E-64 is a potent and irreversible inhibitor of cysteine proteases, making it widely used in biochemical and biomedical research. It is commonly applied to prevent protein degradation in cell lysates and tissue extracts by inhibiting enzymes like cathepsins, calpains, and papain. This property makes E-64 valuable in studies involving protein turnover, apoptosis, and lysosomal function. In cell culture, E-64 is used to investigate the role of cysteine proteases in cellular processes such as autophagy and necrosis. It also serves as a tool in parasitology, where it helps block protease activity in parasites like Plasmodium and Trypanosoma, aiding in the study of parasite invasion and development. Due to its specificity, E-64 is employed in enzyme kinetics and mechanistic studies to characterize cysteine protease activity. It is also used in diagnostic applications where uncontrolled protease activity can interfere with assay results.