A mechanistic study on the thermal unfolding of cytochrome c in presence of 4-chlorobutan-1-ol: Differential scanning calorimetric and spectroscopic approach

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A mechanistic study on the thermal unfolding of cytochrome c in presence of 4-chlorobutan-1-ol: Differential scanning calorimetric and spectroscopic approach

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Title: A mechanistic study on the thermal unfolding of cytochrome c in presence of 4-chlorobutan-1-ol: Differential scanning calorimetric and spectroscopic approach
Author: MEHTA, R; KUNDU, A; KISHORE, N
Abstract: Extensive studies have been carried out on thermal unfolding and conformational characterization of cytochrome c in the presence of 4-chlorobutan-1-ol at pH 4.0, 6.0 and 7.0 using micro differential scanning calorimetry, fluorescence, and circular dichroism measurements. Cytochrome c follows a simple two-state reversible thermal unfolding in the presence of low concentration (<25 x 10(-3) mol dm(-3)) of the alcohol at pH 4.0 as reflected by equal calorimetric and van't Hoff enthalpies. However, at concentrations higher than 50 x 10(-3) mol dm(-3), the calorimetric transitions are irreversible and scan rate dependent, thus restricting the application of equilibrium thermodynamics. It has been observed that between 25 x 10(-3) mol dm(-3) and 50 x 10(-3) mol dm(-3) alcohol concentration, cytochrome c exists in two conformational states at pH 4.0 following N &REVARR; E &RARR; U unfolding mechanism, where N &REVARR; E transition occurs at 67.6&DEG;C and E &RARR; U at 83.0&DEG;C. The spectroscopic results indicate that the protein at 83.0&DEG;C (where the second transition ends) in the presence of the alcohol is in the molten globule state. Quantitative thermodynamic parameters accompanying the thermal denaturation process have been evaluated. 4-Chlorobutan-1-ol has also been observed to induce cooperative thermal transitions in cytochrome c at pH 6.0 and 7.0 whereas in the absence of the alcohol, no thermal transition is observed. From the scan rate dependent irreversible thermal transitions, an average activation energy of 136 &PLUSMN; 2 U mol(-1) has been calculated.
URI: http://dx.doi.org/10.1039/b311845b
http://dspace.library.iitb.ac.in/xmlui/handle/10054/11664
http://hdl.handle.net/10054/11664
Date: 2003


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