Among many recombinant yeast strains currently available, we specifically choose S. cerevisiae 1400 (pLNH33) developed by Ho and coworkers (Krishnan et al., 1997). The strain was constructed by transforming the recombinant plasmids with two exogenous genes XYL1 and XYL2 (introduced from xylose-metabolizing Pichia stipitis), and one endogenous gene XKS1 (introduced from S. cerevisiae) into the host strain Saccharomyces yeast 1400 with high ethanol tolerance (Krishnan et al., 1997). The first two genes encode xylose reductase (XR) and xylitol dehydrogenase (XDH), which convert xylose to xylitol, and xylitol to xylulose, respectively, and the last one encodes xylulokinase (XK), which converts xylulose to xylulose-5-phophaste.

The HCM for the recombinant yeast 1400 (pLNH33) is presented below. The model has been previously developed by the authors (Song et al., 2009). The formulation of HCM is

composed of (i) construction of metabolic network, (ii) computation and selection of EMs, and (iii) parameter identification by model fitting.