MECHANISM OF DENATURATION OF CYTOCHROME-C BY LITHIUM-SALTS

Guanidine hydrochloride, LiCl and LiBr denaturations of cytochrome-c have been followed by observing changes in difference spectral intensities in the visible and UV regions and by circular dichroism. It has been observed that the former induces a highly cooperative and reversible transition between the native and denatured conformations. On the other hand, lithium salts induce a three-state transition in the protein. Characterization of the native state, X (intermediate) state and the end products by measurements of all optical properties and intrinsic viscosity suggests (i) that in each denaturant the end product is a random coil, and (ii) that the X state corresponds to a highly folded conformation in which heme seems to be completely exposed to the solvent. It has been observed that the second transition induced by the action of lithium salts corresponds to the unfolding of the polypeptide backbone. Measurements of the free energy change associated with all transitions suggest that protein polypeptide chain cannot exist in the folded conformation without the interaction between heme and globin.