Takahashi T, Dehdarani A H, Yonezawa S, Tang J
J Biol Chem. 1986 Jul 15;261(20):9375-81.
The major cathepsin B isozyme CB-I purified from porcine spleens was studied for its specificity against various peptide and denatured protein substrates. The enzyme degraded all the peptide substrates by an exopeptidase activity. The substrates were degraded mainly by a dipeptidyl carboxypeptidase activity of the enzyme except for angiotensin I, from which a COOH-terminal leucine residue was released. The enzyme failed to hydrolyze peptides having a proline or cysteic acid in the COOH-terminal, penultimate, and antepenultimate positions. Reduced and carboxymethylated soybean trypsin inhibitor was degraded by the same dipeptidyl carboxypeptidase action of cathepsin B. No significant endopeptidase activity was observed. These results do not support the general assumption that cathepsin B has both endo- and exopeptidase activities, neither do these observations support the postulation that cathepsin B might be involved in the in vivo proteolytic processing of protein precursors. We propose that the biological role of this enzyme is mainly the degradation of tissue proteins in lysosomes.
对从猪脾脏中纯化得到的主要组织蛋白酶B同工酶CB-I，研究了其对各种肽和变性蛋白质底物的特异性。该酶通过外肽酶活性降解所有肽底物。除了血管紧张素I（从中释放出一个COOH末端亮氨酸残基）外，底物主要通过该酶的二肽基羧肽酶活性降解。该酶不能水解在COOH末端、倒数第二位和倒数第三位含有脯氨酸或半胱氨酸的肽。还原和羧甲基化的大豆胰蛋白酶抑制剂通过组织蛋白酶B相同的二肽基羧肽酶作用降解。未观察到明显的内肽酶活性。这些结果不支持组织蛋白酶B同时具有内肽酶和外肽酶活性的一般假设，这些观察结果也不支持组织蛋白酶B可能参与蛋白质前体的体内蛋白水解加工的假设。我们提出，这种酶的生物学作用主要是在溶酶体中降解组织蛋白。
