Thiol protease which is believed to participate in intracellular degradation and turnover of proteins. Has also been implicated in tumor invasion and metastasis. The recombinant enzyme cleaves synthetic substrates with Phe and Leu (better than Val) in P2, with high specificity constant (kcat/Km) comparable to that of cathepsin L. High expression levels in heart, skeletal muscle, brain, testis and ovary; moderate levels in prostate, placenta, liver and colon; and no detectable expression in peripheral leukocytes and thymus. The disease is caused by variants affecting the gene represented in this entry. Belongs to the peptidase C1 family.