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.