Aspergillus Niger Phytase: Purification and Characterization

ABSTRACT

An extracellular phytase from a wild type Aspergillus niger was purified in three steps by using ultrafiltration through a PS 50 membrane, Sephadex G-100 and DEAE-Sepharose CL 6B column chromatographies. The single protein band on SDS-PAGE suggested that the enzyme was homogeneous. The molecular weight determined from the SDS-PAGE was 39 kDa. Phytase had two pH optima—at pH 2.62 and pH 5.05 with temperature optima at 55 and 58 °C respectively. The enzyme proved to be fairly specific for phytate, and the kinetic parameters for hydrolysis of sodium phytate were Km 0.929 μM and Vmax 52.36 nkat/cm³. Some metal ions such as Ba²⁺ and Ca²⁺ stimulated phytase activity at concentrations of 100 nmol but it was greatly inhibited ions of Hg, Cu, Zn, Fe, Al. Enzyme reveals the phenomenal property to be activated by the ions of the heavy metals Pb an Ag. The unique properties of the wild type phytase give it some advantages for its applications.