亲水性离子液体[EMIM]BF_4对固定化β-葡萄糖醛酸苷酶催化活性的影响

Effect of Hydrophilic Ionic Liquid [EMIM]BF_4 on the Catalytic Activity of Immobilized β-Glucuronidase

以壳聚糖为固定化载体,采用吸附交联法制备固定化β-葡萄糖醛酸苷酶;以1-乙基-3-甲基咪唑四氟硼酸盐([EMIM]BF4)/缓冲溶液均相体系为介质,研究了亲水性离子液体[EMIM]BF4对固定化酶生物催化甘草酸(GL)合成单葡萄糖醛酸基甘草次酸(GAMG)的影响.实验结果表明,当均相体系中[EMIM]BF4的体积分数为16%,pH为5.4,反应温度为50℃及摇床转速为200 r/min时,酶活力达到最高,并且明显优于纯缓冲溶液体系中的最高酶活.重复利用性实验结果表明,与纯缓冲液介质体系相比,固定化酶在含亲水性离子液体[EMIM]BF4的均相介质中表现出较好的操作稳定性.表观动力学参数和活化能数据表明,亲水性离子液体[EMIM]BF4在催化体系中能够增强酶和底物GL的亲和力,有效稳定酶-底物的过渡态,并降低反应活化能,而使固定化β-葡萄糖醛酸苷酶表现出较高的催化活性.

To improve hydrolysis of glycyrrhizin（GL） to glycyrrhetinic acid monoglucuronide（GAMG） possessing best biological function, Penicillium purpurogenum Li-3 strains highly expressing β-glucuronidase was screened by our workgroup in the initial research period. This enzyme was capable of promoting biotransformation process of GL to GAMG. With chitosan as carrier, immobilized β-glucuronidase was prepared by adsorption-crosslink technology in this work. With the purpose of studying the effect of hydrophilic ionic liquid BF4 on catalytic activity of immobilized β-glucuronidase, the [EMIM]BF4/buffer homogeneous system was used as bio-catalytic medium for immobilized β-glucuronidase to catalyze hydrolysis of GL to GAMG. The results showed that under the conditions of 16%（volume fraction）[EMIM]BF4, pH value of 5.4, the reaction temperature of 50℃ and the shaker rotate speed of 200 r/min, the enzyme activity could reach its maximum, and obviously higher than the highest enzyme activity in pure buffer medium system. After repeated recycling experiment, compared with that in pure buffer medium system, the immobilized β-glucuronidase showed excellent stability to repeated use in containing [EMIM]BF4 homogeneous medium system. The appa-rent kinetic parameters and activation energy data showed that the affinity between β-glucuronidase and its substance was enhanced by [EMIM]BF4 in biocatalytic medium, and the enzyme-substrate in the transition state was effectively stabilized, and the activation energy of the catalytic reaction was lowered, so that immobilized β-glucuronidase showed higher catalytic activity. This study provided the basis for design and application of new clean biological reactors and technology to improve the efficiency of enzymatic hydrolysis of GL to GAMG.