Figure 4.

Effects of pH on fucoidanase activity (a) and stability. (b) Effects of pH on fucoidanase activity was determined under the following method: 1.0 mL substrate solution (pH 3–8) in buffer solutions (50 mmol·L⁻¹ sodium citrate buffer, 50 mmol·L⁻¹ sodium phosphate buffer, 50 mmol·L⁻¹ sodium carbonate buffer) was added to 0.1 mL enzyme solution and then was incubated at 50°C for 10 min. The pH stability of the enzyme was determined by assaying the residual activity after incubating enzyme for 3 h at the room temperature at different pH levels ranging from 3 to 9. Residual fucoidanase activity was determined by adding 0.1 mL enzyme solution to 1.0 mL of substrate solution (citric acid-citric sodium buffer, pH 6.0) and then was incubated at 50°C for 10 min.