title: Metabolic flux analysis in complex isotopolog space. Recycling of glucose in tobacco plants.
abstract: Tobacco plants grown in vitro were supplied with a mixture of [U-13C6]glucose and unlabelled sucrose via the root system. After 20 days, leaves were harvested and extracted with water. Glucose was isolated from the extract and was analysed by 13C NMR spectroscopy. All 13C signals appeared as complex multiplets due to 13C-13C coupling. The abundance of 21 isotopologous glucose species was determined from the 13C NMR signal integrals by numerical deconvolution using a genetic algorithm. The relative fractions of specific isotopologs in the overall excess of 13C-labelled specimens establish flux contributions via glycolysis/glucogenesis, pentose phosphate pathway, citric acid cycle and Calvin cycle including 13CO2 refixation. The fluxes were modelled and reconstructed in silico by a novel rule-based approach yielding the contributions of circular pathways and the degree of multiple cycling events. The data indicate that the vast majority of the proffered [U-13C6]glucose molecules had been modified by catabolism and subsequent glucogenesis from catabolic fragments, predominantly via passage through the citric acid cycle and the pentose phosphate pathway.
authors.affiliation: Lehrstuhl für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Ettenhuber
authors.forename: Tanja
authors.initials: T
authors.lastname: Radykewicz
authors.forename: Waltraud
authors.initials: W
authors.lastname: Kofer
authors.forename: Hans-Ulrich
authors.initials: HU
authors.lastname: Koop
authors.forename: Adelbert
authors.initials: A
authors.lastname: Bacher
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Eisenreich
mesh_terms: D000465:Algorithms; D002244:Carbon / Q000378:metabolism; D002247:Carbon Isotopes; D005947:Glucose / Q000737:chemistry / Q000378:metabolism*; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D018515:Plant Leaves / Q000737:chemistry / Q000378:metabolism; D014026:Nicotiana / Q000737:chemistry / Q000378:metabolism*; D003313:Zea mays / Q000737:chemistry / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D002244:Carbon; D005947:Glucose