Abstract:
Phytase, an enzyme that catalyzes the stepwise hydrolysis of
myo-inositol-1,2,3,4,5,6-hexakisphosphate (phytate) into phosphorous and organophosphate
compound and capable of reducing environmental pollution and metal chelating effect of
phytate, was purified from Aspergillus fumigatus isolated from African Giant Snail (Achatina
fulica); a member of class gastropoda and a macrophytophagus herbivore; that feeds on a
wide variety of plants and decaying materials. Phytase isolated from Aspergillus fumigatus
was subjected to ammonium sulphate precipitation, followed by ion exchange
chromatography (DEAE Sephacel) and then gel filtration (Sephacryl S-200). Effect of pH and
Temperature on the activity and stability of the purified phytase were determined, while
effects of metal ions, chemical inhibitors, molecular weight and kinetic parameters were also
investigated. Approximately 45%- fold purification was achieved with an overall recovery of
15%. The physicochemical properties revealed that the purified phytase has an optimum
temperature activity at 40oC and it retained 80 % of its initial activity after 1 hour incubation
period at 50oC and maintained about 100% stability at pH 5.0 after 6 hours with over 80%
remaining activity between pH 4-7. The kinetic parameters of the purified enzyme, Vmax and
Km were determined to be 35.7 μmol/min and 7.2 mM respectively. The phytase activity was
enhanced in the presence of Ca2+, Cu2+ and Fe2+, while EDTA also enhanced enzymatic
activity at low concentration but was greatly inhibited by Zn2+, Hg2+ and Al3+, Sodium
Dodecyl Sulphate (SDS) and urea. The result showed that phytase produced from A.
fumugatus may contribute significantly to the phytate degrading enzyme system in African
giant snail and may serve a useful commercial purpose.
