CW-EPR and ENDOR Study of Cytochrome c6 from Anabaena PCC 7119

The detailed analysis of the continuous-wave electron paramagnetic resonance and electron nuclear double resonance measurements on cytochrome c6 from Anabaena PCC7119 reveals several electronic and structural properties of this hemeprotein. The oxidized protein shows two forms that differ in the arrangement of the residues that act as heme axial ligands. Information about the orientation of these residues is obtained for one of the forms, which turns out to differ from that found in the reduced protein from x-ray experiments. The biological significance of these results is discussed.