Effect of opacification and pigmentation on human lens protein thiol/disulfide and solubility

In this study, we compared the thiol/disulfide status and the protein profiles for a group of normal lenses (over 60 years old) and a group of age matched cataractous lenses. In agreement with previous reports we found that the severity of the lens opacity and the color of the nucleus correlated well with the decrease of soluble proteins and increase of guanidine insoluble proteins. However, the decrease of nonprotein thiols and protein thiols was associated only with the pigmentation of the lenses. We discovered that protein-thiol mixed disulfide profiles provided new information on the lens biochemical changes. In the normal lens, we found nearly 10% of the total nonprotein thiols bound to the protein. There were two species of protein-thiol mixed disulfides, protein-GSH and protein-cysteine with the former 3-4 times higher than the latter. In the cataractous lens the mean value of some species was elevated two-fold whereas in the noncataractous pigmented lens both protein-thiol mixed disulfides were elevated but the protein-cysteine species showed more drastic increase (three-fold in one case and 13-fold in another case). It is therefore concluded that the formation of protein-thiol mixed disulfides may play a more critical role in cataractogenesis than does protein-protein disulfide formation.