Development of isotope monitoring methods provided a better
understanding regarding the configuration of isotopes and the
central carbon metabolic pathway. In this study, we presented a
methodology for 13C isotope distribution monitoring of 25 central
metabolites using GC/MS. Previous metabolomics research used
GC/MS to obtain a quantification of central metabolites using the
most abundant ion peaks. Therefore, many of the mass ions used
in those studies were not suitable in isotope monitoring, because
existence of structural isomers with the same mass disrupted intact
isotope pattern analysis. Therefore, all of the possible mass ions
of the 25 central carbon metabolites were re-examined to single
out proper monitoring mass ions that contain defined carbon
backbone information and are not contaminated by structural isomers.
Consequently, 34 monitoring mass ions for 25 intermediates
were selected and examined for isotope pattern analysis. Then, MIA
method was applied to analyze all selected mass ions in central carbon
metabolites. Natural isotopomer abundances of carbon central
metabolites obtained from the NIST database were concordant with
our experimental results; thus, they were used for data filtering
processes to compute isotope labeled fractions. As a result, isotope
labeled fractions of central metabolites were successfully monitored
for the first time using GC/MS. Finally, monitoring of isotope
patterns for intermediates was performed using selectedmass fragmentions
with a supplement of U-13C GLU to a microbial organism.
Surprisingly high level of partially labeled isotope fractions were
observed, which were originated frompentosephosphatepathway.
Up to now, isotope labeling pattern study of central carbon
metabolites using GC/MS has been limited, partly because mass
fragmentations of central carbon metabolites have not been thoroughly
investigated and a method to deal with relatively high level
of natural mass isotopomer has not been proposed. In this study,
the combination of selecting proper ion sets and MIA method
was proposed for monitoring labeling fractions of central carbon
metabolites. Especially MIA method was enabled due to the recent
development of MS database and firstly applied to ion peaks of
central carbon metabolites with GC/MS. The developed method
was extended to quantification of metabolites or to monitoring
isotope distributions in the metabolites. Because accurate determination
of isotope distribution and metabolite concentration is
required in metabolome-based 13C MFA, this approach can provide
an opportunity for improved understanding of carbon fluxes in
living organisms.