A schematic view of the joint metabolic and gene regulation network model of AB fermentation in C. acetobutylicum. Acids are outlined in red and solvents in blue. The AB fermentation is characterized by a bi-phase metabolism. Following glycolysis the cells produce either the acids acetate (A) and butyrate (B) at a high pH, or the solvents acetone (An) and butanol (Bn) at a low pH while ethanol (En) is made in both phases but at a relatively low level. A characteristic reaction in this metabolism is the conversion of acetate (or butyrate) and acetoacetyl-CoA into acetyl-CoA (or butyryl-CoA) and acetoacetate, this being the first step in the formation of solvents from acids. We reduced the metabolic network published in  to ten reactions R
found in Table 1. For reactions R3, R5, R6, R7, and R10 we include gene regulation for the enzymes which are involved in the production of the solvents.