Abstract: The secondary structures of native cytochrome c(cyt c) in both solid and solution states and four platinum modified cyt c derivatives in solution were determined by means of Fourier transform infrared spectroscopy. It was found that the secondary structure of cyt c in solid state is similar to that in the solution. In the cases of platinum-modified cyt c derivatives, when the binding sites of platinum complex are on or near the surface of the protein, its secondary structure is similar to that of native cyt c. However, when the platinum complex binds to Met 80 ligand and causes the replacement of the second axial ligand by non-native Lys 79 ligand or H₂O supplied by solvent, there is a significant difference between the structures of low-or high-spin state cyt c derivatives and that of native cyt c. The results suggest that axial ligand Met 80 residue plays an important role in stabilizing the secondary structure of cyt c.

Key words: Cytochrome c, Platinum, Secondary structure, FT IR