The effects of imidazole binding on the conformation of cytochrome c.

Many individual protons exhibit different chemical shifts in Im-cyt c and cyt c, reflecting diamagnetic shift effects as a result of structure change, and in addition contact and pseudocontact shifts that occur only in the paramagnetic oxidized form. To estimate the chemical shift differences caused by structure change, we removed the pseudocontact shift contribution. The anisotropy and direction of the magnetic susceptibility anisotropy tensor were determined. There was evidence for conformational changes induced by the breakage of Fe-S bond. It was concluded that the Im-cyt c had undergone a rearrangement of several regions forming the heme pocket of the protein. The hydrogen-bond network in the heme cavity was affected by the substitution.