IUBMB Enzyme Nomenclature


Accepted name: cathepsin X

Reaction: Release of C-terminal amino acid residues with broad specificity, but lacks action on C-terminal proline. Shows weak endopeptidase activity

Other names: cathepsin B2; cysteine-type carboxypeptidase; cathepsin IV; cathepsin Z; acid carboxypeptidase; lysosomal carboxypeptidase B

Comments: Cathepsin X is a lysosomal cysteine peptidase of family C1 (papain family). The pH optimum is dependent on the substrate and is 5.0 for the carboxypeptidase activity. Unstable above pH 7.0. Compound E-64, leupeptin and antipain are inhibitors, but not cystatin C. Cathepsin X is ubiquitously distributed in mammalian tissues. The propeptide is extremely short (38 amino acid residues) and the proenzyme is catalytically active. Human gene locus: 20q13. Formerly EC, cysteine-type carboxypeptidase

Links to other databases: BRENDA, EXPASY, KEGG, MEROPS, Metacyc, PDB, CAS registry number: 37217-21-3


1. Nägler, D.K., Zhang, R., Tam, W., Sulea, T., Purisima, E.O., and Ménard, R. Human cathepsin X: A cysteine protease with unique carboxypeptidase activity. Biochemistry 38 (1999) 12648-12654. [PMID: 9642240]

2. Nägler, D.K. and Ménard, R. Human cathepsin X: A novel cysteine protease of the papain family with a very short proregion and unique insertions. FEBS Lett. 434 (1998) 135-139. [PMID: 9738465]

3. Santamaría, I. Velasco, G., Pendás, A.M., Fueyo, A. and López-Otín, C. Cathepsin Z, a novel human cysteine proteinase with a short propeptide domain and a unique chromosomal location. J. Biol. Chem. 273 (1998) 16816-16823. [PMID: 9642240]

4. McDonald J.K. and Ellis, S. On the substrate specificity of cathepsins B1 and B2 including a new fluorogenic substrate for cathepsin B1. Life Sci. 17 (1975) 1269-1276. [PMID: 577]

5. Otto, K. and Riesenkönig H. Improved purification of cathepsin B1 and cathepsin B2. Biochim. Biophys. Acta 379 (1975) 462-475. [PMID: 1122298]

6. Ninjoor, V., Taylor, S.L. and Tappel, A.L. Purification and characterization of rat liver lysosomal cathepsin B2. Biochim. Biophys. Acta 370 (1974) 308-321. [PMID: 4429705]

[EC created 1981, modified 2000]

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