Reevaluation of the redox and redox-Bohr cooperativity in tetrahaem Desulfovibrio vulgaris (Miyazaki F) cytochrome c 3

Abstract

The thermodynamic model of five interacting charge centres (four haems and an ionisable centre), which was used in the characterisation of the thermodynamic properties of Desulfovibrio vulgaris (Hildenborough) cytochrome c3 (c3DvH), is now used to reevaluate the thermodynamic properties in Desulfovibrio vulgaris (Miyazaki F) cytochrome c3 (c3DvM) on the basis of published data (Park, J.-S., Ohmura, T., Kano, K., Sagara, T., Niki, K., Kyogoku, Y. and Akutsu, H. (1996) Biochim. Biophys. Acta 1293, 45–54). Contrary to the assertion of Park et al. (1996), the pH dependence of the proton chemical shifts of haem methyls in c3DvM in several stages of oxidation is well described by the model, which involves both homotropic (e–/e–) and heterotropic (e–/H+) cooperativity. This shows that the pH dependence observed for c3DvM is not significantly more complicated than that observed for c3DvH. Since the parameters which we now obtain for c3DvM are generated with the same model as those from c3DvH, albeit using less precise data, it is possible to make a preliminary comparison of the thermodynamic properties of these two proteins and of their role in energy transduction.