Important for the overall degradation of proteins in lysosomes. Hydrolysis of proteins, acting as an aminopeptidase (notably, cleaving Arg-|-Xaa bonds) as well as an endopeptidase. Composed of a mini chain and a large chain. The large chain may be split into heavy and light chain. All chains are held together by disulfide bonds. Widely expressed with highest expression found in non-skeletal tissues. Low levels found in skeletal tissue. Mice exhibit markedly abnormal posterior chamber of eyeball with a configuration suggestive of increased axial lengthening, compared to the rounded appearance in wild-type littermates. Belongs to the peptidase C1 family.