Catalytic activity of α-chymotrypsin in enzymatic peptide synthesis in ionic liquids

The catalytic activity of α-chymotrypsin in the enzymatic peptide synthesis of N-acetyl-l-tryptophan ethyl ester with glycyl glycinamide was examined in ionic liquids and organic solvents. The water content in 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([emim][FSI]) affected the initial rates of peptide synthesis and hydrolysis. The activity of α-chymotrypsin was influenced by a kind of anions consisting of the same cation, [emim], when an ionic liquid was used as a solvent. The initial rate of peptide synthesis was improved 16-fold by changing from an organic solvent, acetonitrile, to an ionic liquid, [emim][FSI], at 25 °C. The activity of α-chymotrypsin in the peptide synthesis in [emim][FSI] was 17 times greater than that in acetonitrile at 60 °C, although the activity of α-chymotrypsin in the peptide synthesis gradually decreased with an increase in reaction temperature in [emim][FSI], similar to organic solvents. Moreover, α-chymotrypsin exhibited activity in [emim][FSI] and [emim][PF6] at 80 °C.