Limited proteolysis of bovine lens α-crystallin by calpain, A Ca2+-dependent cysteine proteinase, isolated from the same tissue

摘要: Abstract A Ca 2+ -dependent cysteine proteinase (calpain, EC 3.4.22.17) was found in the cytosolic fraction of bovine lens and purified to apparent homogeneity. The enzyme required 1 mM for its full activation composed two subunits M r 80 000 29 as demonstrated by polyacrylamide gel electrophoresis presence sodium dodecyl sulfate (SDS). This enzyme, when activated , degraded both A- B-chains α-crystallin, which were isolated also from lens. SDS-gel digest revealed that A-chain ( 19 000) broken down produce an 18-kDa polypeptide fragment B-chain 22 500) a 19.50kDa fragment. No further cleavage occurred even upon prolonged incubation or after second addition indicating uniquely limited each chain protein. existence calpastatin, endogenous inhibitor protein specific calpain, cytosol.