A VARIETY OF CALPAIN CALPASTATIN SYSTEMS IN MAMMALIAN ERYTHROCYTES

Calpain and its endogenous inhibitor, calpastatin, were isolated from erythrocytes of various mammals and their properties were compared. It has been widely believed that mammalian erythrocytes contain only A-calpain. However, rat and human erythrocytes were found to contain two species of calpain, identified as mu-calpain and m-calpain from their elution positions on DEAE-cellulose column chromatography and their Ca2+-requirements. Thus, it is apparent that rat and human erythrocytes contain not only mu-calpain, but m-calpain as well. On the other hand, rabbit erythrocytes contain only mu-calpain. Western blot analysis showed that human and rabbit erythrocytes contain predominantly 70-kDa calpastatin (erythrocyte-type), but unnegligible amounts of 110-kDa calpastatin (tissue-type) are also present. Rat erythrocytes were shown to contain a calpastatin with a molecular mass of approx. 100 kDa almost exclusively; this molecular mass was in perfect coincidence with the mass of the calpastatin in rat lung. These results strongly suggest that rat erythrocytes contain a tissue-type calpastatin. No essential change in the calpain/calpastatin system during maturation of rabbit reticulocytes into mature erythrocytes was observed.