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

Abstract

Undecapeptide of Ferricytochrome c, Electron Spin Resonance, Mössbauer Spectroscopy, Visible Spectroscopy The ESR, Mössbauer, and visible spectra of the undecapeptide of ferricytochrome c (H P p) 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 H Pp 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 temerature 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.

Microperoxidase-11: Molecular Dynamics and Q-Band Excited Resonance Raman of the Oxidized, Reduced and Carbonyl Forms

“…In the ferric species, the presence of 6-coordinate iron has been proposed with two possible spin states: at pH< 7, HS Fe3+ with his18 as 5th ligand and a water as 6th ligand, and at pH -7-11, LS Fe3+ with a stronger field 6th ligand, such as valll or lys13 of a second MP11 aggregated molecule (13). This LS Fe3+ assignment at neutral pH was confirmed by other workers (14) but is inconsistent with reports concluding that MPII is present in two spin states in the neutral pH range (15,16). Finally, the helical arrangement of the polypeptide has also been inconsistently described as a random coil ( 11) and as maintaining the helical structure which it has in the parent cytochrome (12,13).…”

“…Cys 14 and cys 17 provide the sulfurs for the thioether linkages and the imidazole ofhis18 is coordinated to the iron as a fifth ligand (10) (Figure 1). No xray structure has been determined but the undecapeptide has been characterized by visible optical spectroscopy, circular dichroism (8,9,11,12), NMR (13) and Moessbauer (14)(15)(16). These studies have shown that MPll is monomeric at acid pH and polymeric at alkaline pH, the state of aggregation being dispersed however, by coordination of the iron to a sixth ligand or by dilution to the mM range (8).…”

Mössbauer studies on LaNi4.7Sn0.3 and its hydride

“…10 Samples were mounted in polypropylene holders. Particle size deteml.inations were performed using all lSI SS40 scanning d(~ctron microscope and standard amtly~is methods.…”