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The distribution of glutathione-S-transferase (GST) activity was determined in frozen normal human lenses. The highest activity of GST was found in the peripheral and equatorial regions, whereas the lowest activity was found in the nucleus. Western blot showed that both mu and pi isoenzymes of GST were present in human lenses. This result is similar to that found in rat lenses. In addition, GST activity was analyzed in 50 lens epithelia which were obtained during cataract surgery. Twenty-seven lens epithelia showed no activity. Statistically significant association was found between cortical and mixed cortical--nuclear cataract and loss of GST activity. No association was found between pure nuclear cataract and loss of epithelial GST activity.

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.

Lens proteins from the guinea pig (Cavia porcellus) were found to be similar to those of other mammals with the exception of the presence of a previously undescribed constituent comprising about 10% of the total soluble lens proteins. This oligomeric protein is composed of polypeptides with apparent molecular weight of 38,000 and elutes from gel exclusion chromatography columns in the beta H-crystallin fraction. Following purification by ion exchange chromatography an antibody was raised against the protein. Using that antibody and antibodies specific for other crystallins we could detect no cross-reactivity between the guinea pig protein and any other reported lens crystallin. This protein, which we have named zeta (zeta)-crystallin, is the first reported mammalian lens crystallin which is not part of the alpha- or beta-gamma families of crystallins. Unlike all other known mammalian crystallins, which have little or no alpha-helical structure, zeta-crystallin is estimated to be approximately 30-40% alpha-helix.