离子液体的组成及溶剂性质与木瓜蛋白酶催化特性的关系

离子液体的组成及溶剂性质对木瓜蛋白酶催化D,L-对羟基苯甘氨酸甲酯不对称水解反应有重要的影响. 木瓜蛋白酶在含CnMIm·BF4(n=2~6)介质中表现出较高的活性、对映体选择性及稳定性, 而在含有C4MIm·HSO4, C4MIm·Cl, C4MIm·NO3, C4MIm·CH3COO的介质中表现较低的对应值. 在含有CnMIm·BF4(n=2~6)的介质中, 酶活性随离子液体的极性增大而提高, 但在含有C4MIm·HSO4, C4MIm·Cl, C4MIm·NO3, C4MIm·CH3COO的介质中随离子液体的极性增大反而降低. 木瓜蛋白酶的对映体选择性和稳定性均随着离子液体的疏水性增大而提高. 荧光分析结果表明, 离子液体对酶分子构象具有显著的影响. 在CnMIm·BF4(n=2~6)的介质中, 木瓜蛋白酶的最大荧光发射波长(λmax)均蓝移, 而在含有C4MIm·HSO4, C4MIm·Cl, C4MIm·NO3或C4MIm·CH3COO的介质中, λmax均红移. 与CnMIm·BF4(n=2~6)相比, 在C4MIm·HSO4, C4MIm·Cl, C4MIm·NO3或C4MIm·CH3COO中, 酶分子构象的变化较大, 暴露的疏水区域较多.

Correlation Between Catalytic Characteristics of Papain and Components and Solvent Properties of Ionic Liquids

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 CnMIm·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 CnMIm·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 CnMIm·BF4(n=2—6)-containing systems, a blue-shift of the maximal emission(λmax) of papain occurred, while a red-shift of λmax 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 CnMIm·BF4(n=2—6), resulting in more exposure of hydrophobic regions of the enzyme.