(13)C mass isotopomer analysis of the TCA cycle by ion trap GC-M

Isotopic tracers have been used for several years to study intermediary metabolism. As FT-NMR and GC-MS analytical techniques become more advanced, metabolic studies using stable isotope labeled tracers ($sp{13}$C, $sp{15}$N, and $sp{18}$O) are becoming more popular. By studying the degree and position of stable isotope label incorporation, information about the metabolic process being investigated may be deduced. Many research studies on intermediary metabolism have been conducted using either GC-MS or $sp{13}$C NMR to learn about the biochemical processes occurring in the TCA cycle. Each analytical technique gives different, but complementary, information about the system being investigated. Few studies have compared the metabolic information obtained by the individual analytical techniques. This report details a comparison of the physiological parameters obtained by application of a mathematical model of the TCA cycle to data from each technique. The mathematical model relating the $sp{13}$C NMR multiplet information from $sp{13}$C-enriched glutamate to the underlying cellular metabolism was previously developed by F. M. H. Jeffrey et al.$sp1$ This report also details the modification of the mathematical model to incorporate a tandem MS (or MS/MS) to perform mass isotopomer analysis for the study of cellular metabolism is reported. The metabolic parameters obtained by GC-MS and GC-MS/MS analysis agreed well with those obtained by $sp{13}$C NMR analysis in three of the four case studies. The fourth case study involved a more complex metabolic situation. Metabolic parameters based on data obtained from both techniques agreed well on all but two parameters.