Effect of heme iron valence state on the conformation of cytochrome c and its association witt membrane interfaces - A CD and EPR investigation

Recently cytochrome c has been mentioned as an important mediator in the ev ents of cellular oxidative stress and apoptosis, To investigate the influen ce of charged interfaces on the conformation of cytochrome c, the CD and ma gnetic circular dichroic behavior of ferric and ferrous cytochrome c in hom ogeneous medium and in phosphatidylcholine/phosphatidylethanolamine/cardiol ipin and dicetylphosphate liposomes was studied in the 300-600 and 200-320 nm wavelength region. EPR spectra demonstrate that the association of cytoc hrome c with membranes promotes alterations of the crystal field symmetry a nd spin state of the heme Fe3+. The studies also include the effect of P-i, NaCl, and CaCl2. Magnetic circular dichroism and CD results show that the interaction of both ferrous and ferric cytochrome c with charged interfaces promotes conformational changes in the cy-helix content, tertiary structur e, and heme iron spin state. Moreover, the association of cytochrome c with different liposomes is sensitive to the heme iron valence state. The more effective association with membranes occurs with ferrous cytochrome c. Dice tylphosphate liposomes, as a negatively charged membrane model, promoted a more pronounced conformational modification in the cytochrome c structure. A decrease in the lipid/protein association is detected in the presence of increasing amounts of CaCl2, NaCl, and P-i, in response to the increase of the ionic strength.