L histidine monohydrochloride monohydrate

The assay buffer consisted of 10 mm 4‐(2‐hydroxyethyl)‐1‐piperazineethanesulfonic acid (HEPES), 130 mm NaCl, 10 mm glucose, 5 mm KCl, 2 mm CaCl₂, and 1.2 mm MgCl₂ (pH adjusted to 7.4 with NaOH). The ligands were diluted with the assay buffer at the desired concentrations.
Amino acids were obtained from commercial sources as follows. l‐cysteine, l‐aspartic acid sodium salt, l‐phenylalanine, glycine, l‐histidine monohydrochloride monohydrate, l‐lysine monohydrochloride, l‐proline (l‐Pro), l‐arginine (l‐Arg) hydrochloride, l‐serine, and l‐tyrosine were purchased from Nacalai Tesque (Kyoto, Japan); l‐alanine (l‐Ala), l‐isoleucine, l‐leucine, l‐asparagine monohydrate, l‐glutamine (l‐Gln), l‐threonine, l‐valine, and l‐tryptophane were purchased from Kanto Chemical (Tokyo, Japan); l‐glutamic acid monosodium salt was purchased from Sigma–Aldrich Japan (Tokyo, Japan); and l‐methionine was obtained from Tokyo Chemical Industry (Tokyo, Japan).

Samples were obtained from commercial sources as follows: l-aspartic acid sodium salt, l-glutamic acid monosodium salt, l-serine, l-lysine monohydrochloride, l-histidine monohydrochloride monohydrate, l-proline, and l-phenylalanine were purchased from Nacalai Tesque; l-glutamine, l-threonine, glycine, l-alanine, l-valine, l-isoleucine, l-leucine, l-arginine, and l-asparagine monohydrate were obtained from Kanto Chemical; l-methionine, methionol, pentanal, 3-(methylthio)propionic acid, and 3-(methylthio)butanal were obtained from Tokyo Chemical Industry; methional was from Sigma Aldrich; 2-methylthioacetaldehyde was from Penta Manufacturing Company; 3-(ethylthio)propanal was from Enamine Ltd.; 4-(methylthio)butanal was from FCH Group; and coelenterazine was purchased from Promega.