Analysis of Kinetic Labeling of Amino Acids and Organic Acids by GC-MS

Plant metabolic pathways and the molecular and atomic fluxes through them can be deduced using stable isotopically labeled substrates. To this end one prerequisite is accurate measurement of the labeling pattern of targeted metabolites. Experiments are generally limited to the use of single-element isotopes, mainly ¹³ C. Here, we summarize the application of gas chromatography-time of flight mass spectrometry (GC-TOF-MS) for metabolic studies using differently labeled elemental isotopes applied to both intact organelles and whole plant tissue. This method allows quantitative evaluation of a broad range of metabolic pathways without the need for laborious (and potentially inaccurate) chemical fractionation procedures commonly used in the estimation of fluxes following incubation in radiolabeled substrates. We focus herein on the determination of isotope labeling in organic and amino acids.