Studies on the Undecapeptide of Ferricytochrome c Using ESR, Mössbauer and Visible Spectroscopies

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Abstract
The ESR, Moessbauer and visible spectra of the undecapeptide of [horse heart] 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 Fe exists in the HPp in the high-spin species. At neutral and alkaline pHs, the low-spin ferric species predominate. These results support previous suggestions concerning the ligands in the 5th and 6th position of HPp at 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 Moessbauer spectra of the lyophilized preparations as function of temperature shows that a spin-spin equilibrium exists between the 2 spin states. The relative amounts of the 2 components vary with the preparation. These preparations contain 2 components, 1 of which exists in the equilibrium mixture and the 2nd in the high-spin form.

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