title: Photo-induced processes in vitamin B6 compounds.
abstract: In this work, we applied multi-wavelength stopped-flow spectroscopy (MSFS) to study the chemical equilibria between tautomeric or hydrated forms of various vitamin B6 compounds and the Schiff base formed by epsilon-aminocaproic acid (= 6-aminohexanoic acid) with pyridoxal 5'-phosphate at 25 degrees and variable pH. Since some of these compounds are photosensitive, we analyzed the possible occurrence of any secondary photo-induced processes under the conditions of irradiation in the MSFS equipment (continuous irradiation with light from a 75-W Xe lamp spanning the wavelength range of 200-700 nm). To determine the tautomeric composition of these compounds, the electronic absorption spectra were analyzed by means of log-normal curves. Continuous irradiation of pyridoxamine and pyridoxal 5'-phosphate over the wavelength range of 200-700 nm displaces the chemical equilibrium between the tautomeric or hydrated forms of these compounds. However, the Schiff base of epsilon-aminocaproic acid with pyridoxal 5'-phosphate is insensitive to the radiation used. The photo-induced processes detected in pyridoxamine and pyridoxal 5'-phosphate should be taken into account in examining vitamers by MSFS. In fact, these additional processes should be considered in studying the mechanism of action of vitamin B6-dependent enzymes by the MSFS technique, whenever some free vitamer may be present in solution.
authors.affiliation: Institut Universitari d'Investigació en Ciències de la Salut, Departament de Química, Universitat de les Illes Balears, E-07122 Palma de Mallorca.
authors.forename: Bartolomé
authors.initials: B
authors.lastname: Vilanova
authors.forename: Miquel
authors.initials: M
authors.lastname: Adrover
authors.forename: Francisco
authors.initials: F
authors.lastname: Muñoz
authors.forename: Josefa
authors.initials: J
authors.lastname: Donoso
mesh_terms: D008027:Light; D010777:Photochemistry / Q000379:methods*; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D014466:Ultraviolet Rays; D025101:Vitamin B 6 / Q000032:analysis / Q000737:chemistry* / Q000528:radiation effects*
chemical_list: D025101:Vitamin B 6