Differential scanning microcalorimetry study of the thermal denaturation of haemoglobin.

A study of thermal denaturation of human haemoglobin A0 (HbA0) and methaemoglobin (mHb) was carried out by differential scanning calorimetry. DSC haemoglobin profiles were scan rate dependent and only partly reversible. Thermal unfolding of protein was analysed with the use of both equilibrium thermodynamic and kinetic approaches. The fittings based on the simple equilibrium/dissociation model were good and much more satisfactory than those based on "fully-kinetic" models. However the presence of some kinetic distortion during the unfolding process should be noted due to the scan-rate effect on DSC transitions. The calculated first-order kinetic constant for mHb was higher by two orders than the one for HbA0 (stabilised form). The average activation energy for HbA0 was found to be 289 +/- 28 kJ M-1 while for mHb it was about 100 kj M-1 lower.