A Mössbauer study of ferri- and ferrocytochrome c

Applications of Mössbauer Spectroscopy in Biomedical Research

A brief review on the applications of Mössbauer spectroscopy in biomedical research discusses the results of more than fifty years of experience in this field. Basing on the numerous results the main directions of biomedical applications of Mössbauer spectroscopy are considered as follows: 1) studies of the quantitative changes of iron-containing biomolecules related to pathological processes; 2) studies of the qualitative changes in iron-containing biomolecules related to pathological processes; 3) studies of the effect of various environmental factors (physical, chemical, and biological) on iron-containing biomolecules; 4) studies of metabolic processes by means of analysis of the Mössbauer nuclides pathways in organisms; 5) studies of dynamic processes; 6) studies of pharmaceutical compounds and blood substitutes containing Mössbauer nuclides; 7) miscellaneous studies. Some examples of biomedical research using ⁵⁷Fe, ⁵⁷Co, ¹¹⁹Sn, ¹⁵³Sm, and ¹⁹⁷Au Mössbauer nuclides are presented.

Investigations of the low frequency modes of ferric cytochrome c using vibrational coherence spectroscopy

Femtosecond vibrational coherence spectroscopy is used to investigate the low frequency vibrational dynamics of the electron transfer heme protein, cytochrome c (cyt c). The vibrational coherence spectra of ferric cyt c have been measured as a function of excitation wavelength within the Soret band. Vibrational coherence spectra obtained with excitation between 412 and 421 nm display a strong mode at ∼44 cm^–1 that has been assigned to have a significant contribution from heme ruffling motion in the electronic ground state. This assignment is based partially on the presence of a large heme ruffling distortion in the normal coordinate structural decomposition (NSD) analysis of the X-ray crystal structures. When the excitation wavelength is moved into the ∼421–435 nm region, the transient absorption increases along with the relative intensity of two modes near ∼55 and 30 cm^–1. The intensity of the mode near 44 cm^–1 appears to minimize in this region and then recover (but with an opposite phase compared to the blue excitation) when the laser is tuned to 443 nm. These observations are consistent with the superposition of both ground and excited state coherence in the 421–435 nm region due to the excitation of a weak porphyrin-to-iron charge transfer (CT) state, which has a lifetime long enough to observe vibrational coherence. The mode near 55 cm^–1 is suggested to arise from ruffling in a transient CT state that has a less ruffled heme due to its iron d⁶ configuration.