Homogeneous enzymatic reactions in ionic liquids with poly(ethylene glycol)-modified subtilisin

Subtilisin Carlsberg was covalently modified with comb-shaped poly(ethylene glycol) (PM13). PM13-modified subtilisin (PM13-Sub) was readily solubilized in three different ionic liquids (ILs), i.e., Emim]Tf2N], C2OC1mim]Tf2N] and C2OHmim]Tf2N]. Analysis of homogeneous enzymatic reactions in the ILs revealed that PM13-Sub exhibited excellent catalytic performance while the native enzyme suspended in ILs showed no activity. Hydrophobicity of ILs slightly affected enzyme activity, and the relatively hydrophobic IL Emim]Tf2N] was the preferred medium for enzymatic reactions, similar to enzymatic reactions in conventional organic solvents. Enzyme activity was much higher in Emim]Tf2N] than in conventional organic solvents, and excellent activity was associated with unique properties of ILs such as hydrophobicity and high polarity. Furthermore, PM13-Sub showed good stability in Emim]Tf2N], and maintained 80% of its initial activity after 60 h.