Relevance of Frank’s solvent classification as typically aqueous and typically non-aqueous to activities of firefly luciferase, alcohol dehydrogenase, and α-chymotrypsin in aqueous binaries

Effects of cosolvent concentration on activity of fire fly luciferase, α-chymotrypsin, and alcohol dehydrogenase from baker’s yeast (Saccharomyces cerevisiae) have been studied for several solvents with varying hydrophobicities (log P from +1.0 to −1.65) and polarities (dielectric constant from 7.4 to 109). The inhibitory effect of the cosolvent is examined in light of Frank’s classification of solvents into ‘typically aqueous (TA)’ and ‘typically non-aqueous (TNA).’ The solvent concentration at which the enzyme activity decreases to half, the C50 values, for TA solvents such as 1-cyclohexyl-2-pyrrolidinone, 2-butoxyethanol, 1-methyl-2-pyrrolidinone, tetrahydrofuran, t-butanol, and ethanol correlate quite well with their critical hydrophobic interaction concentration, rather than log P, while those for TNA solvents such as acetonitrile, dimethyl formamide, formamide, and dimethyl sulfoxide correlate well with log P. The interactions of TA solvents with proteins appear to be governed mainly by hydrophobic interactions while both hydrophobic and hydrophilic interactions play important role in case of TNA solvents.