Extracellular Phytase (E. C. 3.1.3.8) fromAspergillus FicuumNRRL 3135: Purification and Characterization

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Abstract
Extracellular phytase from Aspergillus ficuum, a glycoprotein, was purified to homogeneity in 3 column chromatographic steps using ion exchange and chromatofocusing. Results of gel filtration chromatography and SDS-polyacrylamide gel electrophoresis indicated the approximate molecular weight of the native protein to be 85–100-KDa. On the basis of a molecular weight of 85–KDa, the molar extinction coefficient of the enzyme at 280 nm was estimated to be 1.2 × 104 M-l cm-1. The isoelectric point of the enzyme, as deduced by chromatofocusing, was about 4.5. The purified enzyme is remarkably stable at 0°C. Thermal inactivation studies have shown that the enzyme retained 40% of its activity after being subjected to 68°C for 10 minutes, and the enzyme exhibited a broad temperature optimum with maximum catalytic activity at 58°C. The Km of the enzyme for phytate and p-nitrophenylphosphate is about 40 uM and 265 uM, respectively, with an estimated turnover number of the enzyme for phytate of 220 per sec. Enzymatic deglycosylation of phytase by Endoglycosidase H lowered the molecular weight of native enzyme from 85–100-KDa to about 76–KDa; the digested phytase still retained some carbohydrate as judged by positive periodic acid-Schiff reagent staining of the electrophoresed protein. Immunoblotting of the phytase with monoclonal antibody 7H10 raised against purified native enzyme recognized not only native but also partially deglycosylated protein.