81] Dithionite-induced changes in the spectra of free and enzyme-bound pyridoxal phosphate

Abstract

Publisher Summary This chapter describes the dithionite-induced changes in the spectra of free and enzyme-bound pyridoxal phosphate. Treatment of free pyridoxal phosphate at neutral pH with excess dithionite produces a rapid change in the pyridoxal phosphate spectrum. The special change with dithionite is slow at lower dithionite concentrations. Two considerations make the dithionite reaction of enzymologic interest. The spectral change might be distinctive enough to identify a pyridoxal phosphate enzyme. Additionally, the spectral shift of enzyme bound pyridoxal phosphate on dithionite treatment should be kept in mind in interpreting presumptive flavin difference spectra. While the existence of single enzymes containing both a flavin and pyridoxal phosphate coenzyme has not been reliably documented, enzyme mixtures, or multienzyme aggregates of physiological significance, might create an occasion for this confusion. Alanine racemase is of special interest in connection with a dithionite difference spectrum because the enzyme contains a flavin prosthetic group together with pyridoxal phosphate.