Takahashi T, Dehdarani A H, Tang J
Laboratory of Protein Studies, Oklahoma Medical Research Foundation, Oklahoma City 73104.
J Biol Chem. 1988 Aug 5;263(22):10952-7.
Cathepsin H purified from porcine spleens was studied for its specificity against various peptide and denatured protein substrates. The enzyme degraded all peptide substrates exclusively by an aminopeptidase activity. The enzyme preferentially released NH2-terminal amino acid residues with large hydrophobic (Phe, Trp, Leu, and Tyr) or basic (Arg and Lys) side chains. Amino acids containing small or polar side chains were not released. Peptides with a proline in the NH2-terminal or penultimate positions were not hydrolyzed either. Large polypeptides such as reduced and carboxymethylated soybean trypsin inhibitor and aldolase were not degraded. These results indicate that cathepsin H is an exopeptidase but not an endopeptidase. We propose that the biological role of this enzyme is the degradation of tissue proteins in lysosomes by its aminopeptidase activity.
对从猪脾脏中纯化得到的组织蛋白酶H针对各种肽和变性蛋白质底物的特异性进行了研究。该酶仅通过氨肽酶活性降解所有肽底物。该酶优先释放具有大的疏水（苯丙氨酸、色氨酸、亮氨酸和酪氨酸）或碱性（精氨酸和赖氨酸）侧链的NH2末端氨基酸残基。含有小的或极性侧链的氨基酸不会被释放。在NH2末端或倒数第二个位置含有脯氨酸的肽也不会被水解。大的多肽，如还原型和羧甲基化的大豆胰蛋白酶抑制剂和醛缩酶，不会被降解。这些结果表明组织蛋白酶H是一种外肽酶而非内肽酶。我们认为该酶的生物学作用是通过其氨肽酶活性在溶酶体中降解组织蛋白。
