Reaction of dithionite and bisulfite with pyridoxal and pyridoxal enzymes

Abstract

Both bisulfite and dithionite produce marked changes in the spectra of pyridoxal, pyridoxal phosphate, and pyridoxal phosphate enzymes. The spectrum of pyridoxal phosphate in bisulfite solutions resembles that of the addition product of pyridoxal phosphate with cysteine. The spectral changes produced by dithionite are distinctly different from those produced by bisulfite and, unlike the latter, are not prevented by acetone. As judged by spectral change, pyridoxal phosphate enzymes appear less reactive with bisulfite than with dithionite, relative to the reactivity of the free coenzyme. The nature of the dithionite reaction and of its products has not been determined. However, the difference spectrum attributable to dithionite reaction with enzyme-bound pyridoxal phosphate, while distinguishable from that of a flavin difference spectrum must be kept in mind in interpreting presumptive flavin difference spectra. In addition, dithionite may be a useful reagent for delineating, by difference spectra, the characteristic low 400 mμ peak of pyridoxal phosphate enzymes.