EC - Cathepsin X

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IntEnz Enzyme Nomenclature


Accepted name:
cathepsin X
Other names:
acid carboxypeptidase
cathepsin B2
cathepsin IV
cathepsin Z
cysteine-type carboxypeptidase
lysosomal carboxypeptidase B
Systematic name:



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.

Links to other databases

Enzymes and pathways: NC-IUBMB , BRENDA , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , MEROPS , UniPathway
Structural data: CSA , EC2PDB
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: 12648-12654 (1999). [PMID: 10504234]
  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: 135-139 (1998). [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: 16816-16823 (1998). [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: 1269-1276 (1975). [PMID: 577]
  5. Otto, K. and Riesenkönig H.
    Improved purification of cathepsin B1 and cathepsin B2.
    Biochim. Biophys. Acta 379: 462-475 (1975). [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: 308-321 (1974). [PMID: 4429705]

[EC created 1981, modified 2000]