in R. marinus and no effect is observed in the respiratory rates when the typical bc1 complex inhibitors are present, suggesting that such a complex is absent in R. marinus [Pereira et al. (1994) FEBS Lett. 352, 327-330]. The newly isolated cytochrome bc complex has quinol:cytochrome c or high-potential iron-sulfur protein (HiPIP) oxidoreductase activity, being a functional analogue of the canonical bc1 complexes; i.e., it is the complex III in R. marinus. This complex plays a central role in this bacterium's electron-transfer chain, coupling the electron transfer between the quinols reduced by the dehydrogenases and the HiPIP, the final electron donor to the terminal oxidases [Pereira, M. M., Carita, J. N., and Teixeira, M. (1999) Biochemistry 38, 1276-1283].

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / metabolism
  • Cell Membrane / metabolism
  • Cytochrome b Group / chemistry
  • Cytochrome b Group / isolation & purification
  • Cytochrome b Group / metabolism*
  • Cytochrome c Group / chemistry
  • Cytochrome c Group / isolation & purification
  • Cytochrome c Group / metabolism*
  • Electron Spin Resonance Spectroscopy
  • Electron Transport
  • Electron Transport Complex III / chemistry
  • Electron Transport Complex III / isolation & purification
  • Electron Transport Complex III / metabolism*
  • Gram-Negative Aerobic Bacteria / metabolism*
  • Heme / metabolism
  • Iron-Sulfur Proteins / metabolism
  • Macromolecular Substances
  • Oxidation-Reduction
  • Photosynthetic Reaction Center Complex Proteins*
  • Spectrophotometry


  • Bacterial Proteins
  • Cytochrome b Group
  • Cytochrome c Group
  • Iron-Sulfur Proteins
  • Macromolecular Substances
  • Photosynthetic Reaction Center Complex Proteins
  • high potential iron-sulfur protein
  • Heme
  • Electron Transport Complex III