Direct observation of the enthalpy change accompanying the native to molten-globule transition of cytochrome c by using isothermal acid-titration calorimetry.
The enthalpy change accompanying the reversible acid-induced transition from the native (N) to the molten-globule (MG) state of bovine cytochrome c was directly evaluated by isothermal acid-titration calorimetry (IATC), a new method for evaluating the pH dependence of protein enthalpy. The enthalpy change was 30 kJ/mol at 30 degrees C, pH 3.54, with 500 mM KCl. The results of the global analysis of the temperature dependence of the excess enthalpy from 20 to 35 degrees C demonstrated that the N to MG transition is a two-state transition with a small heat capacity change of 1.1 kJ K(-1) mol(-1). The present findings were also indicative of the pH dependence of the enthalpy and the heat capacity of the MG state, -13 kJ mol(-1) pH(-1) and -1.0 kJ K(-1) mol(-1) pH(-1), respectively, at 30 degrees C within a pH range from 2 to 3.
Nakamura
Shigeyoshi
S
Department of Bioengineering, Nagaoka University of Technology, 1603-1 Kamitomioka, Nagaoka 940-2188, Japan.
Kidokoro
Shun-ichi
S
D000818:Animals; D002151:Calorimetry; D002417:Cattle; D045304:Cytochromes c / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D011487:Protein Conformation; D017510:Protein Folding; D013816:Thermodynamics; D017186:Titrimetry
D045304:Cytochromes c