Contributions of polar and apolar groups to the thermodynamic stability of azurin

All denaturational thermodynamic changes (ΔH, ΔS, ΔG) were calculated for the thermal unfolding of azurin from Pseudomonas Aeruginosa. DSC data could not be directly studied in terms of classical thermodynamics, because the thermal unfolding of azurin is an irreversible process. However, a mathematical extrapolation of heat capacity curves to infinite scan rate allowed us to obtain the denaturational enthalpy change and the melting temperature related to the reversible step. The denaturational heat capacity change (ΔCp), together with all the relevant contributions of polar and apolar groups to the thermodynamic parameters of azurin were calculated according to an approach taking into account the common features of protein unfolding and dissolution of model compounds. A comparison between the experimental and the expected denaturational thermodynamic values was briefly discussed. © 1996 Società Italiana di Fisica.