Ferrous ion release from ferritin by ultraviolet-A radiations

Ferritin is the principal protein of iron storage (in the Fe(III) state). The UV-A irradiation of 0.25 μM ferritin solutions (from horse spleen) loaded with 530 μM Fe(III) induces Fe2+ release in the medium. The initial quantum yield is wavelength dependent (φ(365 nm) ∼2 x 10-3) but pH and oxygen independent. The Fe2+ release reaches a plateau which strongly depends on pH and oxygen. The amino acid composition of the apoprotein is not altered by the UV irradiation. Addition of formate ions enhances the Fe2+ production, suggesting that the ferritin photoreduction involves an electron transfer from an OH- ligand. The possible importance of this phenomenon in skin photobiology is discussed. (author)