Characterization of the dihemic cytochrome C549 from the marine denitrifying bacterium Pseudomonas nautica 617

Abstract A dihemic ferricytochrome c 549 (21 kDa) was purified and characterized from cells of the marine denitrifier Pseudomonas nautica strain 617. Several spectroscopic techniques, including UV-visible, NMR and EPR spectroscopies were applied to the characterization of this cytochrome. The visible and the 1 H-NMR spectra show that both hemes have histidine-methionine as axial ligands. The dihemic cytochrome c 549 has mid-point redox potentials of +230 mV and +250 mV, at pH 7.6 and its NH 2 -terminal sequence presents a high degree of similarity with those of cytochromes c 4 . The EPR studies allowed the determination of the orientation between the two axial ligands, indicating an axial ligand field for one of the hemes of cytochrome c 549 and a rhombic symmetry for the other heme.