DIRECT ELECTROCHEMICAL EVIDENCE FOR AN EQUILIBRIUM INTERMEDIATE IN THE GUANIDINE-INDUCED UNFOLDING OF CYTOCHROME-C

This paper reports a voltammetric and spectroscopic investigation of t he guanidine-induced unfolding of cytochrome c at neutral pH and 25 de grees C. Electrochemical data provide direct evidence for the presence of an equilibrium intermediate (form I) strictly dependent on the den aturant concentration. The midpoint potential of farm I has been deter mined (E(1/2) = +0.010 V vs. NHE) and its structural features defined rom analysis of the circular dichroism and absorbance spectroscopy dat a obtained under the same experimental conditions. From the correlatio n of electrochemical and spectroscopic data, we propose that the featu res detected by the intermediate conform to the molten globule state.