Oxidative modification of lens crystallins by H 2O 2 and chelated iron

Abstract

Crystallins are the soluble structural proteins that constitute approximately 90% of the dry mass of the eye lens. The present study attempts to elucidate possible mechanisms whereby the H 2O 2 present in the eye could contribute to the oxidative modification of lens crystallins. The data indicate that exposure of solutions of crystallins to H 2O 2 and EDTA-chelated iron leads to covalent crosslinking of polypeptides, loss of intrinsic protein fluorescence, and the generation of a novel flurophor emitting in the 420 nm range. These changes closely mimic oxidative modifications that occur in lens proteins in vivo. Exposure of the proteins to H 2O 2 in the absence of chelated iron failed to generate detectable levels of these modifications. These findings are contrasted with earlier studies of lenses in organ culture where H 2O 2 alone produced marked damage while the further addition of chelated iron protected the lenses from oxidation.