Figure 3.

Effect of temperature and pH. A. Temperature optimum and stability. B. pH optimum and stability. Temperature and pH optimum (■) and stability (□) of Nk from B. subtilis VTCC-DVN-12-01. For temperature and pH optimum, the activity of 0.6 μg of Nk was measured with 1 mM Suc-AAPF-pNA as a substrate at pH 8 and various temperatures 30-70°C and at 65°C and various pH 5 to 11, respectively. For thermal and pH stability, 0.6 μg of Nk was incubated in 50 mM Na-phosphate buffer at various temperatures 30-70°C for 1 h and in 50 mM acetate (pH 5), phosphate (pH 6–8) and Tris–HCl (pH 9–11) at 30°C for 1 h, respectively. The residual activity was determined at pH 9 and 65°C with 1 mM Suc-AAPF-pNA as a substrate.