PHYSICAL
AND BIOPHYSICAL CHEMISTRY DIVISION
COMMISSION
ON BIOPHYSICAL CHEMISTRY
Measurement and analysis of results obtained on biological substances
with differential scanning calorimetry (IUPAC Technical Report)
Hans-Jürgen Hinz1 and Frederick P. Schwarz2
1Institut für Physikalische Chemie, Westfalische
Wilhelms-Universität, Schlossplatz 4/7 D-48149, Münster, Germany;
2Center for Advanced Research in Biotechnology/National Institute of
Standards and Technology, 9600 Gudelsky Drive, Rockville, Maryland 20850,
USA
Abstract: Differential scanning calorimeters (DSCs)
have been widely used to determine the thermodynamics of phase transitions
and conformational changes in biological systems including proteins,
nucleic acid sequences, and lipid assemblies. DSCs monitor the temperature
difference between two vessels, one containing the biological solution
and the other containing a reference solution, as a function of temperature
at a given scan rate. Recommendations for DSC measurement procedures,
calibration procedures, and procedures for testing the performance of
the DSC are described. Analysis of the measurements should include a
correction for the time response of the instrument and conversion of
the power vs. time curve to a heat capacity vs. temperature plot. Thermodynamic
transition models should only be applied to the analysis of the heat
capacity curves if the model-derived transition temperatures and enthalpies
are independent of the DSC scan rate. Otherwise, kinetic models should
be applied to the analysis of the data. Application of thermodynamic
transition models involving two states, two states and dissociation,
and three states to the heat capacity vs. temperature data are described.
To check the operating performance with standard DSCs, samples of 1
to 10 mg mL1 solutions of hen egg white lysozyme in
0.1 M HCl-glycine buffer at pH = 2.4 ± 0.1 were sent to six different
DSC laboratories worldwide. The values obtained from proper measurements
and application of a two-state transition model yielded an average unfolding
transition temperature for lysozyme of 331.2 K with values ranging from
329.4 to 331.9 K, and an average transition enthalpy of 405 kJ mol1
with values ranging from 377 to 439 kJ mol1. It is
recommended that the reporting of DSC results be specific with regard
to the composition of the solution, the operating conditions and calibrations
of the DSC, determination of base lines that may be model-dependent,
and the model used in the analysis of the data.
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