On the salt-induced activation of lyophilized enzymes in organic solvents:Effect of salt kosmotropicity on enzyme activity

The dramatic activation of enzymes in nonaqueous media upon co-lyophilizati on with simple inorganic salts has been investigated as a function of the J ones-Dole B coefficient, a thermodynamic parameter for characterizing the s alt's affinity for water and its chaotropic (water-structure breaking) or k osmotropic (water-structure making) character. In general, the water conten t, active-site content, and transesterification activity of freeze-dried su btilisin Carlsberg preparations containing >96% w/w salt increased with inc reasing kosmotropicity of the activating salt. Degrees of activation relati ve to the salt-foe enzyme ranged from 33-fold for chaotropic sodium iodide to 2480-fold for kosmotropic sodium acetate. Exceptions to the general tren d can be explained by the mechanical properties and freezing characteristic s of the salts undergoing lyophilization. The profound activating effect ca n thus be attributed in part to the stabilizing (salting-out) effect of kos motropic salts and the phenomenon of preferential hydration.