Two types of hydration of bovine serum albumin, BSA, were found by Iilicrowave impedance dispersion according to Suzuki et al. (1. Phys Chem. 1996, 100, 7279). At 25.0 °C the number of the strongly bound water molecules, N., was 606 and that of the weakly bound water molecules, N_w, was 393 per one BSA molecule. Elevation of the temperature decreased Ns cohtinuously, whereas it-increased N_w discontinuously at 30 °C. Addition of an anesthetic halothane increased Nw at the expense of N.. At halothane 2.5 mM, Ns decreased by 300, and N_w increased by about 350. The electrical conductance of BSA solution showed a Iilinimum at about 1.0 mM halothane. The halothane concentration that showed the minimum electrical conductance coincided with the maximum in N_w. Because the volume fraction of BSA is less than 2.5%, the conductance change is attributable.to the change of bulk ion concentrations. The initial decrease of conductance represents the suppression of ionization by halothane. The increase of conductance above 1.0 InM halothane indicates unfolding of the protein, exposing polar moieties to water, thus increasing the ion concentration.
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