FIG. 6.

Metabolic fluxes in autotrophically (CO₂ and H₂) grown cells (A), in cells grown in the presence of acetate (acetate plus CO₂ and H₂) (B), and in cells grown in the presence of succinate or 4-hydroxybutyrate (succinate or 4-hydroxybutyrate plus H₂ and CO₂) (C). Sulfur serves as the electron acceptor in anaerobic respiration. The shaded arrows indicate junctions of organic substrates with the central carbon metabolism. The open arrows symbolize metabolic fluxes away from central carbon metabolites to building blocks. The numbers (given as percentages) refer to 100% metabolic fluxes to the central intermediates from which all building blocks are made. Numbers in open arrows and squares are percentages of total biosynthetic fluxes that start from the central metabolites acetyl-CoA, pyruvate, etc. Numbers in ovals are percentages of metabolic fluxes that are required to supply 100% of the central metabolites. The scheme also shows how pyruvate feeds into this metabolic flux (without giving figures for the metabolic fluxes). The regulation of the enzyme activities under the different growth conditions reflects the biosynthetic demands quite well. For explanations, see the text.