HEAT-CAPACITY AND THERMODYNAMIC CHARACTERISTICS OF DENATURATION AND GLASS-TRANSITION OF HYDRATED AND ANHYDROUS PROTEINS

Calorimetric measurements of absolute heat capacity have been performe d for hydrated S-11-globulin (0 < C-H2O < 25%) and for lysozyme in a c oncentrated solution, both in the native and denatured states. The den aturation process is observed in hydrated and completely anhydrous pro teins; it is accompanied by the appearance of heat capacity increment (Delta(N)(D)C(p)), as is the case for protein solutions. It has been s hown that, depending on the temperature and water content, the hydrate d denatured proteins can be in a highly elastic or glassy states. Glas s transition is also observed in hydrated native proteins. It is found that the denaturation increment Delta(N)(D)C(p) in native protein, li ke the increment Delta C-p in denatured protein in glass transition at low water contents, is due to additional degrees of freedom of therma l motion in the protein globule. In contrast to the conventional notio n, comparison of absolute C-p values for hydrated denatured proteins w ith the C-p values for denatured proteins in solution has indicated a dominant contribution of the globule thermal motion to the denaturatio n increment of protein heat capacity in solutions. The concentration d ependence of denaturing heat absorption (temperature at its maximum, T -D, and thermal effect, Delta Q(D)) and that of glass transition tempe rature, T-g, for S-11-globulin have been studied in a wide range of wa ter contents. General polymeric and specific protein features of these dependencies are discussed. (C) 1997 Elsevier Science B.V.