Redox cycling in iron uptake, efflux, and trafficking

Aerobic organisms are faced with a dilemma. Environmental iron is found primarily in the relatively inert Fe(III) form, whereas the more metabolically active ferrous form is a strong pro-oxidant. This conundrum is solved by the redox cycling of iron between Fe(III) and Fe(II) at every step in the iron metabolic pathway. As a transition metal ion, iron can be " metabolized" only by this redox cycling, which is catalyzed in aerobes by the coupled activities of ferric iron reductases (ferrireductases) and ferrous iron oxidases (ferroxidases).