Fig. 2.

Effects of galactose on wild-type enzyme (square) and Y364F mutant (solid circle). Reactions catalyzed by wild-type and mutant enzymes were performed in citrate/phosphate buffer (0.1 M, pH 5.2) containing 0.25% oNPG with varying concentrations of galactose (from 0 to 90 mg/ml). The remaining activity was defined as the relative value of β-galactosidase activity measured with galactose to the maximum activity measured without galactose. The respective β-galactosidase activity of each protein (200 µg/ml protein, 36.2 U/ml for wild-type enzyme and 38.4 U/ml for Y364F mutant) measured without galactose was defined as 100%. Data represent the means of three experiments, and error bars represent the standard deviation