Iron and Its Catalytic Properties on Radical Generation: Role of chelators on the labile iron pool (LIP)

Abstract

Iron (Fe) is an essential element for the growth and well-being of almost all living organisms as it is involved in many biological functions since by varying the ligands to which it is coordinated. Fe has access to a wide range of redox potentials and can participate in many electron transfer reactions, spanning the standard redox potential range. It is also involved in O2 transport, activation, and detoxification, in N2 fixation and in several of the reactions of photosynthesis. However, there are problems in the physiological management of Fe. Anytime Fe exceeds the metabolic needs of the cell it may form low molecular weight pool, referred as the labile iron pool (LIP), which catalyzed the conversion of normal by-products of cell respiration, like superoxide anion (O2-) and hydrogen peroxide (H2O2), into highly damaging hydroxyl radical (?OH) through the Fenton reaction or by the Fe2+-catalyzed Haber-Weiss reaction, or into equally aggressive ferryl ions or O2-bridged Fe2+/Fe3+ complexes. Fe3+ can be reduced either by O2- or by ascorbate (AH-) leading to further radical production. The LIP consists of Fe2+ and Fe3+ associated with a variety of ligands with low affinity for Fe ions. However, the intracellular ligands participating in LIP formation remains obscure and the accessibility of cellular Fe to chelators is commonly used as the criterion of ´lability´. This chapter was intended to summarize the current knowledge on the nature and the function of LIP in cellular oxidative conditions.