Free Flavin Participates in Iron and Also Oxygen Metabolism in Bacteria

The reduction of ferric iron to ferrous iron is an essential reaction for the utilization of iron in vivo and ferric reductase participate in this reduction. There are two types of ferric reductase reactions: a reaction using free flavin (non-protein-bound flavin), and a reaction independent of free flavin. However, most of all ferric reductase activities tested to date, including both types of ferric reductases, are enhanced by the addition of free flavin. In E. coli, the iron release from iron storage proteins is markedly stimulated by both types of ferric reductases in the presence of free flavin. Free flavins can directly carry electrons toward molecular oxygen in the aerobic metabolism of an aerotolerant anaerobe, Ampibacillus xylanus. The free flavin and its associated system are able to participate in oxygen and iron metabolism during aerobic bacterial growth. The reaction products of reduced free flavin with oxygen and Fe3+ cause the Fenton reaction, producing the most cytotoxic hydroxyl radical, •OH. Finally, the contribution of free flavin to the process of the Fenton reaction is discussed here.