Salt-Induced Activation of Enzymes in Organic Solvents
Past studies of enzymatic catalysis in nearly anhydrous organic solvents have shown that the amount of water adsorbed to an enzyme in organic solvents is a critical determinant of enzyme activity, more important than the water content of the solvent itself (1,2). The exact amount of water associated with the enzyme, however, varies depending on the hydrophobicity of the solvent, with more hydrophilic solvents tending to strip adsorbed water from the enzyme surface (3). In the case of subtilisin Carlsberg, a particularly well-studied enzyme in organic media, a certain population of this essential water is intricately associated with the enzyme and does not exchange with water in the bulk organic solvent (4). Further water bound to the enzyme effects an increase in active-site polarity, which correlates closely with a sharp increase in enzyme activity (2). The correlation between increased activity and increased active-site polarity suggests various strategies for activating enzymes in organic media.
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