Cathepsin X (EC 3.4.18.1, cathepsin B2, cysteine-type carboxypeptidase, cathepsin IV, cathepsin Z, acid carboxypeptidase, lysosomal carboxypeptidase B) is an enzyme. This enzyme catalyses the following chemical reaction Cathepsin X (EC 3.4.18.1, cathepsin B2, cysteine-type carboxypeptidase, cathepsin IV, cathepsin Z, acid carboxypeptidase, lysosomal carboxypeptidase B) is an enzyme. This enzyme catalyses the following chemical reaction Cathepsin X is a lysosomal cysteine peptidase of family C1 (papain family).