A new class of bacterial multi-subunit membrane-bound electron transfer complexes has been identified based on biochemical and bioinformatic data (7). It contains seven subunits, two of which are c-type cytochromes. The complex was purified from Chloroflexus aurantiacus, and putative operons for similar complexes were also identified in a wide range of nonphotosynthetic bacteria. In most cases, the presence of the new complex is anticorrelated with the cytochrome bc or bf electron transfer complex, suggesting that it replaces it functionally (Fig. 4). This appears to be a widespread yet previously unrecognized complex involved in energy metabolism in bacteria. Additional characterization of redox properties and proton pumping activities of this complex is underway (8).
