THE NAD(P)H-FLAVIN OXIDOREDUCTASE FROM ESCHERICHIA-COLI AS A SOURCE OF SUPEROXIDE RADICALS

The NAD(P)H:flavin oxidoreductase (encoded by the fre gene) of Escheri chia coil is a soluble enzyme which, under aerobic conditions and toge ther with NAD(P)H and flavins, generates superoxide radicals selective ly. This was demonstrated from spin trapping experiments and from the ability of the flavin reductase to achieve a superoxide dismutase (SOD )-sensitive reduction of cyto chrome c. The participation of the flavi n reductase to O-2(radical-anion). generation in E. coli cells has bee n studied. Superoxide production in dialyzed cytosolic fraction of SOD -deficient E. coli was stimulated by the addition of flavins. There wa s no stimulation in soluble extracts of flavin reductase-deficient str ains. Moreover, using fusions of sodA promoter to lacZ, we showed that sodA transcription was diminished in flavin reductase-deficient E. co il and that the induction of MnSOD by flavin reductase was SoxRS-indep endent. These results suggest that the flavin reductase might: (i) in vivo, be an important cytosolic site of O-2(radical-anion). generation ; (ii) in vitro, serve as a simple, efficient, and selective O-2(radic al-anion). generator.