Degradation of actin and vimentin by calpain II, a Ca2+‐dependent cysteine proteinase, in bovine lens

Abstract
Calpain II, a high Ca2+-requiring form of Ca2+-dependent cysteine proteinase (EC 3.4.22.17), isolated from bovine lens was found to cleave actin and vimentin, two major cytoskeletal elements of the lens. Polyacrylamide gel electrophoresis revealed that actin (Mr 43000) was broken down through intermediary products of approximate Mr 42000 and 40000, while vimentin (Mr 57000) was rapidly cleaved into several fragments ranging from Mr 44000 to 20000. The cleavage was dependent on Ca2+ and could be blocked by calpastatin, a calpain-specific inhibitor. These findings suggest that calpain might play a role in age-related degradation of the lens cytoskeleton