Residual EDTA bound by lens crystallins accounts for their reported resistance to copper-catalyzed oxidative damage

It was recently reported that the structural proteins of the lens, the crystallins, possess unusual resistance to oxidative damage from a copper-catalyzed Fenton system. Data presented here demonstrate that this phenomenon is specific to copper-catalyzed systems and is not observed when iron is the metal catalyst. Further investigation has revealed that the apparent resistance to copper-catalyzed oxidation results from the presence of residual EDTA associated with the proteins. EDTA chelates the copper, inactivating it as a redox catalyst. This binding of EDTA to crystallins (or other proteins) occurs when the proteins present in EDTA-containing buffers are dialyzed directly against deionized water. Partial characterization of the association between EDTA and proteins is presented and its potential significance as a confounding factor in studies of the effects of metal-catalyzed oxidation on proteins is discussed.