title: 13C isotopomer analysis of glutamate by tandem mass spectrometry.
abstract: Tandem mass spectrometry allows a compound to be isolated from the rest of the sample and dissociated into smaller fragments. We show here that fragmentation of glutamate mass isotopomers yields additional mass spectral data that significantly improve the analysis of metabolic fluxes compared to full-scan mass spectrometry. In order to validate the technique, tandem and full-scan mass spectrometry were used along with (13)C NMR to analyze glutamate from rat hearts perfused with three substrate mixtures (5 mM glucose plus 5 mM [2-(13)C]acetate, 5 mM [1-(13)C]glucose plus 5 U/L insulin, and 5 mM glucose plus 1 mM [3-(13)C]pyruvate). Analysis by tandem mass spectrometry showed that the enriched substrate contributed 98 +/- 2, 53 +/- 2, and 84 +/- 7%, respectively, of acetyl-coenzyme A while the rate of anaplerotic substrate entry was 7 +/- 3, 25 +/- 8, and 16 +/- 8%. Similar results were obtained with (13)C NMR data, while values from full-scan data had higher error. We believe that this is the first use of tandem mass spectrometry to determine pathway flux using (13)C-enriched substrates. Although analysis of the citric acid cycle by NMR is simpler (and more intuitive), tandem mass spectrometry has the potential to combine high sensitivity with the high information yield previously available only by NMR.
authors.affiliation: The Mary Nell and Ralph B. Rogers Magnetic Resonance Center, Department of Radiology, University of Texas Southwestern Medical Center, Dallas 75390-9085, USA.
authors.forename: F Mark H
authors.initials: FM
authors.lastname: Jeffrey
authors.forename: J Shawn
authors.initials: JS
authors.lastname: Roach
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Storey
authors.forename: A Dean
authors.initials: AD
authors.lastname: Sherry
authors.forename: Craig R
authors.initials: CR
authors.lastname: Malloy
mesh_terms: D000818:Animals; D002247:Carbon Isotopes; D018698:Glutamic Acid / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D013058:Mass Spectrometry / Q000379:methods*; D008956:Models, Chemical; D009206:Myocardium / Q000737:chemistry*; D010477:Perfusion; D051381:Rats; D012680:Sensitivity and Specificity
chemical_list: D002247:Carbon Isotopes; D018698:Glutamic Acid