Figure 5.

Metabolite concentrations (N = 339) and quantitative errors observed in 20 E. coli extracts as measured by calibrated ITOCSY vs the established FMQ protocol.(1) Each extract was mixed 1-to-1 with a ¹³C-enriched E. coli extract. FMQ values were based on the intensities of ¹²C-specific spectra, whereas ITOCSY values were derived from ¹²C/¹³C ratios observed for metabolites in each mixture. Quantitative errors observed in these data were concentration-dependent; metabolites with concentrations ranging from 0.010 to 0.1, 0.1 to 0.5, 0.5 to 1, and 1 to 11 mM showed average absolute errors of 17, 13, 8, and 4%, respectively. A total of 24 compounds were quantified in this study; glucose, glutamine, isoleucine, MES, phenylalanine, and trehalose were excluded from the figure because these compounds were not observable in ITOCSY spectra of the ¹³C-enriched library. A complete list of metabolite concentrations observed in the E. coli extracts can be found in Supporting Information Table S-2.