||Bacteria Escherichia coli
||Bennett BD, Kimball EH, Gao M, Osterhout R, Van Dien SJ, Rabinowitz JD. Absolute metabolite concentrations and implied enzyme active site occupancy in Escherichia coli. Nat Chem Biol. 2009 Aug5(8):593-9 Table - link PubMed ID19561621
||P.594 right column top paragraph: "[Investigators] quantified metabolites by LC-MS/MS [Liquid chromatography-mass spectrometry] using an isotope ratio-based approach [ref 8]. As isotope-labeled standards for many metabolites are not available, [they] used uniformly 13C-labeled glucose medium to label the intracellular metabolome of E. coli [ref 25]. This enabled the use of commercially available unlabeled compounds as internal standards. As many metabolites can react in solution (for example, amines with carbonyl-containing compounds), [they] prepared metabolite standard mixtures freshly within 4 h of use and maintained them at -20°C. To minimize the risk of standard degradation, stock solutions were limited to single metabolites, stored at -80°C and used within 3 d of initial preparation from powder. [They] performed absolute quantitation of the cellular species by extracting labeled cells in the presence of unlabeled standards of known concentration. Internal standards were included directly in the quenching solvent. Thus, cellular metabolites and internal standards experienced similar opportunities for absorptive losses and degradation. As labeling of compounds that assimilate bicarbonate was found to be incomplete (Supplementary Tables 1 and 2), concentrations were corrected for incomplete labeling [ref 26] (see Methods). [They] used the extracts of cells grown in 13C-glucose as internal standards for quantifying the metabolome of E. coli grown on unlabeled glycerol and acetate."
||Abstract: "The total observed intracellular metabolite pool was approximately 300 mM. A small number of metabolites dominate the metabolome on a molar basis, with glutamate being the most abundant."