A new method for determining the constant-pressure heat capacity change associated with the protein denaturation induced by guanidinium chloride (or urea)

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• 作者：Ritu Singh ; Tanveer Ali Dar ; Sh ; ar Ahmad ; Ali Akbar Moosavi-Movahedi ; Faizan Ahmad
• 关键词：Protein folding ; Protein denaturation ; Heat capacity
• 刊名：Biophysical Chemistry
• 出版年：2008
• 出版时间：March 2008
• 年：2008
• 卷：133
• 期：1-3
• 页码：81-89
• 全文大小：605 K

文摘

Differential scanning calorimetry (DSC) provides authentic and accurate value of ΔC_p^X, the constant-pressure heat capacity change associated with the N (native state)↔X (heat denatured state), the heat-induced denaturation equilibrium of the protein in the absence of a chemical denaturant. If X retains native-like buried hydrophobic interaction, ΔC_p^X must be less than ΔC_p^D, the constant-pressure heat capacity change associated with the transition, N↔D, where the state D is not only more unfolded than X but it also has its all groups exposed to water. One problem is that for most proteins D is observed only in the presence of chemical denaturants such as guanidinium chloride (GdmCl) and urea. Another problem is that DSC cannot yield authentic ΔC_p^D, for its measurement invokes the existence of putative specific binding sites for the chemical denaturants on N and D. We have developed a non-calorimetric method for the measurements of ΔC_p^D, which uses thermodynamic data obtained from the isothermal GdmCl (or urea)-induced denaturation and heat-induced denaturation in the presence of the chemical denaturant concentration at which significant concentrations of both N and D exist. We show that for each of the proteins (ribonuclease-A, lysozyme, α-lactalbumin and chymotrypsinogen) ΔC_p^D is significantly higher than ΔC_p^X. ΔC_p^D of the protein is also compared with that estimated using the known heat capacities of amino acid residues and their fractional area exposed on denaturation.