L lysine monohydrochloride

Agar (purified powder) was obtained from Sigma-Aldrich (St Louis, MO, USA). As tastants, D-fructose (CAS: 57-48-7, Wako Pure Chemical Industries, Ltd., Osaka, Japan), as well as L-alanine (ALA; CAS: 56-41-7), L-arginine monohydrochloride (ARG; CAS: 1119-34-2), L-asparagine monohydrate (ASN; CAS: 5794-13-8), L-aspartic acid (ASP; CAS: 56-84-8), L-cysteine monohydrochloride hydrate (CYS; CAS: 7048-04-6), L-histidine monohydrochloride (HIS; CAS: 645-35-2), L-isoleucine (ILE; CAS: 73-32-5), L-leucine (LEU; CAS: 61-90-5), L-lysine monohydrochloride (LYS; CAS: 657-27-2), L-glutamine (GLN; CAS: 56-85-9), L-glutamic acid (GLU; CAS: 56-86-0), L-glycine (GLY; CAS: 56-40-6), L-methionine (MET; CAS: 63-68-3), L-phenylalanine (PHE; CAS: 63-91-2), L-proline (PRO; CAS: 147-85-3), L-serine (SER; CAS: 56-45-1), L-threonine (THR; CAS: 72-19-5), L-tryptophan (TRP; CAS: 73-22-3), L-tyrosine (TYR; CAS: 60-18-4) and L-valine (VAL; CAS: 72-18-4) were used at concentrations of 10 mmol l⁻¹ (TYR was used in 0.5 mmol l⁻¹ due to low solubility). Amino acids were obtained from Wako Pure Chemical Industries, Ltd., Osaka, Japan (TYR, SER, CYS, VAL), Sigma-Aldrich, St Louis, MO, USA (ILE, PRO) or Nacalai Tesque, Kyoto, Japan (ALA, ARG, ASN, ASP, LEU, LYS, GLN, GLY, MET, PHE, THR, TRP, TYR).

All chemical and chromatographic reagents used were of HPLC or LC/MS grade. Pyridoxamine dihydrochloride monohydrate was obtained from Tokyo Chemical Industry (Tokyo, Japan). D(+)-Xylose, L(+)-lysine monohydrochloride, acetonitrile (ACN), and 1 M ammonium formate solution were obtained from Wako Pure Chemical Industry (Osaka, Japan). D-[1-¹³C]xylose (99%) was obtained from Cambridge Isotope Laboratories, Inc. (MA, USA). Other reagents were obtained from Kanto Kagaku (Tokyo, Japan).