Purification and characterization of a highly selective glycyrrhizin-hydrolyzing β-glucuronidase from Penicillium purpurogenum Li-3

A novel β-glucuronidase from filamentous fungus Penicillium purpurogenum Li-3 was purified to electrophoretic homogeneity by ultrafiltration, ammonium sulfate precipitation, DEAE-cellulose ion exchange chromatography, and Sephadex G-100 gel filtration with an 80.7-fold increase in specific activity. The purified β-glucuronidase is a dimeric protein with an apparent molecular mass of 69.72 kDa (m/z = 69,717), determined by MALDI/TOF-MS. The optimal temperature and pH of the purified enzyme are 40 °C and 6.0, respectively. The enzyme is stable within pH 5.0-8.0, and the temperature up to 45 °C. Mg²⁺ ions enhanced the activity of the enzyme, Ca²⁺ and Al³⁺ showed no effect, while Mn ²⁺, Zn²⁺, Hg²⁺ and Cu²⁺ substantially inhibited the enzymatic activity. The K_m and V _max values of the purified enzyme for glycyrrhizin (GL) were evaluated as 0.33 mM and 59.0 mmol mg^-1 min^-1, respectively. The purified enzyme displayed a highly selective glycyrrhizin-hydrolyzing property and converted GL directly to glycyrrhetic acid mono-glucuronide (GAMG), without producing byproduct glycyrrhetic acid (GA). The results suggest that the purified enzyme may have potential applications in bio-pharmaceutical and biotechnological industry.