title: Purification and characterisation of an extracellular phytase from Aspergillus niger 11T53A9.
abstract: An extracellular phytase from Aspergillus niger 11T53A9 was purified about 51-fold to apparent homogeneity with a recovery of 20.3% referred to the phytase activity in the crude extract. Purification was achieved by ammonium sulphate precipitation, ion chromataography and gel filtration. The purified enzyme behaved as a monomeric protein with a molecular mass of about 85 kDa and exhibited maximal phytate-degrading activity at pH 5.0. Optimum temperature for the degradation of phytate was 55°C. The kinetic parameters for the hydrolysis of sodium phytate were determined to be KM = 54 µmol l(-1) and kcat = 190 sec(-1) at pH 5.0 and 37°C. The purified enzyme was rather specific for phytate dephosphorylation. It was shown that the phytase preferably dephosphorylates myo-inositol hexakisphosphate in a stereospecific way by sequential removal of phosphate groups via D-Ins(1,2,4,5,6)P5, D-Ins(1,2,5,6)P4, D-Ins(1,2,6)P3, D-Ins(1,2)P2 to finally Ins(2)P.
authors.affiliation: Department of Food and Bio Process Engineering, Max Rubner-Institute, Federal Research Institute of Nutrition and Food, Haidund-Neu-Straβe 9 , D-76131 Karlsruhe , Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Greiner
authors.forename: Lucineia Gomes
authors.initials: LG
authors.lastname: da Silva
authors.forename: Sonia
authors.initials: S
authors.lastname: Couri
keywords: Aspergillus niger; phytase; phytate; phytate-degrading enzyme
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