– Thiol protease involved in osteoclastic bone resorption. Displays potent endoprotease activity against fibrinogen at acid pH. May play an important role in extracellular matrix degradation. Involved in the release of thyroid hormone thyroxine (T4) by limited proteolysis of TG/thyroglobulin in the thyroid follicle lumen. Cathepsin K Protein, Mouse, Recombinant (His) is expressed in E. coli expression system with N-6xHis tag. The predicted molecular weight is 27.4 kDa and the accession number is P55097.