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Interaction mechanism of an antidiabetic agent, 1-deoxynojirimycin (DNJ) with its target protein α-glucosidase (maltase), was investigated by kinetics, fluorescence spectroscopy, UV-vis spectroscopy, circular dichroism, dynamic light scattering coupled with molecular docking analysis. It was found that DNJ reversibly inhibited activity of maltase through a mixed-type manner with IC of (1.5±0.1) μM and inhibition constant K of (2.01±0.02) μM. Fluorescence data and UV-vis information confirmed that the intrinsic fluorescence of maltase was quenched by DNJ through a dynamic quenching procedure due to the collision of them. The calculated thermodynamic parameters including enthalpy change, entropy change and Gibbs free energy change indicated that their binding was spontaneous and the driven force was hydrophobic interaction. Besides, circular dichroism analysis displayed that their binding resulted conformational changes of maltase, characterizing by a decrease of α-helix and an increase in β-sheet. Dynamic light scattering measurements demonstrated the reduction in the hydrodynamic radii of maltase. Further molecular docking revealed that DNJ formed hydrogen bonds with catalytic residues Asp68, Arg212, Asp214, Glu276, Asp349 and Arg439 of maltase, then inhibited the enzyme activity by occupying catalytic center. This study provided a comprehensively understanding about the action mechanism of DNJ on maltase.

The goal of this study was to develop a cheap and simple medium and to optimize fermentation parameters for fibrinolytic enzyme production by Bacillus subtilis WR350. A low-cost medium containing 35 g/L sucrose, 20 g/L corn steep powder and 2 g/L MgSO 4 ·7H 2 O was developed via single-factor and orthogonal experiments. A cheap nitrogen source, corn steep powder, was used to replace the soy peptone present in the initial medium. The highest fibrinolytic activity of 5865 U/mL was achieved using the optimized medium in a 100-L fermenter with an aeration rate of 1.0 vvm and an agitation speed of 200 rpm. The resulting enzyme yield was among the highest described in the literature with respect to fibrinolytic activity, as determined by the fibrin plate method. Techno-economic evaluation indicated that the cost of the optimized medium was only 8.5% of the cost of the initial medium, and the total fermentation cost of fibrinolytic enzyme production using the optimized medium was 23.35% of the cost of using the initial medium.

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