title: The 15N isotope effect in Escherichia coli: a neutron can make the difference.
abstract: Several techniques based on stable isotope labeling are used for quantitative MS. These include stable isotope metabolic labeling methods for cells in culture as well as live organisms with the assumption that the stable isotope has no effect on the proteome. Here, we investigate the (15) N isotope effect on Escherichia coli cultures that were grown in either unlabeled ((14) N) or (15) N-labeled media by LC-ESI-MS/MS-based relative protein quantification. Consistent protein expression level differences and altered growth rates were observed between (14) N and (15) N-labeled cultures. Furthermore, targeted metabolite analyses revealed altered metabolite levels between (14) N and (15) N-labeled bacteria. Our data demonstrate for the first time that the introduction of the (15) N isotope affects protein and metabolite levels in E. coli and underline the importance of implementing controls for unbiased protein quantification using stable isotope labeling techniques.
authors.affiliation: Max Planck Institute of Psychiatry, Proteomics and Biomarkers, Munich, Germany.
authors.forename: Michaela D
authors.initials: MD
authors.lastname: Filiou
authors.forename: Jeeva
authors.initials: J
authors.lastname: Varadarajulu
authors.forename: Larysa
authors.initials: L
authors.lastname: Teplytska
authors.forename: Stefan
authors.initials: S
authors.lastname: Reckow
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Maccarrone
authors.forename: Christoph W
authors.initials: CW
authors.lastname: Turck
mesh_terms: D002853:Chromatography, Liquid; D004926:Escherichia coli / Q000378:metabolism*; D007553:Isotope Labeling / Q000379:methods*; D009502:Neutrons; D009587:Nitrogen Isotopes / Q000737:chemistry*; D020543:Proteome / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D040901:Proteomics / Q000379:methods*; D053719:Tandem Mass Spectrometry
chemical_list: D009587:Nitrogen Isotopes; D020543:Proteome