title: Evidence for transketolase-like TKTL1 flux in CHO cells based on parallel labeling experiments and (13)C-metabolic flux analysis.
abstract: The pentose phosphate pathway (PPP) is a fundamental component of cellular metabolism. It provides precursors for the biosynthesis of nucleotides and contributes to the production of reducing power in the form of NADPH. It has been hypothesized that mammalian cells may contain a hidden reaction in PPP catalyzed by transketolase-like protein 1 (TKTL1) that is closely related to the classical transketolase enzyme; however, until now there has been no direct experimental evidence for this reaction. In this work, we have applied state-of-the-art techniques in (13)C metabolic flux analysis ((13)C-MFA) based on parallel labeling experiments and integrated flux fitting to estimate the TKTL1 flux in CHO cells. We identified a set of three parallel labeling experiments with [1-(13)C]glucose+[4,5,6-(13)C]glucose, [2-(13)C]glucose+[4,5,6-(13)C]glucose, and [3-(13)C]glucose+[4,5,6-(13)C]glucose and developed a new method to measure (13)C-labeling of fructose 6-phosphate by GC-MS that allows intuitive interpretation of mass isotopomer distributions to determine key fluxes in the model, including glycolysis, oxidative PPP, non-oxidative PPP, and the TKTL1 flux. Using these tracers we detected a significant TKTL1 flux in CHO cells at the stationary phase. The flux results suggest that the main function of oxidative PPP in CHO cells at the stationary phase is to fuel the TKTL1 reaction. Overall, this study demonstrates for the first time that carbon atoms can be lost in the PPP, by means other than the oxidative PPP, and that this loss of carbon atoms is consistent with the hypothesized TKTL1 reaction in mammalian cells.
authors.affiliation: Department of Chemical and Biomolecular Engineering, Metabolic Engineering and Systems Biology Laboratory, University of Delaware, Newark, DE 19716, USA.
authors.forename: Woo Suk
authors.initials: WS
authors.lastname: Ahn
authors.affiliation: Department of Chemical and Biomolecular Engineering, Metabolic Engineering and Systems Biology Laboratory, University of Delaware, Newark, DE 19716, USA.
authors.forename: Scott B
authors.initials: SB
authors.lastname: Crown
authors.affiliation: Department of Chemical and Biomolecular Engineering, Metabolic Engineering and Systems Biology Laboratory, University of Delaware, Newark, DE 19716, USA. Electronic address: mranton@udel.edu.
authors.forename: Maciek R
authors.initials: MR
authors.lastname: Antoniewicz
mesh_terms: D000818:Animals; D016466:CHO Cells; D066241:Carbon-13 Magnetic Resonance Spectroscopy / Q000379:methods*; D003198:Computer Simulation; D003412:Cricetulus; D020869:Gene Expression Profiling / Q000379:methods*; D007553:Isotope Labeling / Q000379:methods; D008657:Metabolic Clearance Rate / Q000502:physiology; D064688:Metabolic Flux Analysis / Q000379:methods*; D008954:Models, Biological; D010427:Pentose Phosphate Pathway / Q000502:physiology*; D014174:Transketolase / Q000235:genetics / Q000378:metabolism*
chemical_list: C505431:TKTL1 protein, human; D014174:Transketolase
keywords: Isotopic tracers; Metabolic model validation; Pentose phosphate pathway; TKTL1; Transketolase