Isotopomer analysis using GC-MS

Knowledge of the complete isotopomer distribution represents the ultimate amount of information on the labeling pattern of a metabolite. One technique for measuring the isotopomer distributions is the analysis of the multiplet intensities arising from the 13C-13C couplings in NMR spectroscopy. While this technique has proven to be very valuable in the elucidation of labeling patterns of C2 and C3 units of various amino acids, fragments larger than C3 are very difficult to measure. Another technique, GC-MS, offers a unique possibility of analyzing fragments larger than C3 and GC-MS is therefore able to give information which is complementary to the information that can be obtained from NMR spectroscopy. In this work we have developed fast, simple, and robust GC-MS methods that can be used to gain information on the labeling patterns of the amino acids in a crude biomass hydrolysate. It is shown that a combination of information obtained from these analyses and information from the NMR spectroscopy is able to yield a much more complete picture of the isotopomer distributions of the amino acids than any of the two techniques alone. The GC-MS method was used for analyzing the labeling patterns of amino acids from a batch cultivation of Penicillium chrysogenum grown on fully labeled glucose. The data from this analysis showed no signs of any significant carbon isotope effects, and the measurements can therefore be used without corrections for metabolic flux analysis.