The Electronic properties of cytochrome c iron related to its reactions

Abstract

The aim of this thesis was to explore the possibility of understanding the reactions of biological molecules in terms of modern inorganic chemical theory In particular, cytochrome c and the interaction of protein and iron electronic properties were chosen for study. Experimental inorganic techniques investigated were magnetic susceptibility, E.S.R., Mössbauer, N.M.R. and electronic absorption spectroscopy. The latter technique appeared most promising and experimental, theoretical and comparative analysis studies made use of this technique and its theory. In all techniques the complexity of the structure hampered detection or interpretation of results. Only in such an exceptional case as the heme electronic absorption α, β and γ bands, can experimental observation be confined to the effects of reactions of the molecule on a simpler structure. Although these heme bands were found to be remarkably insensitive to the properties of the molecule as a whole, study of the change on oxidation yielded information on the nature of protein-iron interactions which are probably significant to the biological reaction. The protein was found to control the iron active centre on auto-oxidation. Combined experimental, theoretical and comparative studies gave a strong indication that this change in oxidisability of the iron occurs on interaction of the protein with large charged molecules causing protein conformation change and hence alteration of the iron electronic properties through increasing the fifth and/or sixth ligand distance from the iron. Such a mechanism would abolish the crevice model of the protein function being steric interference to oxygen and provide an important role for the protein in biological reactions.