Inhibition of the proteolysis of rat erythrocyte membrane proteins by a synthetic inhibitor of calpain

A synthetic inhibitor of calpain protects rat erythrocyte membrane-associated cytoskeletal proteins from proteolytic degradation (IC50 = 1 microM) which occurs when the cells are rendered permeable to Ca++. Leupeptin, a naturally occurring inhibitor of the enzyme, does not afford any protection at concentrations up to 100 microM.