Thermodynamic domain analysis of fresh and incubated human apotransferrin

The thermal denaturation of human apotransferrin was studied by a differential scanning calorimeter (DSC) in 100 mM Hepes buffer at pH 7.0. Deconvolution analysis of excess molar heat capacity was adjusted by four transitions of which two transitions were linked to N-domain and the remaining two were connected to C-domain. The same experiment was carried out for the incubated sample for a period of 24 h at 27 °C. The deconvolution subpeaks exhibited five transitions. The free energy, ΔGH2O∘, in the absence of sodium n-dodecyl sulphate (SDS), as a criterion of stability measurement, was obtained based on Pace theory on UV spectrophotometry. The result indicates that incubated sample was stabilized by 14 kJ mol−1 relative to the fresh sample. The circular dichroism (CD) study confirms the presence of additional secondary structures for the incubated sample compared with the fresh one because of Hepes molecule interaction with protein domains.