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 65.5kDa in gel filtration and SDS-PAGE. It possessed an optimal pH of 1.3 and an optimal temperature of 67 degrees C, and manifested a K(m) of 0.295mM and a V(max) of 55.9nmol (phosphate)/min. Phytase activity was not significantly affected by metal ions such as Ca(2+), Mg(2+), Mn(2+), Zn(2+), but was slightly stimulated in the presence of EDTA. The phytase was stable at 60 degrees C with no obvious loss of activity upon its incubation at 70 degrees C for 20min. 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.