Abstract: The solution structure of the imidazole adduct of oxidized horse heart cytochrome c(Im-cyt c) has been determined through 2D NMRspectroscopy. The 35 conformers of the family show the RMSDvalues to the average structure of 0.063±0.007 nm for the backbone and 0.107±0.007 nm for all heavy atoms, respectively. The secondary structure elements and the overall folding of the present structure are substantially similar to those of the solution structure of native protein. However, the replacement of the axial ligand Met 80 with the exogenous imidazole ligand induces significant conformation changes in both backbone and side chains of the residues locating in the distal axial ligand regions. The electron delocalization on the heme moiety and the magnetic susceptibility tensor are consistent with these structural features.

Key words: Cytochrome c, NMR, Solution structure, Electronic structure