CHARACTERIZATION OF PHYTASE PRODUCED BY ASPERGILLUS-NIGER

The extracellular activity of Aspergillus niger phytase at the end of the growth phase was 132 nkat/mL in a laboratory bioreactor. The purif ied enzyme has molar mass approximately 100 kDa, pH optimum at 5.0, te mperature optimum at 55 degrees C and high pH and temperature stabilit y. The K-m for dodecasodium phytate, calcium phytate and 4-nitrophenyl phosphate are 0.44, 0.45 and 1.38 mmol/L, respectively. The enzyme is noncompetively inhibited by inorganic monophosphate (K-i = 2.85 mmol/ L) and by Cu2+, Zn2+, Hg2+, Sn2+, Cd2+ ions and strongly by F- ones; i t is activated by Ca2+, Mg2+ and Mn2+ ions. The substrate specificity of phytase is broad with the highest affinity to calcium phytate.