Isolation,Purification and Characterization of Phytase from Recombinant Pichia pastoris E22

The phytase produced by the recombinant Pichia pastoris E22, which was constructed with the phytase gene from Aspergillus niger N14, was purified and characterized. The phytase had two optimum peaks at pH 2.5 and 5.5. Its optimum temperature, Km for sodium phytate and specific activity was 45 ℃, 0.000 2 mol/L and 493 328.7 u/mg at pH2.5 and 55 ℃, 0.000 1 mol/L and 624 376.2 u/mg at pH5.5. The activity of the phytase was reduced by Fe2+ at pH 2.5 and was reduced by Zn2+ and Cu2+ at pH 5.5. The remaining phytase activity after 10 minutes' incubation at 85 ℃, after 6 hours incubation with pepsin at pH2.5 and with trypsin at pH5.5 was about 70%, 95% and 85%, respectively. The molecule weight of the phytase was 61.7 KD and the isoelectric point was between pH4.5 and pH5.0.