Cathepsin E(cath E) is an intracellular aspartic protease that is mainly present in the immune system.Cath E is highly homologous to the analogous aspartic protease cathepsin D(cath D).So far,the physiological function of cath E has not been completely understood and a wide variety of inhibitors are used to study it.Because of the non-specificity and difficulty in purification or preparation,none of them are available in quantities suffiicient for functional studies.