Cathepsins are usually characterized as members of the lysosomal cysteine protease (active site) family and the cathepsin family name has been synomonous with lysosomal proteolytic enzymes. In actuality, the cathepsin family also contains members of the serine protease (cathepsin A,G) and aspartic protease (cathepsin D,E) families as well.
These enzymes exist in their processed form as disulfide-linked heavy and light chain subunits with molecular weights ranging from 20-35 kDa. Cathepsin C is the noted exception, existing as an oligomeric enzyme with a MW ~200 kDa. Initially synthesized as inactive zymogens, they are post-translationally processed into their active configurations after passing through the endoplasmic reticulum and subsequent incorporation into the acidic environment of the lysosomes.
Protease activity can be detected within whole living cells using Neuromics’ Magic Red™ substrate-based assay kits. Designated as the MR-Cathepsin product line, these kits allow researchers to quickly visualize intracellular cathepsin activity within their particular experimental cell line.