Extended x-ray absorption fine structure (EXAFS) studies of cytochromes c: structural aspects of oxidation-reduction

Abstract

EXAFS fluorescence spectra were recorded for high-potential c-type cytochromes which range in oxidation-reduction potential from +145 to +365 mV. No average Fe-ligand bond length differences greater than 0.03 A were observed, for any cytochrome source of oxidation state. Least-squares analysis in combination with model calculations allowed limits to be set on the average Fe-N bond length (1.97-1.99 A) and the Fe-S bond length (2.29-2.32 A). A change of 0.05 A in either the average Fe-N or the Fe-S bond length is readily detectable with the range and quality of the data presented here. Two major conclusions are drawn from this study: In octahedrally coordinated iron porphyrin systems, Fe-N and Fe-S bond lengths are independent of oxidation-reduction potential, and they are also independent of oxidation state. A model for the regulation of oxidation-reduction potential in cytochrome c is proposed.

Detecting transient protein–protein interactions by X‐ray absorption spectroscopy: The cytochrome c6‐photosystem I complex

“…From the analysis of the fitting parameters shown in Table 1, it is apparent that there are no significant changes in the short range structure around the metal centre of Cc 6 when it binds to PSI Hg , independently of the oxidation state and as previously described for other c-type cytochromes [4,5,17]. However, a slight increase in the Fe-S distances can be observed when the cytochrome forms a complex with PSI Hg in the oxidized and reduced forms.…”

“…Early comparative XAS studies on isolated c-type cytochromes have shown that the heme co-ordination geometry is highly conserved, independently of its redox state [4,5]. However, no data has been reported with regard to the changes in the heme moiety upon binding of a cytochrome to its targets.…”

Amino acid sequence, haem-iron co-ordination geometry and functional properties of mitochondrial and bacterial c-type cytochromes

“…However, the variations in redox potentials between different species (Table 2) cannot be rationalized with any of these hypotheses. The available data on c-type cytochrome structures do not conclusively support any of the proposed theories and are, in most cases, even contradictory (Korszun & Salemme, 1977;Fiechtner & Kassner, 1978;Pettigrew et al 1978;Mashiko et al 1981;Takano & Dickerson, 1981a;Korszun et al 1982). Experimental results from the comparative structural studies of the active site conformation in c-type cytochromes indicate a possible control mechanism for the redox properties in extreme low redox potential Desulfovibrio cytochromes c-553.…”

Statistical strategy for stereospecific hydrogen NMR assignments: Validation procedures for the floating prochirality method

“…Constraints of 1 ]k breadth were also applied between the heme iron and its two ligands. These constraints were centered about the distances determined by solution state EXAFS (Korszun et al, 1982(Korszun et al, , 1989. The final constraint set used here comprised approximately 13 NOE distance bounds per residue.…”