2.7 Determination of optimal pH and temperature on enzyme activity
The optimal pH value for enzyme activity was assayed in 50 mM citric acid-sodium dihydrogen phosphate buffer (pH 4.0 to 8.0) at 30°C. The optimal temperature was determined between 20°C and 50°C in buffer (pH 6.0). To determine thermostabilities, the purified enzyme of WT and mutants were incubated at 45°C. The samples were taken every 20 min, and then the residual activity of WT and mutants after different incubation time was performed as described above. The original activity before incubating at 45°C was taken as 100%. Each assay was repeated three times.