Effect of Enzyme Hydration on the Catalytic Activity of Chymotrypsin in Nearly Anhydrous Organic Suspensions

The relationship between enzyme hydration and the catalytic activity of chymo‐trypsin powders suspended in nearly anhydrous 1 M n‐propanol/toluene solutions has been studied. The enzyme hydration range examined extends from approximately 2 to 10 wt% water sorbed. Measurements of apparent enzyme activity and the number of active sites as a function of enzyme hydration were used to calculate intrinsic enzyme activity as a function of enzyme hydration. It was found that the apparent enzyme activity increased linearly over this hydration range and that approximately 30% of the enzyme was catalytically active independent of the hydration level. Thus, the observed increase in apparent catalytic activity with increasing enzyme hydration results from an increase in the catalytic efficiency of a fixed number of active sites, rather than an increase in the population of active sites. Inhibitor binding in the organic suspension was also measured using the transition state analogue, (R)‐1‐acetamido‐2‐phenylethane boronic acid, which binds reversibly to the active site of the enzyme. The inhibition results suggest that one role of water in activating nearly dry enzyme suspensions is to enhance the intrinsic catalytic activity through transition state stabilization.