ABSTRACT
A determination method for individual natural vitamin B(6) compounds was developed. The vitamin B(6) compounds were specifically converted into 4-pyridoxolactone (PAL), a highly fluorescent compound, through a combination of enzymatic reactions and HCl-hydrolysis. PAL was then determined by HPLC. Pyridoxal was completely oxidized to PAL with pyridoxal 4-dehydrogenase (PLDH). Pyridoxine and pyridoxamine were totally converted into PAL through a coupling reaction involving pyridoxine 4-oxidase and PLDH, and one involving pyridoxamine-pyruvate aminotransferase and PLDH, respectively. The 5'-phosphate forms and pyridoxine-beta-glucoside were hydrolyzed with HCl, and then determined as their free forms. Pyridoxine 5'-phosphate and pyridoxine-beta-glucoside were not separately determined here. Three food samples were analyzed by this method.
Subject(s)
Alcohol Oxidoreductases/chemistry , Food Analysis/methods , Pyridoxic Acid/analogs & derivatives , Transaminases/chemistry , Vitamin B Complex/analysis , Animals , Capsicum , Chickens , Chromatography, High Pressure Liquid/methods , Garlic , Glucosides/analysis , Glucosides/chemistry , Hydrochloric Acid/chemistry , Hydrolysis , Pyridoxic Acid/analysis , Pyridoxic Acid/chemical synthesis , Pyridoxine/analogs & derivatives , Pyridoxine/analysis , Pyridoxine/chemistry , Time Factors , Vitamin B 6/analysis , Vitamin B 6/chemistry , Vitamin B Complex/chemistryABSTRACT
Histamine, a biogenic amine with important biological functions, is produced from histidine by histidine decarboxylase (HDC), a pyridoxal 5'-phosphate-dependent enzyme. HDC is thus a potential target to attenuate histamine production in certain pathological states. Targeting mammalian HDC with novel inhibitors and elucidating the structural basis of their specificity for HDC are challenging tasks, because the three-dimensional structure of mammalian HDC is still unknown. In the present study, we designed, synthesized, and tested potentially membrane-permeable pyridoxyl-substrate conjugates as inhibitors for human (h) HDC and modeled an active site of hHDC, which is compatible with the experimental data. The most potent inhibitory compound among nine tested structural variants was the pyridoxyl-histidine methyl ester conjugate (PHME), indicating that the binding site of hHDC does not tolerate groups other than the imidazole side chain of histidine. PHME inhibited 60% of the fraction of 12-O-tetradecanoylphorbol-13-acetate-induced newly synthesized HDC in human HMC-1 cells at 200 microM and was also inhibitory in cell extracts. The proposed model of hHDC, containing phosphopyridoxyl-histidine in the active site, revealed the binding specificity of HDC toward its substrate and the structure-activity relationship of the designed and investigated compounds.
