Extracellular phytase from Aspergillus niger CFR 335: purification and characterization

Phytase, that is extensively used as a feed additive is capable of hydrolyzing phytic acid, an antinutrient found in about 60-80 % of all the plant commodities. This enzyme improves the bioavailability of essential minerals such as Ca2+, Mg2+, P, Zn2+, Fe3+, that are bound to phytic acid. An extracellular phytase from a local fungal isolate, Aspergillus niger CFR 335 was purified to homogeneity through a three-step column chromatography using DEAE-Sephadex anion exchanger. An active fraction of the enzyme was obtained with NaCl gradient of 2.5 M in DEAE Sephadex column. The enzyme was purified up to 16 fold with a yield of 28.5 %. Substrate specificity studies revealed a highest specific activity of 32.6 +/- 3.1 U/mg for sodium phytate with the K-m value of 0.08 +/- 0.1 mM. The molecular weight of the enzyme was 66 kDa with an optimum temperature of 30 degrees C and pH 4.5. Up to 80 % of the activity was retained even after storing the enzyme for 6 months at 4 degrees C.