离子液体对木瓜蛋白酶催化特性的影响

研究了以1-丁基-3-甲基咪唑、四乙基铵及N-乙基吡啶为阳离子, 配以多种阴离子(H₂PO₄^-, ClO₄^-, HSO₄^-, CH₃COO^-, Cl^-, Br^-, NO₃^-, SCN^-, BF₄^-, PF₆^-)的离子液体对木瓜蛋白酶催化N-苯甲酰-L-精氨酸乙酯(BAEE)水解的活性及热稳定性的影响. 通过分析含离子液体体系中木瓜蛋白酶的水解活性和热力学失活参数, 发现该酶活性及稳定性与离子液体的Kosmotropicity性质无关. 因此, 离子的Hofmeister效应并不适合解释离子液体对木瓜蛋白酶催化特性的影响规律. 当以BF₄^-为阴离子, 改变阳离子结构时, 仅[BMIm][BF₄]可提高酶活性, 其它含官能团的咪唑类离子液体则降低酶活性, 但大部分离子液体明显提高木瓜蛋白酶的热稳定性. 在所研究的离子液体中, 基于PF₆^-或BF₄^-阴离子的离子液体可提高木瓜蛋白酶的活性及其热稳定性. 在含[BMIm][PF₆]介质中, 木瓜蛋白酶的水解活性最高; 在含[HOEtMIm][BF₄]介质中其热稳定性最好.

Influences of Ionic Liquids on Catalytic Performances of Papain

A series of ionic liquids(ILs) based on 1-butyl-3-methylimidazolium([BMIm]),N-ethylpyridi-nium(EPy)and tetraethylammonium([NET4]) cations with various kinds of anions(H2PO-4,ClO-4,HSO-4,CH3COO-,Cl-,Br-,NO-3,SCN-,BF-4,PF-6) was examined for their influences on papain-mediated hydrolysisof N-benzoyl-L-arginine ethyl ester.By assaying the hydrolysis activity and thermodynamics deactivationparameters of papain in all these IL-containing systems,it was found that there was no correlation between the enzymatic activity or thermostability and the ILs’ kosmotropicity.Thus,the Hofmeister effect was not regarded as a good explanation for remarkable effects of ILs on catalytic performance of papain.In the case of BF-4-based ILs combined with various cations,only [BMIm][BF4]enhanced the hydrolysis activity of papain,and other ILs lowered the enzymatic activity.However,most of all the tested ILs improved the enzymatic thermostability apart from the strong acidic one -[HOOCMMIm][BF4].Among all the examined ILs,the BF-4-or PF-6-based ILs markedly enhanced the activity or thermostability of papain.The enzyme exhibited the highest hydrolysis activity with [BMIm][PF6],and the best thermostability with [HOEtMIm][BF4].