Thermostability studies of phytase. The protein was incubated at 80 °C in the absence or presence of metal ions (Cu²⁺ or Fe³⁺) separately in 50 mM acetate buffer at pH 6. Unfilled circles shows the stability in the absence of any metal ion, while filled circles and unfilled triangles shows the stability in the presence of Fe³⁺ and Cu²⁺, respectively.