Collect. Czech. Chem. Commun. 2006, 71, 1627-1641

Conformational Transitions of Ferricytochrome c in Strong Inorganic Acids

Marek Stupáka, Jaroslava Bágeľováb, Diana Fedunováb and Marián Antalíkb,c,*

a Department of Medical Chemistry and Biochemistry, Faculty of Medicine, P. J. Šafárik University, Tr. SNP 1, 040 66 Košice, Slovak Republic
b Department of Biophysics, Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Košice, Slovak Republic
c Institute of Chemistry, Department of Biochemistry, Faculty of Sciences, P. J. Šafárik University, Moyzesova 11, 040 01 Košice, Slovak Republic


Conformational transitions of horse heart ferricytochrome c (ferricyt c) have been investigated in the presence of strong inorganic acids and their salts by optical absorption spectroscopy, magnetic circular dichroism and circular dichroism. In the presence of acids (HClO4 or H2SO4, pH 2) or their salts (1 M NaClO4 or Na2SO4, pH 2, 25 °C), the three ligation states of ferricyt c heme were identified. One is the high-spin state: His18-Fe-H2O (40-50%), and two are the low-spin states: His18-Fe-Met80 (30-25%) and His18-Fe-His (30-25%). Under these conditions low temperatures facilitate native heme coordination of ferricyt c. Transition from low-spin to high-spin heme coordination of ferricyt c is complete in 1 M HClO4 or 3 M H2SO4. At the concentration of HClO4 and H2SO4 above 3 M, different behavior in spectral transitions of ferricyt c near the heme is observed. High-spin pentacoordinated ferricyt c with the heme ligand of His18-Fe is formed in 8 M H2SO4. This state is unstable at higher concentration of H2SO4 and porphyrin ferricyt c is formed. At HClO4 concentration higher than 3 M, the new, until this time not observed heme coordination structure of ferricyt c originates.

Keywords: Protein structure; Ferricytochrome c; Heme ligands; Conformational transitions; Absorption spectroscopy; MCD; CD.

References: 35 live references.