Enzymatic Characterization of a Novel Acid and Thermostable Phytase from Aspergillus nidulans

To purify a single heat and acid-resistant phytase from Aspergillus nidulans AnP-16 and to characterize the enzyme in order to provide theoretical basis for its application in food industry. Phytase was purified by ammonium sulfate fractional precipitation,ion exchange chromatography and hydrophobic chromatography,and its molecular weight was determined by sds-page electrophoresis. Results showed that,this phytase was purified to homogeneity with 60.8 fold purification and 41.6% recovery yield. The molecular mass of the enzyme was estimated as about 52 kDa. The purified phytase had an optimal activity at 55 ℃ and pH4.0,and it exhibited high enzymatic activity between pH3.0 and 6.0. The enzyme retained more than 80% of its initial activity after being incubated under varying pH conditions(pH2.0~7.0)for 3 h. The purified phytase was resistant to heat inactivation,as it retained 81% of its initial activity after incubation at 70 ℃ for 1 h. The inhibition of phytase activity by metal ions was observed to be drastically inhibited by Hg²⁺,Mn²⁺,Fe²⁺,Cu²⁺ and Zn²⁺ at 5 mmol/L concentrations. A positive effect was obtained with Ca²⁺ and Mg²⁺ at 1 and 5 mmol/L,methanol and ethanol at 2% concentration. The acidic phytase activity was also inhibited by SDS while the other detergents(Triton X-100 and Tween 80)and solvents(acetone and isoamylol)had no obvious effect on its activity.The phytase displayed broad substrate specificity while the enzyme was more specific for sodium phytate and the K_m value for phytate was 0.576 mmol/L. Based on phytase’s resistance to acid and heat and broad substrate catalytic activity,it is expected to be applied in the field of grain,oil and food processing to improve the nutritional value of food.