A new soluble 10Â kDa monoheme cytochrome c-552 from the anammox bacterium Candidatus “Kuenenia stuttgartiensis”

The chemolithoautotrophic anammox bacterium Candidatus “Kuenenia stuttgartiensis” grows anaerobically using ammonium as electron donor for nitrite reduction. More than 10% of the proteins in cell extracts of “K. stuttgartiensis” consist of c-type heme proteins. A 10 kDa soluble cytochrome c was purified from cell extracts using ultracentrifugation and anion exchange chromatography. The UV/Vis spectrum of the reduced cytochrome showed the γ, β and α absorption maxima at 419, 522 and 552 nm, respectively. The N-terminal amino acid sequence and peptide fragments of the tryptic digest of the protein were used to identify the corresponding gene. Analysis of the gene product showed that the protein was preceded by a 30 amino acids long leader sequence and that it belonged to the low-spin class ID cytochrome c. The CXXCH motive was located at the N-terminal site of the protein. The gene organization of the cytochrome showed some resemblance to cytochrome c clusters of unknown function in the genome of Nitrosomonas europaea and Geobacter sulfurreducens PCA.