EFFECT OF WATER DIFFUSION LIMITATIONS ON THE THERMOSTABILITY OF ENZYMES IN NONAQUEOUS ENVIRONMENTS

The thermostability of anhydrous alpha-chymotrypsin has been analysed both in air and in organic solvents, with regard to the effect of the protein water-content on the course of deactivation. A higher initial water content increases the rate of inactivation. Deactivation tests c arried out under a constant thermodynamic activity of water indicate t hat reductions in dehydration rate lead to lower stability. The effect of water diffusion phenomena has also been studied. Protein aggregate s of larger size are less thermostable, thus indicating that diffusion al limitations to water transfer can play a significant role in thermo inactivation. The effect of water content on enzyme thermostability wa s also measured in the presence of two organic solvents of different h ydrophobicity. In both cases, the resulting increased thermolability c an be explained in terms of a limitation in water transfer towards the non-aqueous environment.