Water induced TSDC in hemoglobin and myoglobin

The hydration of hemoglobin (Hb) and myoglobin (Mb) has been investigated by the Thermally Stimulated Depolarization Currents (TSDC) technique. The TSDC spectra as a function of the hydration degree (δ=0.01+0.3 grams of water/grams of protein) and of the annealing time in vacuum were recorded in the temperature range 100-300 K on pellet samples. The distribution of water dipoles for both heme-proteins shows four main peaks in the range 170-300 K, indicating the presence of at least four different classes of bound water. A fifth peak at very low temperatures (T_m~150 K) appears only at low hydration levels and probably it is not related to water dipole relaxations. Possible environments of water dipoles responsible for the TSDC peaks are discussed