The oxidation—reduction potential of eukaryotic cytochromes c varies very little from species to species. We have introduced point mutations into isoform 1 of yeast cytochrome c (iso-1-cytochrome c) to selectively engineer a protein with a higher redox potential. Of the ten different mutant proteins generated for the present investigation Y67R, Y67K and W59H were found to be non-functional. Three other mutant proteins, L32M, L32T and T49K, were functional, but too unstable for biophysical studies. Mutant cytochromes c K79S, K79T, Y48H and Y48K were purified and characterized. The Y48K mutant is the only one that exhibits a significant increase of +117mV in redox potential compared with the wild-type protein while still supporting oxidative phosphorylation invivo. Low temperature difference spectroscopy confirmed the formation of the holoprotein, while adsorption and CD spectroscopy reveal perturbations in the structure of Y48K iso-1-cytochrome c.

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