Diamide-induced cross-linking of the lens water-soluble proteins as a model of the early oxidative changes during senile cataract formation.

This study deals with the effects of the SH oxidizing agent diamide (diazene dicarboxylic acid bis-(N,N-dimethyl-amide)) on the water-soluble proteins from rabbit lenses. The dialyzed protein extracts were incubated for 0.5-1.5 h with various concentrations of diamide. Alterations in sulphydryl contents, gel filtration and gel electrophoresis profiles of proteins were recorded. The response to 2 mM diamide treatment for 1 h consists of rapid oxidation (up to 40%) of protein-bound sulphydryl groups accompanied by appearance of polypeptides with apparent molecular weights in excess of 68,000. A protein with a molecular weight of 29 kDa was shown to be specially involved in cross-linking. The linkages in the dialyzed water-soluble lens protein fraction induced by diamide may be reduced by GSH (10 mM) treatment of the protein extract. The main target of oxidative insult induced by diamide in the water-soluble proteins of the lens is probably the superficially localized sulphydryl groups of crystallins. Our observations suggest that this oxidative system of proteins may be a useful tool for cataract research.