College of Chemistry and Chemical Engineering, Lingnan Normal University, Cunjin Road 29, Chikan District, Zhanjiang, 524048, Guangdong, China.
Amino Acids. 2020 May;52(5):771-780. doi: 10.1007/s00726-020-02850-3. Epub 2020 May 5.
Gamma-aminobutyric acid (GABA) biosynthesis depended to a great extent on the biotransformation characterization of glutamate decarboxylase (GAD) and process conditions. In this paper, the enhancing effect of D101 macroporous adsorption resin (MAR) on the GABA production was investigated based on the whole-cell biotransformation characterization of Enterococcus faecium and adsorption characteristics of D101 MAR. The results indicated that the optimal pH for reaction activity of whole-cell GAD and pure GAD was 4.4 and 5.0, respectively, and the pH range retained at least 50% of GAD activity was from 4.8 to 5.6 and 4.0-4.8, respectively. No substrate inhibition effect was observed on both pure GAD and whole-cell GAD, and the maximum activity could be obtained when the initial L-glutamic acid (L-Glu) concentration exceeded 57.6 mmol/L and 96.0 mmol/L, respectively. Besides, GABA could significantly inhibit the activity of whole-cell GAD rather than pure GAD. When the initial GABA concentration of the reaction solution remained 100 mmol/L, 33.51 ± 9.11% of the whole-cell GAD activity was inhibited. D101 MAR exhibited excellent properties in stabilizing the pH of the conversion reaction system, supplementing free L-Glu and removing excess GABA. Comparison of the biotransformation only in acetate buffer, the GABA production, with 50 g/100 mL of D101 MAR, was significantly increased by 138.71 ± 5.73%. D101 MAR with pre-adsorbed L-Glu could significantly enhance the production of GABA by gradual replenishment of free L-Glu, removing GABA and maintaining the pH of the reaction system, which would eventually make the GABA production more economical and eco-friendly.
γ-氨基丁酸（GABA）的生物合成在很大程度上取决于谷氨酸脱羧酶（GAD）的生物转化特性和工艺条件。本文基于屎肠球菌全细胞生物转化特性和 D101 大孔吸附树脂的吸附特性，研究了 D101 大孔吸附树脂对 GABA 生产的增强作用。结果表明，全细胞 GAD 和纯 GAD 的反应活性最佳 pH 值分别为 4.4 和 5.0，pH 值范围保留至少 50%GAD 活性分别为 4.8-5.6 和 4.0-4.8。纯 GAD 和全细胞 GAD 均无底物抑制效应，当初始 L-谷氨酸（L-Glu）浓度分别超过 57.6 mmol/L 和 96.0 mmol/L 时，可获得最大活性。此外，GABA 能显著抑制全细胞 GAD 的活性，而不是纯 GAD。当反应液中 GABA 的初始浓度保持在 100 mmol/L 时，全细胞 GAD 活性的 33.51%±9.11%被抑制。D101 大孔吸附树脂在稳定转化反应系统的 pH 值、补充游离 L-Glu 和去除多余 GABA 方面表现出优异的性能。与仅在乙酸盐缓冲液中进行生物转化相比，添加 50 g/100 mL 的 D101 大孔吸附树脂，GABA 的产量显著提高了 138.71%±5.73%。预先吸附 L-Glu 的 D101 大孔吸附树脂可通过逐步补充游离 L-Glu、去除 GABA 和维持反应系统的 pH 值，显著提高 GABA 的产量，从而使 GABA 的生产更经济、更环保。
