Combined use of ¹H-NMR and GC-MS for metabolite monitoring and in vivo ¹H-NMR assignments

Thirty-three metabolites were observed in perchloric acid extracts of four different tissues by in vitro ¹H-NMR, GC-MS and alcohol dehydrogenase assay, and the information was used to interpret an in vivo two-dimensional nuclear Overhauser effect ¹H-NMR spectrum. The metabolite profiles of the differt tissues indicate a number of potential tissue-specific markers: N-acetylaspartate and γ-aminobutyric acid for rat brain, glutamine/glutamic acid ratio for dog heart, arginine and sucrose for carrot, and t-aconitate, sucrose, aspragine/aspartic acid concentration ratios for corm roots. γ-Aminobutyric acid and malate can be regarded as metabolic indicators for stressed corn roots. Concentrations of threonine and valine in corn roots were constant under hypoxic and salt stress, and can serve as internal standards for both in vivo and in vitro NMR studies. The in vitro information was further used to identify 12 compounds from the in vivo ¹H-NMR spectra (including the two-dimensional nuclear Overhauser effect spectrum) of a carrot cylinder by correlating the chemical shift and nuclear Overhauser effect information. Thus, our choice of methods with a capability for structural determination allows the characterization of complex tissue extracts with minimum sample preparation, and supports, as well as complements, in vivo ¹H-NMR investigations of metabolism.