Preparation of baicalein from baicalin using a baicalin-β-D-glucuronidase from Aspergillus niger b.48 strain

摘要

Baicalin-beta-D-glucuronidase was produced from a culture of Aspergillus niger b.48 strain using Scutellaria root extract as an enzyme inducer, purified and characterized. The enzyme's molecular weight was approximately 45 kDa; its optimal operating temperature and pH were 50 degrees C and 5.0, respectively. The enzyme specifically hydrolysed 7-O-beta-D-glucuronide of baicalin into baicalein, weakly hydrolysed beta-D-glucuronide of p-nitrophenyl-beta-D-glucuronide and p-phenolphthalein-j3-D-glucuronide, but did not hydrolyse beta-D-glucuronide of glycyrrhizin. The Michaelis constant (Km) was 21.74 mM; Vmax was 11.63 mM/h. Common metallic ions almost did not effect enzyme activity; greater than 10 mM/L Cu2+ and greater 50 mM/L Fe3+ ion strongly inhibited enzyme activity. The use of pure enzyme in baicalin conversion to baicalein was costly, the crude baicalin-beta-D-glucuronidase from A. niger b.48 strain was used in the preparation of baicalein from baicalin to keep costs low. The optimum conditions for baicalein production from crude enzyme reaction were 1% baicalin reacting for 20 h-24 h at pH 5.0 and 50 degrees C. Here, 10.7 g baicalein was obtained from 20 g baicalin using the crude enzyme, and the molar yield was 88.4 %. Therefore, active baicalein was successfully produced at low cost from baicalin using a nontransgenic crude enzyme from A. niger b.48.