Low-temperature Glass Transitions of Quenched and Annealed Bovine Serum Albumin Aqueous Solutions

¹ National Food Research Institute
² Department of Food Science and Technology, Tokyo University of Marine Science and Technology
³ Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology,

^* To whom correspondence should be addressed. E-mail: kiyoshik{at}nfri.affrc.go.jp.

Submitted on October 16, 2005
Revised on November 14, 2005
Accepted on 1 February 2006

	Abstract

To investigate the glass transition behaviors of a 20 % (w/w) aqueous solution of bovine serum albumin, heat capacities and enthalpy relaxation rates were measured by adiabatic calorimetry at temperatures ranging from 80 to 300 K. One series of measurements was carried out after quenching from 300 down to 80 K and another after annealing in 200-240 K. The quenched sample showed a heat capacity jump indicating a glass transition temperature T_g = 170 K, and the annealed sample showed a smaller jump with the T_g shifted towards the higher temperature side. The temperature dependence of the enthalpy relaxation rates for the quenched sample indicated the presence of two enthalpy relaxation effects: one at around 110 K and the other over a wide temperature range (120-190 K). The annealed sample showed three separate relaxation effects giving (1) T_g = 110 K, (2) 135 K, and (3) temperature higher than 180 K, while nothing around 170 K. These effects were thought to originate, respectively, from the rearrangement motions of (1) primary hydrate water forming a direct hydrogen-bond with the protein, (2) part of the internal water localized in the opening of a protein structure, and (3) the disordered region in the protein.

Key Words: Adiabatic Calorimetry, Bovine Serum Albumin, Enthalpy Relaxation, Glass Transition, Protein Hydration

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