Kumazaki T, Ishii S, Yokosawa H
Department of Biochemistry, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo.
J Biochem. 1994 Oct;116(4):787-93. doi: 10.1093/oxfordjournals.jbchem.a124597.
A trypsin inhibitor from hemolymph of the solitary ascidian, Halocynthia roretzi, has been reported to be present in two forms, ATI-I and ATI-II. ATI-I consists of a single polypeptide chain with a unique sequence of 55 amino acid residues, while ATI-II has two chains that seem to be derived from ATI-I by cleavage at the Lys16-Met17 bond [Kumazaki, T., Hoshiba, N., Yokosawa, H., and Ishii, S. (1990) J. Biochem. 107, 409-413]. ATI-II (as modified inhibitor) was proved to be produced by incubation of ATI-I (as virgin inhibitor) with a catalytic amount of bovine trypsin. The tryptic hydrolysis at the Lys16-Met17 bond in virgin inhibitor showed a maximum velocity at around pH 3.5. On the other hand, acid treatment of a complex prepared by mixing equimolar quantities of trypsin and the the modified inhibitor yielded free trypsin and the virgin inhibitor. The results of chemical analyses indicated that the Lys16-Met17 bond that had been cleaved in ATI-II was resynthesized by the acid treatment. These findings strongly suggest that the Lys16-Met17 bond is the reactive site of ATI for trypsin.
据报道，来自独居海鞘（Halocynthia roretzi）血淋巴的一种胰蛋白酶抑制剂以两种形式存在，即ATI-I和ATI-II。ATI-I由一条含有55个氨基酸残基独特序列的单一多肽链组成，而ATI-II有两条链，似乎是通过在Lys16-Met17键处切割从ATI-I衍生而来[熊崎，T.，星场，N.，横泽，H.，石井，S.（1990年）《生物化学杂志》107卷，409 - 413页]。已证明，将ATI-I（作为原始抑制剂）与催化量的牛胰蛋白酶一起孵育可产生ATI-II（作为修饰抑制剂）。原始抑制剂中Lys16-Met17键处的胰蛋白酶水解在pH 3.5左右显示出最大速度。另一方面，用等摩尔量的胰蛋白酶和修饰抑制剂混合制备的复合物进行酸处理，可得到游离胰蛋白酶和原始抑制剂。化学分析结果表明，在ATI-II中被切割的Lys16-Met17键通过酸处理重新合成。这些发现有力地表明，Lys16-Met17键是ATI对胰蛋白酶的反应位点。
