Biochemical characterisation of extracellular phytase (myo-inositol hexakisphosphate phosphohydrolase) from a hyper-producing strain of Aspergillus niger van Teighem.
Aspergillus niger van Teighem, isolated in our laboratory from samples of rotten wood logs, produced extracellular phytase having a high specific activity of 22,592 units (mg protein)-1 . The enzyme was purified to near homogeneity using ion-exchange and gel-filtration chromatography. The molecular properties of the purified enzyme suggested the native phytase to be oligomeric, with a molecular weight of 353 kDa, the monomer being 66 kDa. The purified enzyme exhibited maximum activity at pH 2.5 and 52-55 degrees C. The enzyme retained 97% activity after a 24-h incubation at 55 degrees C in the presence of 10 mM glycine, while 87% activity was retained when no thermoprotectant was added. Phytase activity was not affected by most metal ions, inhibitors and organic solvents. Non-ionic and cationic detergents (0.1-5%) stabilise the enzyme, while the anionic detergent (SDS), even at a 0.1% level, severely inhibited enzyme activity. The chaotropic agents guanidinium hydrochloride, urea, and potassium iodide (0.5-8 M), significantly affected phytase activity. The maximum hydrolysis rate (Vmax) and apparent Michaelis-Menten constant (Km) were 1,074 IU/mL and 606 microM, respectively, with a catalytic turnover number of 3x10(5) s-1 and catalytic efficiency of 3.69x10(8) M-1 s-1.
Vats
Purva
P
Institute of Microbial Technology, Sector 39 A, Chandigarh, 160 036, India.
Banerjee
U C
UC
D010832:6-Phytase / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D001234:Aspergillus niger / Q000201:enzymology* / Q000254:growth & development; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D007218:Industrial Microbiology / Q000379:methods; D007700:Kinetics; D010833:Phytic Acid / Q000378:metabolism; D013696:Temperature; D015854:Up-Regulation
D010833:Phytic Acid; D010832:6-Phytase