AbstractIn this paper, we compare the activities of subtilisin and thiolsubtilisin in anhydrous organic solvents and in mixtures of water and miscible organic media. The information obtained indicates that changing from one organic solvent to another does not significantly affect the stability of the transition state for the reaction. Thus, since the transition state is charged, it is likely that the active site of the enzyme is electrostatically protected from bulk solvent. Further, since the activities of subtilisin and thiolsubtilisin are different in the solvents used, it is clear that the active site serine is a catalytically important residue in both water and organic solvents.
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