Effects of reaction conditions on xylanase catalytic activity. a The effect of pH. The interconnected points represent the following buffers at a final concentration of 50 mM: acetate (pH 4.5–5.5); phosphate (5.5–6.5), MOPS (pH 6.5–7.5) and arginine-NaOH (pH 9.0). b The effect of temperature. The symbols in both graphs are filled square, parental XynA; filled circle, 2091A chimera and filled triangle 2621B chimera.