Mass spectrometry in combination with tracer experiments based on
13C substrates can serve as a powerful tool for the modeling and
analysis of intracellular fluxes and the investigation of biochemical
networks. The theoretical background for the application of mass
spectrometry to metabolic flux analysis is discussed. Mass spectrometry
methods are especially useful to determine mass distribution of metabolites.
Additional information gained from fragmentation of metabolites,
e.g., by electron impact ionization, allows further localization
of labeling positions, up to complete resolution of isotopomer pools.
To effectively handle mass distributions in simulation experiments,
a matrix based general methodology is formulated. The natural isotope
distribution of carbon, oxygen, hydrogen and nitrogen in the target
metabolites is considered by introduction of correction matrices.
It is shown by simulation results for the central carbon metabolism
that neglecting natural isotope distributions causes significant
errors in intracellular flux distributions. By varying relative fluxes
into pentosephosphate pathway and pyruvate carboxylation reaction,
marked changes in the mass distributions of metabolites result, which
are illustrated for pyruvate, oxaloacetate, and alpha-ketoglutarate.
In addition mass distributions of metabolites are significantly influenced
over a broad range by the degree of reversibility of transaldolase
and transketolase reactions in the pentosephosphate pathway. The
mass distribution of metabolites is very sensitive towards intracellular
flux patterns and can be measured with high accuracy by routine mass
spectrometry methods. Copyright 1999 John Wiley & Sons, Inc.
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