2 oxoglutaric acid

ThDP, NAD⁺, CoA, DTT, isopropyl 1-thio-β-D-galactopyranoside, imidazole, thiamin-HCl, glycerol, DNase I, and Micrococcal nuclease were from Affymetrix (Thermo Fisher Scientific, Waltham, MA, USA); 2-oxoglutaric acid, 2-oxoadipic acid, iodoacetamide, benzamidine HCl, disuccinimidyl dibutyric urea (DSBU or BuUrBu), 1.1′-carbonyl-diimidazole (CDI), and dimethyl sulfoxide were from Sigma-Aldrich (St. Louis, MO, USA). Formic acid solution was obtained from Fluka Analytical (Buchs, Switzerland); MS grade trypsin protease was from Pierce; Ni Sepharose^® high-performance affinity media was from GE Healthcare (Chicago, IL, USA).

L-asparagine (≥98%), choline chloride (≥99%), creatine (≥99.5%), creatinine (≥98%), L-leucine (≥98%), L-methionine (≥98%), L-proline (≥99.5%), taurine (≥99%), L-valine (≥98%), 2-hydroxybutanoic acid, L-lactic acid (≥98%), malic acid (≥99%), and 2-oxo-glutaric acid (≥99%) were purchased from Sigma Aldrich (St. Louis, MO, United States). L-lactic acid-d₃ and choline-d₉ were obtained from Toronto Research Chemicals (Toronto, ON, Canada). L-asparagine ¹³C₄ (≥99%) and L-leucine-d₃ (≥99%) were obtained from Euriso-top (Saint-Aubin, France). Acetonitrile, formic acid, trifluoroacetic acid, isopropanol, methanol, and water (MS-grade) were bought from Biosolve (Valkenswaard, The Netherlands). hemaPEN^® devices were obtained from Trajan Scientific and Medical (VIC, Australia) and Ostro^® 96-well sample preparation plates from Waters Corporation (Dublin, Ireland). MiniCollect^® safety lancets were purchased from Greiner Bio-One (Vilvoorde, Belgium).