Extinction coefficients and midpoint potentials of cytochrome c₆ from the cyanobacteria Arthrospira maxima, Microcystis aeruginosa, and Synechocystis 6803

Cytochrome c₆ is a soluble heme protein that serves as a photosynthetic electron transport component in cyanobacteria and algae, carrying electrons from the cytochrome bf complex to photosystem I. The rapid accumulation of cytochrome c₆ sequence data from a wide range of species, combined with significant advances in determining high resolution three-dimensional structures, provides a powerful database for investigating the relationship between structure and function. The fact that the gene encoding cytochrome c₆ can be readily modified in a number of species adds to the usefulness of cytochrome c₆ as a tool for comparative analysis. Efforts to relate cytochrome c₆ sequence information to structure, and structural information to function depend on knowledge of the physical and thermodynamic properties of the cytochrome from different species. To this end we have determined the optical extinction coefficient, the oxidation/reduction midpoint potential, and the pH dependence of the midpoint potential of cytochrome c₆ isolated from three cyanobacteria, Arthrospira maxima, Microcystis aeruginosa, and Synechocystis 6803. Copyright (C) 1999 Elsevier Science B.V.