In vitro evidence for a relationship between magnesium and vitamin B-6

Vitamin B-6 and magnesium appear to interact in vivo and it has been suggested that vitamin B-6 may enhance transport or accumulation of magnesium in cells. The purpose of this study was to evaluate the possibility of the formation of B-6 vitamer-Mg complexes in vitro using spectrophotometric analysis of ultraviolet or visible spectra or change in fluorescence intensity of B-6 vitamers. Pyridoxal phosphate but not pyridoxal appears to form a complex with Mg as evidenced by a change in the ultraviolet and visible spectra with an increase in absorption and spectral shift in the visible maxima from 389 to 388 nm and a decrease in the ultraviolet absorption maxima at 296 nm. Addition of Mg to pyridoxal phosphate but not the other B-6 vitamers enhanced the fluorescent intensity of pyridoxal phosphate at least threefold and evoked a spectral shift in both the fluorescence excitation and emission maximum. Electrochemical titration of pyridoxal phosphate in the presence of Mg affects the pKa- of the phenolic hydroxyl and the secondary phosphate ionization. These data collectively indicate that pyridoxal phosphate, but not pyridoxal, appears to form a coordinated complex with Mg and the coordination site is likely to be related to the primary phosphate and aldehyde moiety of pyridoxal phosphate.