title: Characterization of enzymes involved in the interconversions of different forms of vitamin B(6) in tobacco leaves.
abstract: There are six different vitamin B(6) (VB(6)) forms, pyridoxal (PL), pyridoxamine (PM), pyridoxine (PN), pyridoxal 5'-phosphate (PLP), pyridoxamine 5'-phosphate (PMP) and pyridoxine 5'-phosphate (PNP). PLP is a coenzyme required by more than 100 cellular enzymes. In spite of the importance of this vitamin, the understanding of VB(6) metabolic conversion in plants is limited. In this study, we developed a sensitive and reliable method to assay VB(6)-metabolizing enzyme activities by monitoring their products visually using high-performance liquid chromatography. With this method, the reactions catalyzed by PL/PM/PN kinase, PMP/PNP oxidase, PM-pyruvate aminotransferase, PL reductase and PLP phosphatase were all nicely detected using crude protein extracts of tobacco leaves. Under optimal in vitro conditions, specific activities of those enzymes were 0.15 ± 0.03, 0.10 ± 0.03, 0.08 ± 0.02, 0.64 ± 0.13 and 23.08 ± 1.98 nmol product/min/mg protein, respectively. This is the first report on the conversion between PM and PL catalyzed by PM-pyruvate aminotransferase in plants. Furthermore, the PL reductase activity was found to be heat inducible. Our study sheds light on the VB(6) metabolism taking place in plants.
authors: Key Laboratory of Tea Biochemistry & Biotechnology of Ministry of Education and Ministry of Agriculture, Anhui Agricultural University, Hefei 230036, People's Republic of China.
authors: ShuoHao
authors: S
authors: Huang
authors: HaiBin
authors: H
authors: Zeng
authors: JianYun
authors: J
authors: Zhang
authors: Shu
authors: S
authors: Wei
authors: LongQuan
authors: L
authors: Huang
mesh_terms: D000429:Alcohol Oxidoreductases / Q000378:metabolism; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003067:Coenzymes; D004789:Enzyme Activation; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D053858:Metabolic Networks and Pathways; D010936:Plant Extracts / Q000378:metabolism*; D018515:Plant Leaves / Q000737:chemistry / Q000201:enzymology / Q000378:metabolism; D011732:Pyridoxal Phosphate / Q000378:metabolism; D014026:Nicotiana / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D000637:Transaminases / Q000378:metabolism; D025101:Vitamin B 6 / Q000378:metabolism*
chemical_list: D003067:Coenzymes; D010936:Plant Extracts; D011732:Pyridoxal Phosphate; D025101:Vitamin B 6; D000429:Alcohol Oxidoreductases; C022495:pyridoxine 4-dehydrogenase; D000637:Transaminases; C022494:pyridoxamine-pyruvate transaminase