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Thermodynamics of staphylococcal nuclease denaturation. I. The acid-denatured state

✍ Scribed by John H. Carra; Elizabeth A. Anderson; Peter L. Privalov

Publisher
Cold Spring Harbor Laboratory Press
Year
2008
Tongue
English
Weight
831 KB
Volume
3
Category
Article
ISSN
0961-8368

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✦ Synopsis

Abstract

Using high‐sensitivity differential scanning calorimetry, we reexamined the thermodynamics of denaturation of staphylococcal nuclease. The denaturational changes in enthalpy and heat capacity were found to be functions of both temperature and pH. The denatured state of staphylococcal nuclease at pH 8.0 and high temperature has a heat capacity consistent with a fully unfolded protein completely exposed to solvent. At lower pH values, however, the heat capacity of the denatured state is lower, resulting in a lower Δ__C~p~__ and Δ__H__ for the denaturation reaction. The acid‐denatured protein can thus be distinguished from a completely unfolded protein by a defined difference in enthalpy and heat capacity. Comparison of circular dichroism spectra suggests that the low heat capacity of the acid‐denatured protein does not result from residual helical secondary structure. The enthalpy and heat capacity changes of denaturation of a less stable mutant nuclease support the observed dependence of Δ__H__ on pH.

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