Fig. 1.

Simplified metabolic network of the designed isobutanol-producing cells, optimized for anaerobic isobutanol synthesis. Pfl (encoded by the gene pflB), pyruvate formate lyase; PDHC (pdh), PDHC enzyme; AlsS_{B. subtilis} (alsS_{B. subtilis}), acetolactate synthase from B. subtilis. It should be noted that E. coli has the endogenous acetolactate synthase enzyme encoded by ilvHI, ilvGM, or ilvNB (http://www.ecocyc.org). Here, AlsS_{B. subtilis} is used to bypass the allosteric inhibition by valine (2, 21). IlvC (ilvC), 2,3-dihydroxy isovalerate oxidoreductase; IlvD (ilvD), 2,3-dihydroxy isovalerate dehydratase; Kivd_{L. lactis} (kivd_{L. lactis}), α-ketoacid decarboxylase from L. lactis; Adh2_{S. cerevisiae}, alcohol/aldehyde dehydrogenase from S. cerevisiae; AdhE, aldehyde/alcohol dehydrogenase from E. coli.