Calpain II in human lens.

The purposes of the current study were to: determine if human lenses contain calpain II (EC.34.22.17) activity, measure the effect of aging and anatomical location on lens calpain II activity, and determine if human lenses contain the endogenous calpain inhibitor calpastatin. Both enzymatic and immunologic assays indicated that human lenses contained calpain II activity. Calpain II activity was highest in the cortex of lenses from young donors, and lowest in the nucleus of aged lenses, where it was sometimes nondetectable. In some cases, calpain II activity persisted in the nucleus of lenses from donors greater than 70 years of age. Human lenses also contained endogenous calpain inhibitor (calpastatin) in excess over calpain enzymatic activity. Calpastatin activity did not decrease during aging. Although human lenses contained approximately 3% of the calpain activity found in rat lenses, calpain II may still be a major endopeptidase in human lenses. Demonstration of calpain II in human lenses suggested that calpain II could be involved in both lens maturation and cataract formation.