Reduction of low molecular mass iron by reducing molecules present in plasma and the protective action of caeruloplasmin.

Normal human plasma does not contain low molecular mass iron because the iron-binding protein transferrin retains a considerable iron-binding capacity. In conditions of iron-overload, however, low molecular mass iron can be detected in plasma. Plasma contains several molecules capable of reducing ferric complexes to the ferrous state and this could lead to oxidative damage through reactions dependent on Fenton chemistry and lipid peroxidation. It seems likely that ascorbate and urate would reduce ferric complexes present in plasma during iron-overload. However, the plasma, 'ferroxidase' protein caeruloplasmin protects the extracellular environment by catalytically oxidising ferrous complexes back to the less reactive ferric state.