Expression, purification and characterization of catalase from Corynebacterium glutamicum / 生物工程学报

Catalase catalyzes the decomposition of H₂O₂ to H₂O and O₂, and has a wide range of industrial applications. However, most catalases used in the textile and paper industries are often subjected to high-alkaline challenges which makes it necessary to develop alkaline catalase. In this study, a catalase from Corynebacterium glutamicum was expressed in Escherichia coli, and the expression conditions were optimized. The recombinant catalase was purified by Ni-chelating affinity chromatography, and the recombinant enzyme was characterized. The optimal conditions of producing the recombinant catalase were: an IPTG concentration of 0.2 mmol/L, a culturing temperature of 25 °C and a culturing time of 11 h. The purified catalase had a specific activity of 55 266 U/mg, and it had a high activity in the pH range of 4.0 to11.5, with the highest activity at pH 11.0. When treated in pH 11.0 for 3 h, the enzyme retained 93% of its activity, indicating that the enzyme was qualified with a favorable stability under high-alkaline condition. The recombinant catalase had maximal activity at 30 °C, and showed a satisfactory thermal stability at a range of 25 °C to 50 °C. The apparent Km and Vmax values of purified catalase were 25.89 mmol/L and 185.18 mmol/(minmg), respectively. Besides, different inhibitors, such as sodium dodecyl sulfate (SDS), urea, NaN₂, β-mercaptoethanol, and EDTA had different degrees of inhibition on enzyme activity. The catalase from C. glutamicum shows high catalytic efficiency and high alkaline stability, suggesting its potential utilization in industrial production.

Flavonoids from the leaves of Astragalus membranaceus / 中成药

AIM To study the flavonoids from the leaves of Astragalus membranaceus (Fish.) Bge..METHODS The ethyl acetate and n-butyl alcohol fractions of 75％ ethanol extract from A.membranaceus leaves were isolated and purified by silica,ODS and preparative HPLC column,then the structures of obtained compounds were identified by spectral data.RESULTS Thirteen compounds were isolated and identified as quercetin (1),quercetin-3-O-β-D-glucopyranoside (2),rhamnocitrin-3-O-β-D-glucopyranoside (3),rhamnocitrin-3-O-β-neohesperidoside (4),rhamnocitrin-3-O-3-D-glucopyranoside (1'''→2'')-β-D-apiofuranosyl (5),complanatuside (6),glycitein (7),4',7-dihydroxy-3-methoxy isoflavone (8),genistein (9),calycosin-7-O-β-D-glucopyranoside (10),genistin (11),glycitin (12),tiliroside (13).CONCLUSION Compounds 5,8,13 are isolated from genus Astragalus for the first time,and compound 2 is first isolated from this plant.