Effect of pH on enzyme activity. Activity was measured at 30°C for 30 min at the indicated pHs in 100 mM each buffer: Na-acetate (pH 4.0 to 6.0, closed rhombuses), Na-phosphate (pH 6.0 to 8.0, closed squares) and Tris-HCl (pH 8.0 to 9.0, closed triangles). The highest activity was taken as 100%. Reaction substrate was 0.25% red debranched arabinan. (a) Optimal reaction pH of AbnZ2. (b) Optimal reaction pH of AbnZ3.