Thermostable α-amylase immobilization: Enhanced stability and performance for starch biocatalysis

Covalent immobilization of α-amylase on hollow metal organic framework coated magnetic phase-change microcapsules for the improvement of its thermostability

Exploring efficient immobilized carrier for α-Amylase (α-Amy) to enhance its thermostability has significant influence in starch related industry. Here, hollow ZIF-8 (HZIF-8) with amino groups coated magnetic phase change microcapsules (PCM) was designed for covalent immobilization of α-Amy. Magnetic PCM consisting n-docosane core and SiO2/Fe3O4 hybrid shell were firstly synthesized. Then, HZIF-8 shell with amino groups was coated and α-Amy was subsequently immobilized through covalent cross-linking strategy. The morphology, chemical structure and magnetic property of PCM@HZIF-8@α-Amy (PCMHA) were comprehensively characterized. Moreover, heat control property of PCMHA was studied with encapsulation efficiency and thermal energy-storage efficiency of 50.55 % and 50.59 %, respectively. Catalytic activity of immobilized α-Amy was fully investigated with Km and Vmax of 2.773 mg/mL and 1.853 μmol/mL·min, respectively. From reusability and storage stability study, immobilized α-Amy not only maintained rather high activity after 9 cycles' reuse, but also exhibited good activity under high salt ion condition after 7 days.

Amylases from thermophilic bacteria: structure and function relationship

Amylases hydrolyze starch to diverse products including dextrins and progressively smaller polymers of glucose units. Thermally stable amylases account for nearly 25% of the enzyme market. This review highlights the structural attributes of the α-amylases from thermophilic bacteria. Heterologous expression of amylases in suitable hosts is discussed in detail. Further, specific value maximization approaches, such as protein engineering and immobilization of the amylases are discussed in order to improve its suitability for varied applications on a commercial scale. The review also takes into account of the immobilization of the amylases on nanomaterials to increase the stability and reusability of the enzymes. The function-based metagenomics would provide opportunities for searching amylases with novel characteristics. The review is expected to explore novel amylases for future potential applications.

Immobilization of α-amylase on GO-magnetite nanoparticles for the production of high maltose containing syrup

Robust amylases with stability and catalysis at multitude of extremities are the need of an hour. Enzyme immobilization may prove beneficial at commercial scale to achieve such attributes. In the present study, a commercially available amylase was immobilized on graphene oxide (GO) - magnetite (Fe₃O₄) nanoparticles through covalent bonding. The structural and morphological characterizations were conducted by XRD, SEM and TEM. Further, FTIR and TGA confirmed the interaction between amylase, GO and nanoparticles. The variables, such as concentrations of GO (1.3 mg), Fe₃O₄ (58 μg), and amylase (4.5 mg) were optimized by the response surface methodology using central composite design. High loading capacity of 77.58 μg amylase over 1 μg GO-magnetite nanoparticles was achieved under optimum conditions. Biochemically, the pH optimum remained unaltered, i.e., pH 7, whereas, the alkalitolerance was increased by ~20% in relative activities upon immobilization. The half-life of soluble amylase was 13 h, which enhanced to 20 h upon immobilization in 20 mM phosphate buffer, pH 7 at 50 °C. Besides, the thermodynamic parameters supported the stability trends. The immobilized amylase could be used for 11 subsequent cycles. The mentioned attributes and the dextrose equivalent values during the production of high maltose containing syrup highlighted its commercialization.

Enantioconvergent hydrolysis of m-nitrostyrene oxide at an elevated concentration by Phaseolus vulgaris epoxide hydrolase in the organic/aqueous two-phase system

(R)-m-Nitrophenyl-1,2-ethanediol (m-NPED) is a versatile and highly value-added chiral building block for the synthesis of some bioactive compounds, such as (R)-Nifenalol. To efficiently produce (R)-m-NPED through the enantioconvergent hydrolysis of racemic (rac-) m-nitrostyrene oxide (m-NSO) using the whole resting cells of Escherichia coli/pCold-pveh2 intracellularly expressing PvEH2, an epoxide hydrolase from Phaseolus vulgaris, two reaction systems were investigated. In the Na₂ HPO₄ -NaH₂ PO₄ buffer (50 mmol l^-1 , pH 7·0) system, merely 15 mmol l^-1 rac-m-NSO was successfully subjected to enantioconvergent hydrolysis, producing (R)-m-NPED with 86·0% enantiomeric excess (ee_p ) and 177·6 mg l^-1  h^-1 space-time yield (STY). The experimental result indicated that there is inhibitory effect of rac-m-NSO at high concentration on PvEH2. To efficiently increase the concentration of rac-m-NSO and the STY of (R)-m-NPED, petroleum ether was first selected to construct an organic/aqueous two-phase system. Then, both the volume ratio (v_o /v_b ) of petroleum ether to phosphate buffer and the weight ratio (w_c /w_s ) of E. coli/pCold-pveh2 dry cells to rac-m-NSO were optimized as 2 : 8 and 5 : 1, respectively. In the optimized petroleum ether/phosphate buffer two-phase system, the enantioconvergent hydrolysis of rac-m-NSO at 40 mmol l^-1 (6·6 mg ml^-1 ) was carried out at 25°C for 12 h using 33·0 mg ml^-1 vacuum freeze-dried cells of E. coli/pCold-pveh2, producing (R)-m-NPED with 87·4% ee_p , 82·3% yield and 502·4 mg l^-1  h^-1 STY. SIGNIFICANCE AND IMPACT OF THE STUDY: Epoxide hydrolases play a crucial role in producing enantiopure epoxides and/or vicinal diols. However, numerous biocatalytic reactions of organic compounds, such as epoxides, in aqueous phase suffered various restrictions. Herein, the enantioconvergent hydrolysis of rac-m-NSO in two reaction systems was investigated using the whole cells of Escherichia coli/pCold-pveh2. As a result, the concentration of rac-m-NSO and the space-time yield of (R)-m-NPED in organic/aqueous two-phase system were significantly increased, when compared with those in aqueous phase. To our knowledge, this is the first report about the production of (R)-m-NPED from rac-m-NSO at an elevated concentration by PvEH2 in the two-phase system.