Cytochrome c reconstituted from two peptide fragments displays native‐like redox properties

Recombination of two fragments of horse cytochrome  c (the heme‐containing N‐fragment, residues 1–56, and the C‐fragment, residues 57–104), which are substantially unstructured at neutral pH, gives rise to a 1 : 1 fragment complex with a compact conformation, in which the α helical structure and the native Met80–Fe(III) axial bond are recovered. With respect to the native protein, the ferric complex shows a less rigid atomic packing and a decreased stability [Δ(Δ G o ) D  = 14.7 kJ·mol −1 ], ascribed to perturbations involving the Trp59 microenvironment and, to a lower extent, the heme pocket region. The redox potential, E 1/2  = 234 ± 5 mV vs. normal hydrogen electrode at 25 °C, is close to that of the intact protein, consistent with recovery of the native Met80–heme Fe(III) axial bond. Furthermore, the fragment complex shows reactivity similar to intact cytochrome  c , in the reaction with cytochrome  c oxidase. We conclude that the absence in the complex of some native cross‐links and interlocked packing important for protein rigidity and stability is not as relevant for maintaining the native redox properties of the protein, provided that some structural requirements (i.e. recovering of the native‐like α helical structure) are fulfilled and coordination of Met80 to the heme‐iron is restored.