CTSK(cathepsin K), also named as CTSO, CTSO2, is a recently identified lysosomal cysteine proteinase. CTSK is synthesized as a proenzyme of 38 kDa and subsequently enters acidic lysosomal compartments, in which the propeptide is cleaved and transformed into an active enzyme and it may influence adipocyte differentiation through modifying extracellular matrix components(PMID:16912123). It is revealed both the 46-kDa cathepsin-K precursor and the 30-kDa mature form in mouse bone extracts(PMID:9811821). The high CTSK protein levels are only detected in primary cultured fibroblasts derived from normal and neoplastic breast tissue, where the 37- and 25-kDa bands to be detected correspond to pro- and mature proteins through western blot(PMID:18765527). The full length protein has a signal peptides with 15 amino acids and a propeptide with 99 amino acids. This antibody is specific to CTSK.