PVA/CNTs/ZnO固定化L-AI和β-GAL双酶级联高效绿色制备D-塔格糖的应用研究

    The application of PVA/CNTs/ZnO carrier-immobilized L-AI and β-GAL dual-enzyme cascade to the efficient green preparation of D-tagatose

    • 摘要: 为提高D-塔格糖的产量,从土壤样本中筛选并鉴定出可高效产L-阿拉伯糖异构酶(L-arabinose isomerase,L-AI)的微生物菌株,并通过araA基因克隆异源表达获得L-AI,随后通过制备聚乙烯醇/碳纳米管/氧化锌(PVA/CNTs/ZnO)固定化载体负载L-AI与β-半乳糖苷酶(β-Galactosidase,β-GAL)构建PVA/CNTs/ZnO@L-AI/β-GAL多酶反应体系,以提高D-塔格糖的合成效率。通过扫描电镜(SEM)、热重(TG)、红外光谱(FT-IR)和X射线光电子能谱(XPS),分析PVA/CNTs/ZnO固定化载体性能,并探讨PVA/CNTs/ZnO@L-AI/β-GAL的温度和pH等酶学性质。从土壤中筛选获得一株高产D-塔格糖的菌株,经鉴定为Bacillus amyloliquefaciens,命名为LW48,并在大肠杆菌中异源表达该菌株的araA基因得到L-AI。对PVA/CNTs/ZnO固定化载体的SEM、TG、FT-IR和XPS表征分析表明,PVA/CNTs/ZnO载体具有优良的稳定性。酶学性质分析表明,级联双酶L-AI和β-GAL的最佳温度和pH分别为65 ℃、pH 7.0,动力学参数vmax为0.187 mg·L-1·s-1,Km为6.02 mg·L-1;游离双酶L-AI和β-GAL的vmax为0.230 mg·L-1·s-1,Km为22.95 mg·L-1。此外,固定化级联双酶L-AI和β-GAL的最大转化率为42.9%,是游离双酶L-AI和β-GAL的3.25倍。通过制备PVA/CNTs/ZnO载体,提升了级联双酶L-AI和β-GAL生产D-塔格糖的水平,为D-塔格糖及稀有糖的工业化高效绿色生物制造提供了一种新的途径。

       

      Abstract: To improve the yield of D-tagatose, the initial step of this study was to screen and identify microorganisms capable of efficiently producing L-arabinose isomerase (L-AI) from soil samples. Subsequently, the araA gene was cloned and heterologously expressed to obtain L-AI. To enhance the synthesis efficiency of D-tagatose, L-AI and β-galactosidase (β-GAL) were co-immobilized on the prepared PVA/CNTs/ZnO carrier to construct a dual-enzyme reaction system. In addition, PVA/CNTs/ZnO immobilization carrier was analyzed by scanning electron microscopy (SEM), thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Furthermore, the optimal reaction temperature and pH of dual-enzyme cascade by the PVA/CNTs/ZnO@L-AI/β-GAL were investigated. In this study, a high-yield D-tagatose-producing strain named LW48, was identified as Bacillus amyloliquefaciens. The recombinant L-AI protein was obtained by cloning and expression. The dual-enzyme cascade of β-GAL and L-AI immobilized on the PVA/CNTs/ZnO carrier, along with the carrier itself, was characterized by SEM, TG, FT-IR, and XPS. The results showed that the PVA/CNTs/ZnO carrier had excellent stability. When lactose was used as the substrate, the optimal temperature and pH for L-AI were 65 ℃ and pH 7.0, respectively. The kinetic parameters for the vmax and Km of dual-enzyme cascade (β-GAL and L-AI) were 0.187 mg·L-1·s-1 and 6.02 mg·L-1, respectively. The vmax and Km of the free enzymes (β-GAL and L-AI) were 0.230 mg·L-1·s-1 and 22.95 mg·L-1, respectively. After 24 h of reaction under optimal conditions, the maximum conversion rate of the free enzymes was 13.2%. The maximum conversion rate of immobilized cascaded dual enzymes (L-AI and β-GAL) reached 42.9%, which was 3.25 times that of free enzymes(L-Al and β-GAL). In this study, the preparation of PVA/CNTs/ZnO carrier effectively improved the biosynthesis efficiency of β-GAL and L-AI dual-enzymes cascade for the green production of D-tagatose, providing a new approach for the industrialization of D-tagatose, with the efficient and green bio-manufacturing of rare sugars.

       

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