title: Correlation of acid-induced conformational transition of ferricytochrome c with cyanide binding kinetics.
abstract: A relation between pH-induced conformational transitions of horse heart ferricytochrome c and the kinetics of external ligand coordination to heme iron was investigated by optical spectroscopy, circular dichroism and viscometry. The dependencies of both the association, k (a), and dissociation rate constants of cyanide binding on pH were determined from kinetic measurements. The association rate constant exhibits a bell-shaped form of dependence on pH in the region where this protein unfolds. The maximum of the dependence of k (a) on pH is found to be coincident with the pK values of conformational transitions of ferricytochrome c in solutions with both low and high ionic strengths. This observation is explained in terms of ferricytochrome c unfolding, which is characterized by two processes: the gradual opening of the heme crevice accompanied by the detachment of the axial Met80 and its replacement with a water molecule. The former process enhances the rate, whereas the latter results in the inhibition of the rate of cyanide binding.
authors.affiliation: Department of Biochemistry, Faculty of Science, P. J. Safárik University, Moyzesova 11, 04001, Kosice, Slovakia. rastislav.varhac@upjs.sk
authors.forename: Rastislav
authors.initials: R
authors.lastname: Varhac
authors.forename: Marián
authors.initials: M
authors.lastname: Antalík
mesh_terms: D000143:Acids / Q000737:chemistry; D000818:Animals; D002942:Circular Dichroism; D003486:Cyanides / Q000378:metabolism*; D045304:Cytochromes c / Q000737:chemistry*; D006418:Heme / Q000737:chemistry; D006736:Horses; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D009206:Myocardium / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D013056:Spectrophotometry, Ultraviolet; D014783:Viscosity
chemical_list: D000143:Acids; D003486:Cyanides; D006418:Heme; D045304:Cytochromes c; D007501:Iron