Calorimetric Study of Helix aspersa Maxima Hemocyanin Isoforms

The thermal unfolding of hemocyanin isoforms, β -HaH and α D + N -HaH, isolated from the hemolymph of garden snails Helix aspersa maxima, was studied by means of differential scanning calorimetry (DSC). One transition, with an apparent transition temperature ( T m ) at 79.88°C, was detected in the thermogram of β -HaH in 20 mM HEPES buffer, containing 0.1 M NaCl, 5 mM CaCl 2, and 5 mM MgCl 2 , pH 7.0, at scan rate of 1.0°C min −1 . By means of successive annealing procedure, two individual transitions were identified in the thermogram of α D + N -HaH. Denaturation of both hemocyanins was found to be an irreversible process. The scan-rate dependence of the calorimetric profiles indicated that the thermal unfolding of investigated hemocyanins was kinetically controlled. The thermal denaturation of the isoforms β -HaH and α D + N -HaH was described by the two-state irreversible model, and parameters of the Arrhenius equation were calculated.