Anion-Specific Effects on the Alkaline State of Cytochrome c

AbstractSpecific effects of anions on the structure, thermal stability, and peroxidase activity of native (state III) and alkaline (state IV) cytochromec (cytc) have been studied by the UV-VIS absorbance spectroscopy, intrinsic tryptophan fluorescence, and circular dichroism. Thermal and isothermal denaturation monitored by the tryptophan fluorescence and circular dichroism, respectively, implied lower stability of cytc state IV in comparison with the state III. The pKa value of alkaline isomerization of cytc depended on the present salts, i.e., kosmotropic anions increased and chaotropic anions decreased pKa (Hofmeister effect on protein stability). The peroxidase activity of cytc in the state III, measured by oxidation of guaiacol, showed clear dependence on the salt position in the Hofmeister series, while cytc in the alkaline state lacked the peroxidase activity regardless of the type of anions present in the solution. The alkaline isomerization of cytc in the presence of 8 M urea, measured by Trp59 fluorescence, implied an existence of a high-affinity non-native ligand for the heme iron even in a partially denatured protein conformation. The conformation of the cytc alkaline state in 8 M urea was considerably modulated by the specific effect of anions. Based on the Trp59 fluorescence quenching upon titration to alkaline pH in 8 M urea and molecular dynamics simulation, we hypothesize that the Lys79 conformer is most likely the predominant alkaline conformer of cytc. The ...
Source: Biochemistry (Moscow) - Category: Biochemistry Source Type: research