title: Chemical Assignment of Structural Isomers of Sulfur-Containing Metabolites in Garlic by Liquid Chromatography-Fourier Transform Ion Cyclotron Resonance-Mass Spectrometry.
abstract: BACKGROUND
  The chemical assignment of metabolites is crucial to understanding the relation between food composition and biological activity.
  
  
  OBJECTIVE
  This study was designed to detect and chemically assign sulfur-containing metabolites by using LC-Fourier transform ion cyclotron resonance-mass spectrometry (FTICR-MS) in Allium plants.
  
  
  METHODS
  Ultrahigh resolution (>250,000 full width at half-maximum) and mass accuracy (<1 mDa) by FTICR-MS allowed us to distinguish ions containing sulfur isotopes ((32)S and (34)S).
  
  
  RESULTS
  Putative 69 S-containing monoisotopic ions (S-ions) were extracted from the metabolome data of onion (Allium cepa), green onion (Allium fistulosum), and garlic (Allium sativum) on the basis of theoretical mass differences between (32)S-ions and their (34)S-substituted counterparts and on the natural abundance of (34)S. Eight S-ions were chemically assigned by using the reference data according to the guidelines of the Metabolomics Standards Initiative. Three ions detected in garlic were assigned as derived from the isomers γ-glutamyl-S-1-propenylcysteine and γ-glutamyl-S-2-propenylcysteine and as S-2-propenylmercaptoglutathione on the basis of differences in key product ions identified in reference tandem MS spectra.
  
  
  CONCLUSIONS
  The ability to discriminate between such geometric isomers will be extremely useful for the chemical assignment of unknown metabolites in MS-based metabolomics.
authors.affiliation: RIKEN Center for Sustainable Resource Science, Yokohama, Japan; ryo.nakabayashi@riken.jp kazuki.saito@riken.jp.
authors.forename: Ryo
authors.initials: R
authors.lastname: Nakabayashi
authors.affiliation: RIKEN Center for Sustainable Resource Science, Yokohama, Japan;
authors.forename: Yuji
authors.initials: Y
authors.lastname: Sawada
authors.affiliation: Central Research and Development Institute, House Foods Group, Inc., Chiba, Japan;
authors.forename: Morihiro
authors.initials: M
authors.lastname: Aoyagi
authors.affiliation: RIKEN Center for Sustainable Resource Science, Yokohama, Japan;
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Yamada
authors.affiliation: RIKEN Center for Sustainable Resource Science, Yokohama, Japan;
authors.forename: Masami Yokota
authors.initials: MY
authors.lastname: Hirai
authors.affiliation: RIKEN Center for Sustainable Resource Science, Yokohama, Japan;
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Sakurai
authors.affiliation: Central Research and Development Institute, House Foods Group, Inc., Chiba, Japan;
authors.forename: Takahiro
authors.initials: T
authors.lastname: Kamoi
authors.affiliation: The New Zealand Institute for Plant and Food Research, Palmerston North, New Zealand; and.
authors.forename: Daryl D
authors.initials: DD
authors.lastname: Rowan
authors.affiliation: RIKEN Center for Sustainable Resource Science, Yokohama, Japan; Graduate School of Pharmaceutical Sciences, Chiba University, Chiba, Japan ryo.nakabayashi@riken.jp kazuki.saito@riken.jp.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Saito
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods; D017357:Cyclotrons; D003545:Cysteine / Q000032:analysis*; D005737:Garlic / Q000737:chemistry*; D005978:Glutathione / Q000032:analysis*; D007477:Ions / Q000032:analysis*; D007536:Isomerism; D055442:Metabolome; D055432:Metabolomics; D019697:Onions / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*; D013455:Sulfur / Q000032:analysis*; D013460:Sulfur Isotopes / Q000032:analysis
chemical_list: D007477:Ions; D013460:Sulfur Isotopes; D013455:Sulfur; D005978:Glutathione; D003545:Cysteine
keywords: Allium cepa; Allium sativum; LC-FTICR-MS; S-containing metabolites; S-omics; chemical assignment