title: Modeling framework for isotopic labeling of heteronuclear moieties.
abstract: BACKGROUND
  Isotopic labeling is an analytic technique that is used to track the movement of isotopes through reaction networks. In general, the applicability of isotopic labeling techniques is limited to the investigation of reaction networks that consider homonuclear moieties, whose atoms are of one tracer element with two isotopes, distinguished by the presence of one additional neutron.
  
  
  RESULTS
  This article presents a reformulation of the modeling framework for isotopic labeling, generalized to arbitrarily large, heteronuclear moieties, arbitrary numbers of isotopic tracer elements, and arbitrary numbers of isotopes per element, distinguished by arbitrary numbers of additional neutrons.
  
  
  CONCLUSIONS
  With this work, it is now possible to simulate the isotopic labeling states of metabolites in completely arbitrary biochemical reaction networks.
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 3335 Innovation Boulevard, Richland, WA 99354 USA.
authors.forename: Mark I
authors.initials: MI
authors.lastname: Borkum
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 3335 Innovation Boulevard, Richland, WA 99354 USA.
authors.forename: Patrick N
authors.initials: PN
authors.lastname: Reardon
authors.affiliation: Biological Sciences Division, Pacific Northwest National Laboratory, 3335 Innovation Boulevard, Richland, WA 99354 USA.
authors.forename: Ronald C
authors.initials: RC
authors.lastname: Taylor
authors.affiliation: Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 3335 Innovation Boulevard, Richland, WA 99354 USA.
authors.forename: Nancy G
authors.initials: NG
authors.lastname: Isern
keywords: Cumomers; Elementary metabolite units; Isotopic labeling; Isotopomers; Metabolic engineering