Although
cataracts are a well-known age-related disease, the mechanism of their formation is not well understood. It is currently thought that eye lens
proteins become abnormally aggregated, initially causing clumping that scatters the light and interferes with focusing on the retina, and ultimately resulting in a
cataract. The abnormal aggregation of
lens proteins is considered to be triggered by various post-translational modifications, such as oxidation, deamidation, truncation and isomerization, that occur during the aging process. Such modifications, which are also generated by
free radical and
reactive oxygen species derived from γ-irradiation, decrease
crystallin solubility and lens transparency, and ultimately lead to the development of a
cataract. In this study, we irradiated young rat
lenses with low-dose γ-rays and extracted the water-soluble and insoluble
protein fractions. The water-soluble and water-insoluble
lens proteins were digested with
trypsin, and the resulting
peptides were analyzed by LC-MS. Specific oxidation sites of
methionine,
cysteine and
tryptophan in rat water-soluble and -insoluble γE and γF-
crystallin were determined by one-shot analysis. The oxidation sites in rat γE and γF-
crystallin resemble those previously identified in γC and γD-
crystallin from human age-related
cataracts. Our study on modifications of
crystallins induced by ionizing irradiation may provide useful information relevant to human senile
cataract formation.