Multiheme e-type cytochromes from members of the Desulfbvibrionacea and Geobactereacea families play crucial roles in the bioenergetics of these microorganisms. Thermodynamic studies using NMR and visible spectroscopic techniques on tetraheme cytochromes c(3) isolated from Desulfbvibrio spp. and more recently on a triheme cytochrome from Geobacter sulfurreducens showed that the properties of each redox centre are modulated by the neighbouring redox centres enabling these proteins to perform energy transduction and thus contributing to cellular energy conservation. Electron/proton transfer coupling relies on redox-linked conformational changes that were addressed for some multiheme cytochromes from the comparison of protein structure of fully reduced and fully oxidised forms. In this work, we identify for the first time in a multiheme cytochrome the simultaneous presence of two different conformations in solution. This was achieved by probing the different oxidation stages of a triheme cytochrome isolated from G. sulfurreducens using 2D-NMR techniques. The results presented here will be the foundations to evaluate the modulation of the redox centres properties by conformational changes that occur during the reoxidation of a multiheme protein. (c) 2007 Elsevier Inc. All rights reserved.