Abstract:

The components and solvent properties of ionic liquids(ILs) show an important impact on papain-catalyzed asymmetric hydrolysis of D,L-p-hydroxyphenylglycine methyl ester(D,L-HPGME). The enzyme was more active, enantioselective and stable in the C_nMIm·BF₄(n=2—6)-based systems, while it was less active, enantioselective and stable in the systems involving C₄MIm·HSO₄, C₄MIm·Cl, C₄MIm·NO₃ or C₄MIm·CH₃COO. Papain's activity increased with increasing the polarity of the ILs C_nMIm·BF₄(n=2—6) and, conversely, decreased with increasing the polarity of the ILs C₄MIm·HSO₄, C₄MIm·Cl, C₄MIm·NO₃ or C₄MIm·CH₃COO. Also, the more hydrophobic the IL was, the more enantioselective and stable the papain was. Fluorescence spectroscopic analysis demonstrates that ILs had an obvious effect on papain's conformation. In the C_nMIm·BF₄(n=2—6)-containing systems, a blue-shift of the maximal emission(λ_max) of papain occurred, while a red-shift of λ_max took place in the systems involving C₄MIm·HSO₄, C₄MIm·Cl, C4MIm·NO₃ or C₄MIm·CH₃COO. Papain's conformation changed greatly when the enzyme was placed in C₄MIm·HSO₄, C₄MIm·Cl, C₄MIm·NO₃ or C₄MIm·CH₃COO-based systems compared to those with C_nMIm·BF₄(n=2—6), resulting in more exposure of hydrophobic regions of the enzyme.

Key words: Papain, Ionic liquid; D,L-p-Hydroxyphenylglycine methyl ester, Catalytic characteristic, Fluorescence spectroscopic analysis