title: Determination of the pK for the acid-induced denaturation of ferrocytochrome c.
abstract: Optical absorption spectroscopy was used to characterize the acid-induced conformational transition of horse heart ferrocytochrome c in the presence of urea. By using linear extrapolation to zero denaturant concentration, an apparent pK value for denaturation was found to be 0.86 +/- 0.07 at 25 degrees C. Visible absorption spectra in the presence of high urea concentration indicate that the dominant population is a high-spin, five-coordinate form under acidic conditions. Ferricytochrome c, used as a model reference system, shows a linear dependence of pK values versus urea concentration in the range from 0 to 4.1 M. Our data also indicate that even at a pH below 2 the iron-sulfur bond in ferrocytochrome c is present.
authors.affiliation: Department of Biophysics, Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 043 53 Kosice, Slovakia.
authors.forename: Rastislav
authors.initials: R
authors.lastname: Varhac
authors.forename: Marián
authors.initials: M
authors.lastname: Antalík
mesh_terms: D000818:Animals; D003574:Cytochrome c Group / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry; D006736:Horses; D006851:Hydrochloric Acid / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009206:Myocardium / Q000201:enzymology; D010084:Oxidation-Reduction; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D013056:Spectrophotometry, Ultraviolet; D014508:Urea
chemical_list: D003574:Cytochrome c Group; D005290:Ferric Compounds; D005296:Ferrous Compounds; C083951:cytochrome c553; D014508:Urea; D006851:Hydrochloric Acid