Table 1. Human cathepsin isoforms.
| Species | Protein family | Number of amino acids (aa) | EC No. | Location |
|---|---|---|---|---|
| Cathepsin A | 480 | 3.4.16.5 | Brain, skin, placenta, platelet, liver | |
| Cathepsin G | 225 | 3.4.21.2 | Skin, monocytes, neutrophils | |
| Cathepsin D | 412 | 3.4.23.5 | Spleen, kidney, liver, melanoma, plasma, platelets | |
| Cathepsin E | 401 | 3.4.23.34 | Brain, intestine, stomach, Erythrocytes, lymph nodes, skin, spleen, lung |
|
| Cathepsin B | 339 | 3.4.22.1 | Liver, kidney, thyroid gland, spleen | |
| Cathepsin C | 463 | 3.4.14.1 | Lung, spleen, kidney, placenta, cytotoxic T lymphocytes | |
| Cathepsin F | 484 | 3.4.22.41 | Brain, heart, skeletal muscle, testis, ovary, macrophages | |
| Cathepsin H | 335 | 3.4.22.16 | Liver, kidney, spleen | |
| Cathepsin K | 329 | 3.4.22.38 | Osteoclasts, macrophages, epithelial cells of the gastrointestinal, respiratory and urinary tracts in human embryos and fetuses, lung | |
| Cathepsin L | 333 | 3.4.22.15 | Liver, thyroid gland, kidney | |
| Cathepsin O | 321 | 3.4.22.42 | Liver, kidney, placenta, ovary | |
| Cathepsin S | 331 | 3.4.22.27 | Spleen, lymph nodes, antigen-presenting cells, heart | |
| Cathepsin V | 334 | 3.4.22.43 | Cornea, testes, thymus | |
| Cathepsin W | 376 | 3.4.22.- | Spleen, lymph nodes (specifically cytotoxic T lymphocytes) | |
| Cathepsin X | 303 | 3.4.18.1 | Liver, kidney, placenta, lung |