US Department of Energy Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA.
Biotechnol Bioeng. 2012 Feb;109(2):434-43. doi: 10.1002/bit.23352. Epub 2011 Oct 20.
We discuss the hydrolysis of cellulose using a pure cellulase: endo-1,4-β-D-glucanase (EG) from the fungus, Aspergillus niger, in buffer, the pure ionic liquid (IL), tris-(2-hydroxyethyl)-methylammonium methylsulfate (HEMA), and various mixtures of the two at different temperatures. Steady-state fluorescence and absorbance studies were performed to monitor the stability and activity of EG using cellulose azure as the substrate. EG attains its highest activity at 45°C in buffer and denatures at ∼55°C. On the other hand, HEMA imparts substantial stability to the enzyme, permitting the activity to peak at 75°C. The relative roles of temperature, viscosity, pH, polarity, and the constituent ions of the ILs on the hydrolysis reaction are examined. It is demonstrated that pretreatment of cellulose with ILs such as BMIM Cl, MIM Cl, and HEMA results in more rapid conversion to glucose than hydrolysis with cellulose that is not pretreated. The percent conversion to glucose from pretreated cellulose is increased when the temperature is increased from 45 to 60°C. Two different ILs are used to increase the efficiency of cellulose conversion to glucose. Cellulose is pretreated with BMIM Cl. Subsequent hydrolysis of the pretreated cellulose in 10-20% solutions of HEMA in buffer provides higher yields of glucose at 60°C. Finally, to our knowledge, this is the first study dealing with a pure endoglucanase from commercial A. niger. This enzyme not only shows higher tolerance to ILs, such as HEMA, but also has enhanced thermostability in the presence of the IL.
我们讨论了纤维素的水解，使用的是一种纯纤维素酶：内切-1,4-β-D-葡聚糖酶（EG），来自真菌黑曲霉，在缓冲液、纯离子液体（IL）三（2-羟乙基）甲基氯化铵甲基硫酸盐（HEMA）以及这两种物质的不同混合物中，在不同温度下进行反应。使用纤维素蓝作为底物，通过稳态荧光和吸光度研究来监测 EG 的稳定性和活性。EG 在缓冲液中的最适活性温度为 45°C，在约 55°C时变性。另一方面，HEMA 赋予酶很大的稳定性，使活性在 75°C时达到峰值。考察了温度、粘度、pH 值、极性以及 IL 组成离子对水解反应的相对作用。结果表明，用 IL 如 BMIM Cl、MIM Cl 和 HEMA 预处理纤维素会导致比未经预处理的纤维素更快地转化为葡萄糖。当温度从 45°C升高到 60°C时，预处理纤维素的葡萄糖转化率会增加。使用两种不同的 IL 来提高纤维素转化为葡萄糖的效率。用 BMIM Cl 预处理纤维素。随后在缓冲液中 10-20%的 HEMA 溶液中对预处理的纤维素进行水解，在 60°C 下可获得更高的葡萄糖产率。最后，据我们所知，这是首次研究来自商业黑曲霉的纯内切葡聚糖酶。这种酶不仅对 HEMA 等 IL 具有更高的耐受性，而且在 IL 存在下还具有增强的热稳定性。
