Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9573264 | Biophysical Chemistry | 2005 | 12 Pages |
Abstract
Thermal denaturation curves of lysozyme and ribonuclease-A were determined by measuring their far-UV circular dichroism (CD) spectra in the presence of different concentrations of five polyols (sorbitol, glycerol, mannitol, xylitol and adonitol) at various pH values in the range 7.0-1.9. The denaturation curve at each polyol concentration and pH was analysed to obtain values of Tm (midpoint of denaturation) and ÎHm (enthalpy change at Tm), and these ÎHm and Tm values obtained at different pH values were used to obtain ÎCp (constant-pressure heat capacity change) at each polyol concentration. Using values of ÎHm, Tm and ÎCp in the Gibbs-Helmholtz equation, ÎGD° (Gibbs energy change at 25 °C) was determined at a given pH and polyol concentration. Main conclusions of this study are that polyols have no significant effect on ÎGD° at pH 7.0, and they stabilise proteins in terms of ÎGD° against heat denaturation at lower pH values. Other conclusions of this study are: (i) Tm at each pH increases with increasing polyol concentration, (ii) ÎHm remains, within experimental error, unperturbed in the presence of polyols, and (iii) ÎCp depends on polyol concentration. Furthermore, measurements of the far- and near-UV CD spectra suggested that secondary and tertiary structures of both proteins in their native and denatured states are not perturbed on the addition of polyols.
Keywords
Related Topics
Physical Sciences and Engineering
Chemistry
Physical and Theoretical Chemistry
Authors
Inamul Haque, Rajendrakumar Singh, Ali Akbar Moosavi-Movahedi, Faizan Ahmad,