title: Studies of the intermediary metabolism in cultured cells of the insect Spodoptera frugiperda using 13C- or 15N-labelled tracers.
abstract: BACKGROUND
  Insect cells can serve as host systems for the recombinant expression of eukaryotic proteins. Using this platform, the controlled expression of 15N/13C labelled proteins requires the analysis of incorporation paths and rates of isotope-labelled precursors present in the medium into amino acids. For this purpose, Spodoptera frugiperda cells were grown in a complex medium containing [U-13C6]glucose. In a second experiment, cultures of S. frugiperda were grown in the presence of 15N-phenylalanine.
  
  
  RESULTS
  Quantitative NMR analysis showed incorporation of the proffered [U-13C6]glucose into the ribose moiety of ribonucleosides (40 - 45%) and into the amino acids, alanine (41%), glutamic acid/glutamine (C-4 and C-5, 30%) and aspartate/asparagine (15%). Other amino acids and the purine ring of nucleosides were not formed from exogenous glucose in significant amounts (> 5%). Prior to the incorporation into protein the proffered 15N-phenylalanine lost about 70% of its label by transamination and the labelled compound was not converted into tyrosine to a significant extent.
  
  
  CONCLUSIONS
  Growth of S. frugiperda cells in the presence of [U-13C6]glucose is conducive to the fractional labelling of ribonucleosides, alanine, glutamic acid/glutamine and aspartic acid/asparagine. The isotopolog compositions of the ribonucleosides and of alanine indicate considerable recycling of carbohydrate intermediates in the reductive branch of the pentose phosphate pathway. The incorporation of 15N-labelled amino acids may be hampered by loss of the 15N-label by transamination.
authors.affiliation: Lehrstuhl für Organische Chemie und Biochemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany. petra.adam@gx.novartis.com
authors.forename: Petra
authors.initials: P
authors.lastname: Adam
authors.forename: Markus
authors.initials: M
authors.lastname: Gütlich
authors.forename: Hartmut
authors.initials: H
authors.lastname: Oschkinat
authors.forename: Adelbert
authors.initials: A
authors.lastname: Bacher
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Eisenreich
mesh_terms: D000818:Animals; D002247:Carbon Isotopes / Q000378:metabolism; D002478:Cells, Cultured; D009587:Nitrogen Isotopes / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D018411:Spodoptera / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes