Metabolic quantitative protein abundance

Intracellular fluxes can be estimated more precisely through 13C tracer experiments. Following 13C feeding to a cell it is possible to analyze metabolic products, such as amino acids, and measure 13C enriched patterns, so to be able to reconstruct the flux distribution from the measured data [91]. To obtain flux data from the labeling patterns, two techniques can be applied NMR [92, 93] and MS [94, 95]. Due to the low intracellular concentration of metabolites, these are often difficult to measure therefore the analysis of the labeling pattern of amino acids in proteins is used as input for flux quantification. Here proteins are hydrolyzed to release labeled amino acids and further analyzed by NMR of GC-MS. Once NMR or MS spectra are recorded, the next step is the quantitative interpretation of the isotopomer data by using mathematical models that describe the relationship between fluxes and the observed isotopomer abundance [96, 97], Some of the mathematical approaches used include cumulative isotopomer (cumomers) [98], bondomers [99], and fractional labeling [100], For a more comprehensive review on the methods we refer to Sauer [91]. 

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