Characterization of water-insoluble proteins in normal and cataractous human lens

The mechanism of lens protein aggregation with age and/or cataract formation was investigated using the peptides resolubilized from the insoluble protein fraction of normal and cataractous human lenses. The insoluble fraction was treated with reductants for cleaving disulfide bonds, or with chelating agents for removing calcium ions from the aggregates. This study demonstrates that the insoluble protein aggregates consist of an approximately 400 Kd complex, which is formed by the peptides with lower molecular weight. Protein aggregation in the cataractous lens might be caused by disulfide bonds whereas, in aging, the aggregate might be preferentially formed by calcium ion bridges rather than by disulfide bonds. It was observed that the aggregate from the cataractous lenses involved a peptide with a molecular mass lower by 1 Kd or 2 Kd than the peptides found in the normal lens. The composition of crystallins in aggregating proteins and their secondary structures were also different in the normal and the cataractous lenses. Such changes of molecular weight, conformation, and/or crystallin species in the lens may lead to the disintegration of the orderly arrangement of crystallins, resulting in the diffused reflection and lens opacities which are seen in senile cataract.