Time profiles of absolute concentrations and relative 13C-enrichments of the 13C-labeled metabolites after addition of [U13C]glucose (40 mM) at different time points. (a) Lactate (blue), acetate (red), propionate (green), butyrate (purple), and (b) isobutyrate concentrations. Solid colours show the absolute concentration measured in the samples. Stripes highlight the relative enrichment of 13C (presented as atom percent excess, APE) in the metabolites after labeling with [U13C]glucose, with percentages indicated. Average of duplicates is shown. % = atom%-excess (APE).