FIG 5.

Flux partitioning around valine and leucine metabolism. The distributions of fluxes around the α-ketoisovalerate and α-ketoisocaproate nodes, which are the main intermediates of both the catabolism and the anabolism of leucine and valine, were investigated through stable isotope tracer experiments with ¹³C-labeled valine and ¹³C-labeled leucine. (A and D) Portions of consumed (cons) valine (A) and leucine (D) recovered in proteinogenic (prot) leucine and valine. The labeled fraction (light color) corresponds to consumed valine or leucine directly incorporated into proteins, while the unlabeled fraction (dark color) represents the proteinogenic amino acids synthesized de novo from CCM precursors. (B and E) Portions of consumed valine (B) or leucine (E) converted into higher alcohols (isoamyl alcohol and isobutanol). The labeled fraction (light color) corresponds to the fraction of higher alcohol synthesized using the carbon backbone from consumed valine or leucine; the unlabeled fraction (dark color) represents the part of volatile molecules synthesized from CCM α-keto acids. Isotopic enrichments (defined as the molar ratio of the quantity of labeled compound to the total quantity of compound) are shown above each bar. The raw data and details of the calculations are provided in the supplemental material. (C and F) Partitioning of fluxes involved in the use of valine (C) or leucine (F) during fermentation. The fraction of consumed valine or leucine catabolized through a pathway, reported in the colored boxes, was assessed from the molar ratio of the amount of a labeled proteinogenic amino acid or volatile compound to the total amount of consumed amino acid. ic, intracellular.