title: Identification of active elementary flux modes in mitochondria using selectively permeabilized CHO cells.
abstract: Metabolic compartmentation is a key feature of mammalian cells. Mitochondria are the powerhouse of eukaryotic cells, responsible for respiration and the TCA cycle. We accessed the mitochondrial metabolism of the economically important Chinese hamster ovary (CHO) cells using selective permeabilization. We tested key substrates without and with addition of ADP. Based on quantified uptake and production rates, we could determine the contribution of different elementary flux modes to the metabolism of a substrate or substrate combination. ADP stimulated the uptake of most metabolites, directly by serving as substrate for the respiratory chain, thus removing the inhibitory effect of NADH, or as allosteric effector. Addition of ADP favored substrate metabolization to CO2 and did not enhance the production of other metabolites. The controlling effect of ADP was more pronounced when we supplied metabolites to the first part of the TCA cycle: pyruvate, citrate, α-ketoglutarate and glutamine. In the second part of the TCA cycle, the rates were primarily controlled by the concentrations of C4-dicarboxylates. Without ADP addition, the activity of the pyruvate carboxylase-malate dehydrogenase-malic enzyme cycle consumed the ATP produced by oxidative phosphorylation, preventing its accumulation and maintaining metabolic steady state conditions. Aspartate was taken up only in combination with pyruvate, whose uptake also increased, a fact explained by complex regulatory effects. Isocitrate dehydrogenase and α-ketoglutarate dehydrogenase were identified as the key regulators of the TCA cycle, confirming existent knowledge from other cells. We have shown that selectively permeabilized cells combined with elementary mode analysis allow in-depth studying of the mitochondrial metabolism and regulation.
authors.affiliation: Universität des Saarlandes, Technische Biochemie, Campus A 1.5, Saarbrücken D-66123, Germany.
authors.forename: Averina
authors.initials: A
authors.lastname: Nicolae
authors.affiliation: Universität des Saarlandes, Technische Biochemie, Campus A 1.5, Saarbrücken D-66123, Germany.
authors.forename: Judith
authors.initials: J
authors.lastname: Wahrheit
authors.affiliation: Universität des Saarlandes, Technische Biochemie, Campus A 1.5, Saarbrücken D-66123, Germany.
authors.forename: Yannic
authors.initials: Y
authors.lastname: Nonnenmacher
authors.affiliation: Universität des Saarlandes, Technische Biochemie, Campus A 1.5, Saarbrücken D-66123, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Weyler
authors.affiliation: Universität des Saarlandes, Technische Biochemie, Campus A 1.5, Saarbrücken D-66123, Germany. Electronic address: e.heinzle@mx.uni-saarland.de.
authors.forename: Elmar
authors.initials: E
authors.lastname: Heinzle
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D016466:CHO Cells / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002951:Citrates / Q000378:metabolism; D002952:Citric Acid Cycle; D006224:Cricetinae; D003412:Cricetulus; D007521:Isocitrate Dehydrogenase / Q000378:metabolism; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D008928:Mitochondria / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D010085:Oxidative Phosphorylation; D019289:Pyruvic Acid / Q000378:metabolism
chemical_list: D000596:Amino Acids; D002951:Citrates; D009243:NAD; D002245:Carbon Dioxide; D000244:Adenosine Diphosphate; D019289:Pyruvic Acid; D007521:Isocitrate Dehydrogenase; D007655:Ketoglutarate Dehydrogenase Complex
keywords: CHO cells; Elementary mode analysis; Mammalian metabolism; Mitochondria; Permeabilized cells; Tricarboxylic acid cycle