Fig. 4

a A schematic diagram presenting the promiscuous activities of xylose reductase (encoded by XYL1) and xylitol dehydrogenase (encoded by XYL2) on galactose and galactitol, respectively. b The oxidoreductive pathway and Leloir pathway for galactose catabolism. Normalized abundance levels of the intracellular metabolites of S. cerevisiae strain EJ4 grown on galactose (GAL), glucose (GLC), xylose (XYL), or cellobiose (CB) related to the galactose catabolism are shown in the box-whisker plots. The x-axis labels in the box-whisker plots represent the four different carbon sources with two different sampling timepoints, 1, mid-exponential phase; 2, late-exponential phase