Cathepsins J and K: high molecular weight cysteine proteinases from human tissues

Human tissue extracts contained two high Mr proteinases active in hydrolyzing the fluorogenic substrate Cbz-phe-arg-aminomethylcoumarin. By gel filtration chromatography, cathepsins J and K had apparent molecular weights of 230,000 and 650,000, respectively. Both enzymes were cysteine proteinases with optimum activity at pH 6.2-6.8; neither had aminopeptidase activity. Human kidney, lung and spleen were rich sources of these enzymes, while liver contained moderate amounts. Cathepsins J and K were partially characterized and appeared to differ from the mammalian high Mr cysteine proteinases described in the literature. In rat liver and kidney and in mouse liver, cathepsin J was localized in the particulate fraction, whereas cathepsin K was not detected in these tissues.