Electrochemistry of Unfolded Cytochrome c in Neutral and Acidic Urea Solutions
| Autor: | Jan Augustynski, Marian Antalik, Indiani C, Mikuláš Bánó, Milan Fedurco, Giulietta Smulevich, Erik Sedlák, John H. Dawson, Glascock Mc |
|---|---|
| Rok vydání: | 2005 |
| Předmět: |
Protein Folding
Protein Conformation Inorganic chemistry Acid–base titration Protonation Biochemistry Redox Medicinal chemistry Catalysis chemistry.chemical_compound Colloid and Surface Chemistry Electrochemistry medicine Metalloprotein Animals Urea Horses chemistry.chemical_classification biology Viscosity Chemistry Cytochrome c Cytochromes c General Chemistry Hydrogen-Ion Concentration Solutions Kinetics biology.protein Ferric Water binding Oxidation-Reduction medicine.drug |
| Zdroj: | Journal of the American Chemical Society. 127:7638-7646 |
| ISSN: | 1520-5126 0002-7863 |
| DOI: | 10.1021/ja050321g |
| Popis: | The present investigation reports the first experimental measurements of the reorganization energy of unfolded metalloprotein in urea solution. Horse heart cytochrome c (cyt c) has been found to undergo reversible one-electron transfer reactions at pH 2 in the presence of 9 M urea. In contrast, the protein is electrochemically inactive at pH 2 under low-ionic strength conditions in the absence of urea. Urea is shown to induce ligation changes at the heme iron and lead to practically complete loss of the alpha-helical content of the protein. Despite being unfolded, the electron-transfer (ET) kinetics of cyt c on a 2-mercaptoethanol-modified Ag(111) electrode remain unusually fast and diffusion controlled. Acid titration of ferric cyt c in 9 M urea down to pH 2 is accompanied by protonation of one of the axial ligands, water binding to the heme iron (pK(a) = 5.2), and a sudden protein collapse (pH < 4). The formal redox potential of the urea-unfolded six-coordinate His18-Fe(III)-H(2)O/five-coordinate His18-Fe(II) couple at pH 2 is estimated to be -0.083 V vs NHE, about 130 mV more positive than seen for bis-His-ligated urea-denatured cyt c at pH 7. The unusually fast ET kinetics are assigned to low reorganization energy of acid/urea-unfolded cyt c at pH 2 (0.41 +/- 0.01 eV), which is actually lower than that of the native cyt c at pH 7 (0.6 +/- 0.02 eV), but closer to that of native bis-His-ligated cyt b(5) (0.44 +/- 0.02 eV). The roles of electronic coupling and heme-flattening on the rate of heterogeneous ET reactions are discussed. |
| Databáze: | OpenAIRE |
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