Lens proteins and aging.

Aging of the eye lens is reflected by pronounced changes on the molecular level. So far, these alterations have been investigated in particular with respect to the structural lens proteins or crystallins, which comprise approximately 95% of the dry weight. It seems that virtually postsynthetic modifications are involved, although errors on the translational level cannot be excluded. A variety of chemically or physically defined processes have been observed with aging. These include formation of high-molecular-weight, eventually insoluble aggregates; formation of disulfide bridges and other covalent crosslinks; deamidation of asparaginyl and glutaminyl residues; partial degradation of polypeptides at characteristic sites; racemization of aspartyl residues; nonenzymatic glycosylation; and photooxidation of tryptophanyl residues.