Radiation-induced changes in flavin fluorescence of dihydroorotate dehydrogenase

The effect of γ-radiation on the flavin moiety of dihydroorotate dehydrogenase was studied by fluorescence spectroscopy. Irradiation of aerated solutions (0-7Gy) led to a small increase in fluorescence intensity, but with higher doses a decrease in intensity was observed. The increase in fluorescence intensity after irradiation at low doses may be attributed to protein unfolding, leading to greater exposure of flavin groups and a concomitant increase in separation between the flavin moiety and the iron-sulphur centre, confirmed by fluorescence quenching studies using potassium iodide as quencher. No spectral change was observed when unirradiated or irradiated enzyme was denatured with guanidine hydrochloride. However, a decrease in fluorescence intensity in the case of irradiated samples indicated a radiation-induced decrease in the flavin fluorophore. (author)