Organic solvents strip water off enzymes

Exchange of enzyme‐bound H₂O with T₂O in aqueous solution followed by freeze drying provided tritiated water bound to chymotrypsin, subtilisin Carlsberg, and horseradish peroxidase. The desorption of T₂O from these enzymes suspended in various organic solvents showed that all three enzymes lost enzyme‐bound water with peroxidase losing the most T₂O of the three in solvents of moderate to high polarity. Polar solvent resulted in the highest degree of T₂O desorption (e.g., methanol desorbed from 56%‐62% of the bound T₂O), while nonpolar solvents resulted in the lowest degree of desorption (e.g., hexane desorbed from 0.4%–2% of the bound T₂O). Desorption is nearly immediate with most of the desorbable T₂O being released from the enzymes within the first 5 min. Both solvent dielectric and a measure of the saturated molar solubility of water in a given solvent provide accurate correlations between the properties of the organic solvents and the extent of T₂O desorption. This investigation shows that water stripping from an enzyme into a nonaqueous medium does occur and can be significant in polar solvents.