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Photo‐Induced Processes in Vitamin B 6 Compounds
Author(s) -
Vilanova Bartolomé,
Adrover Miquel,
Muñoz Francisco,
Donoso Josefa
Publication year - 2004
Publication title -
chemistry and biodiversity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.427
H-Index - 70
eISSN - 1612-1880
pISSN - 1612-1872
DOI - 10.1002/cbdv.200490080
Subject(s) - chemistry , tautomer , pyridoxamine , pyridoxal , schiff base , pyridoxal phosphate , irradiation , absorption spectroscopy , vitamin b6 , photochemistry , phosphate , stereochemistry , vitamin , organic chemistry , enzyme , biochemistry , physics , cofactor , quantum mechanics , nuclear physics
In this work, we applied multi‐wavelength stopped‐flow spectroscopy (MSFS) to study the chemical equilibria between tautomeric or hydrated forms of various vitamin B 6 compounds and the Schiff base formed by ε ‐aminocaproic acid (=6‐aminohexanoic acid) with pyridoxal 5′‐phosphate at 25° 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 ε ‐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 B 6 ‐dependent enzymes by the MSFS technique, whenever some free vitamer may be present in solution.