LINKED FUNCTIONS IN HEME SYSTEMS: OXIDATION-REDUCTION POTENTIALS AND ABSORPTION SPECTRA OF A HEME PEPTIDE OBTAINED UPON PEPTIC HYDROLYSIS OF CYTOCHROME C

Abstract

Studies are reported of the oxidation-linked proton functions of a heme undecapeptide obtained upon peptic hydrolysis of beef-heart cytochrome c. Oxidation-reduction potentials of the heme peptide in solutions containing imidazole were measured over the range of pH 4 to 13. The potentials observed differ greatly from the corresponding ones reported for cytochrome c, and resemble more nearly those found for horseradish peroxidase. The oxdiation-reduction potential of the imidazole-heme peptide system (ferri-ferro) at pH 7 and 30[degree] is -0.195 volt. The variation of potential with pH indicates oxidation-linked proton functions with the following pK[image] values: oxidized form, 6.6, 10.5, and 11.1; reduced form, 4.6, 5.6, 7.2, and 9.8. Conditions were determined under which various solutions of the heme peptide appear free of irreversible effects, and the variation with pH of the absorption spectra displayed under such conditions was examined for both the oxidized and reduced forms of the heme peptide. The relationship between the spectrophotometric observations and the oxidation-reduction data has been considered, and has formed a basis for discussion of the processes reflected in the experimental results reported.