Cathepsin C is a lysosomal cysteine protease with broad exopeptidase activity that progressively removes dipeptides from various protein and polypeptides substrates. Aside from its role in post-translational processing, cathepsins may also participate in apoptotic signaling pathways by targeting cytosolic caspases and proapoptotic proteins. Gly-Phe-beta-naphthylamide is a substrate of cathepsin C that accumulates within the lysosome. Hydrolysis by cathepsin C degrades Gly-Phe-beta-naphthylamide into fragments that do not easily diffuse through the lysosomal membrane, leading to a loss of lysosome membrane integrity. This compound has been used to study intralysosomal hydrolysis, lysosomal membrane permeability, and the function of cathepsin C. At 50 µM, Gly-Phe-beta-naphthylamide can inhibit the cathepsin-dependent activation of caspase-8.