Purification, characterization, and cloning of a novel phytase with low pH optimum and strong proteolysis resistance from Aspergillus ficuum NTG-23

A novel phytase was isolated from Aspergillus ficuum NTG-23 with a procedure involving ion-exchange chromatography on DEAE-cellulose, CM-cellulose and FPLC-gel filtration on Superdex 75. The protein exhibited a molecular mass of 65.5 kDa in gel filtration and SDS–PAGE. It possessed an optimal pH of 1.3 and an optimal temperature of 67 °C, and manifested a Km of 0.295 mM and a Vmax of 55.9 nmol (phosphate)/min. Phytase activity was not significantly affected by metal ions such as Ca2+, Mg2+, Mn2+, Zn2+, but was slightly stimulated in the presence of EDTA. The phytase was stable at 60 °C with no obvious loss of activity upon its incubation at 70 °C for 20 min. The enzyme exhibited a broad substrate selectivity and showed strong resistance toward pepsin and trypsin. The unique properties suggest that the phytase has the potential to be useful as an animal feed supplement.