Studies on the undecapeptide of ferricytochrome c using ESR, Mössbauer and visible spectroscopies.

The ESR, Mössbauer, and visible spectra of the undecapeptide of ferricytochrome c (HPp) were measured for both the solid peptide and solutions of the peptide at pH 1.5, 7, and 10. At the low pH, the iron exists in the HPp in the high-spin species. At neutral and alkaline pHs, the low-spin ferric species predominate. The results of these measurements support the previous suggestions concerning the ligands in the fifth and sixth position of HPp at the neutral and alkaline pHs. The spectra of lyophilized preparations of HPp show the presence of both high and low-spin ferric species. The study of the Mössbauer spectra of the lyohilized preparations as function of temperature shows that there exists a spin-spin equilibrium between the two spin states. The relative amounts of the two components vary with the preparation. In these preparations there exist two components, one of which exists in the equilibrium mixture and the second in the high-spin form.