Enzymatic properties of wild-type XynAS9 and its mutants. (A) pH-dependent activity profiles; (B) pH stability; (C) temperature-dependent activity profiles; (D) enzyme inactivation at different temperatures. Symbols: □, wild-type XynAS9; ●, V81P mutant; ○, G82E mutant; -, V81P/G82E mutant; ■, D185P/S186E mutant; ▲,V81P/G82E/D185P/S186E mutant.