Figure 4. Effect of pH and temperature on MetaChi18A activity and stability. Chitinolytic activity was determined using 0.2 mg/mL of 4-MUF derivatives (A and B orange slashed line, Y-axis on the right) and 10 mg/mL of colloidal chitin (A and B dark blue line, Y-axis on the left) as substrate. Enzyme concentration was 0.40 and 100 ng/µL, respectively. A, Effect of pH on the activity for 30 min at 37°C; B, effect of temperature on the activity for 30 min at pH 5; C, stability of MetaChi18A incubated at indicated pH for 1 or 24 h without substrate; D, stability of MetaChi18A incubated at the indicated temperature for 1, 3, or 24 h without substrate. The remaining activities were measured for 30 min at 37°C and pH 5 using 10 mg/mL of colloidal chitin. The reactions were performed in 25 mM buffers: pH 3 sodium citrate; pH 4 and 5 sodium acetate; pH 6 and 7 sodium phosphate; pH 8 and 9 Tris-HCl; pH 10 and 11 sodium carbonate. Error bars represent standard deviation. One unit of chitinase activity (U) was defined as the release of 1 µmol of reducing sugar or 4-MUF per minute.