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

Abstract

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.