Electron spin resonance characterization of the radicals produced by enzymatic or chemical cleavage of vicine

Vicine is a glucoside from broad beans (Vicia faba) that is hydrolyzed upon ingestion to the unstable aglycon divicine, the autoxidation of which has been implicated in the onset of hemolysis in favism,possibly via production of superoxide and hydrogen peroxide. The autoxidation of divicine proceeds through a series of reactions involving the formation of a radical species. In this study divicine radicals were produced either by incubation of vicine with beta-glucosidase or by boiling vicine in hydrochloric acid. On the basis of electron spin resonance spectra, it was shown that the two treatments produce different radicals. By spectral simulation the acid-produced radical was demonstrated to be a deaminodivicine. The autoxidation rates of the two radicals were determined from the disappearence of their electron spin resonance signals in the presence of air: at physiological pH the enzymatically produced divicine radical was much more stable to oxygen than the chemically produced radical. The two radicals may thus be expected to behave differently in a biological system. The repercussions of these findings could be considerable, given that most of the pharmacological and biochemical studies on vicine action have been done with the chemically produced compound, which is shown here to be an unphysiological intermediate.