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Ph variation of midpoint potential for 3 photosynthetic bacterial cytochromes c a link between physical and functional properties

Ph variation of midpoint potential for 3 photosynthetic bacterial cytochromes c a link between physical and functional properties

Biochimica et Biophysica Acta 679(3): 393-399

Midpoint redox potential (EM) vs. pH curves are reported over the pH range 5-10 for the cytochromes c' from 3 species of purple photosynthetic bacteria: Rhodospirillum rubrum, Rhodopseudomonas palustris and Chromatium vinosum. In each case, theoretical curves are fitted to the data and pK values for the reduced (pH 5-5.5) and oxidized (pH 8-8.5) forms of the protein are found to influence the midpoint redox potentials. The oxidized form pK values in each case correlate with previously determined pK value for variation in physical and/or spectroscopic properties. This correlation of functional and physical observables is discussed in terms of a possible mechanism of control of midpoint redox potential through heme iron-ligand bonding as moderated by the protein conformation in response to solution conditions. The reduced form pK values are discussed in terms of a mechanism which would alter the polarity of the heme environment, influencing redox potentials.

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