Spermine d20

S-adenosylmethionine-¹³C₅ (#A291533), N1-acetylspermidine (#A187845), Putrescine-d8 (#D416027), spermidine-d6 (#S680407), spermine-d20 (#S680512) were purchased from Toronto Research Chemicals (Toronto, Ontario, Canada). S-Adenosylhomocysteine-d4 (#13603), spermidine (#14918) and spermine (#18041) were purchased from Cayman Chemical (Ann Arbor, MI). Putrescine (D13208), homocysteic acid (#44925), N,N-dimethylglycine (#05022), amino acid standards solution (A9906), and the cell free amino acid mixture-¹³C,¹⁵ N (#767964) were purchased from Sigma-Aldrich. Standard calibration curves between 0.01 and 10 µM were constructed using serially diluted unlabeled standards with internal standards at 2 µM.

Acetonitrile (LC-MS grade) was purchased from Merck (Darmstadt, Germany), and methanol and formic acid (both LC-MS grade) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Chloroform, sodium bicarbonate, sodium carbonate, ammonium acetate, trifluoroacetic acid, perchloric acid, sodium hydroxide, acetone, and dansyl chloride were obtained from Sigma-Aldrich, whereas ethyl acetate was obtained from Merck. The water used throughout the study was purified in a Milli-Q system from Millipore (Burlington, MA, USA).
N1-acetylspermidine (N1-AcSPD), N8-acetylspermidine (N8-AcSPD), spermine-d20, spermine, spermidine-d6, spermidine, putrescine-d8, putrescine, N1,N12-diacetylspermine, N1,N8-diacetylspermidine (N1,N8-DiAcSPD), N8-acetylspermidine-d3, N1,N8-diacetylspermidine (N1,N8-DiAcSPD-d6), and agmatine were acquired from Toronto Research Chemicals (North York, ON, Canada). Cadaverine, N-acetylputrescine, N-acetylspermine (N1-AcSPM), lysine, ornithine, arginine, γ-aminobutyric acid, and 1,3-diaminopropane were purchased from Sigma-Aldrich. Lysine (¹³C₆,¹⁵N₂) and arginine (¹³C₆,¹⁵N₄) were supplied by Cambridge Isotope Laboratories (Tewksbury, MA, USA).
Oasis HLB cartridges (1 cc Vac Cartridge, 30 mg sorbent, and 30 µm particle size) were acquired from Waters (Milford, MA, USA).