L valine

C57bl6/j mice were obtained from Jackson Laboratories (Stock #000664). Labeled internal standards citric acid (2,2,4,4-D4, 98%; #DLM-3487), succinic acid (2,2,3,3-D4, 98%; #DLM-584), l-valine (2,3,4,4,4,5,5,5-D8; 98%; #DLM-311), l-glutamic acid (¹³C5, 99%; #CLM-1800), l-glutamine (¹³C5, 99%, #CLM-1822), l-lysine (¹³C6, 99%; #CLM-2247), l-methionine (¹³C5, 99%; #CLM-893), and l-tryptophan (¹³C11, 99%; #CLM-4290) and tracer glucose (¹³C6, 99%, #CLM-1396) were obtained from Cambridge Isotope Laboratories, Inc. AAV8-TBG-NULL (#105536-AAV8) and AAV8-TBG-Cre (#107787-AAV8) were purchased from Addgene. Pre-filled bead mill tubes containing 1.4 mm ceramic beads (#15-340-153) were purchased from FisherScientific. Methoxaymine hydrochloride (#226904, MOX) and N-methyl-N-(trimethylsilyl) trifluoroacetamide (#694709, MSTFA) were purchased from Sigma Aldrich. Protease inhibitor cocktail (#786-437) was purchased from G Biosciences. Bio-Rad protein assay dye regent (#5000006) and 0.45 μm nitrocellulose membrane (#1620115) were purchased from Bio-Rad.

The purity assessed CRMs of
the target AAs (l-Proline, l-Valine, l-Isoleucine, l-leucine, l-phenylalanine, and l-tyrosine)
were obtained from the National Metrology Institute of Japan (NMIJ,
Japan). The following isotopic labeled Aas for the ISTDs were obtained
from Cambridge Isotopes Laboratory (Andover, MA): l-Proline
(U-¹³C₅, 99%; ¹⁵N, 99%; Pro*), l-Valine (U-¹³C₅, 97–99%;¹⁵N,97–99%; Val*), l-Isoleucine (U-¹³C₆, 99%; ¹⁵N, 99%; Ile*), l-Leucine (U-¹³C₆, 97–98%; ¹⁵N, 97–98%;
Leu*), l-Phenylalanine (U-¹³C₉, 99%; ¹⁵N, 99%; Phe*), and l-Tyrosine (¹³C₉, 99%; Tyr*). All other chemicals used in this study are summarized
in the Supporting Information.

PC(12:0/13:0), PE(12:0/13:0), SM(d18:1/12:0) and Cer(d18:1/12:0) were purchased from Avanti Polar Lipids (Alabaster, AL, USA). Stable isotope labeled references were purchased from Cambridge Isotope Laboratories (Andover, MA, USA), including: Glycine (2-¹³C, ¹⁵N), L-Alanine (2,3,3,3-D₄), L-Valine (D₈), L-Leucine (5,5,5-D₃), L-Methionine (methyl-D₃), L-Phenylalanine (ring-¹³C₆), L-Tyrosine (ring-¹³C₆), L-Aspartic acid (2,3,3-D₃), DL-Glutamic acid (2,4,4-D₃), L-Ornithine: HCl (5,5-D₂), L-Citrulline (5,5-D₂) and L-Arginine (5-¹³C, 4,4,5,5-D₄). Deuterium-labeled carnitine and acylcarnitines (NSK-B set) were purchased from Cambridge Isotope Laboratories (Tewksbury, MA, USA), including ²H₃-Acetylcarnitine (C₂), ²H₃-Propionylcarnitine (C₃), ²H₃-Butyrylcarnitine (C₄), ²H₉-Isovalerylcarnitine (C₅), ²H₃-Octanoylcarnitine (C₈), ²H₉-Myristoylcarnitine (C₁₄), and ²H₃-Palmitoylcarnitine (C₁₆). HPLC-grade ammonium acetate was purchased from Sigma-Aldrich (St. Louis, MO, USA), and HPLC-grade formic acid and acetonitrile were purchased from Thermo Fisher Scientific (Waltham, MA, USA). All solutions were prepared by LC-MS ultra-pure water.