Aprotinin

Aprotinin, also known as pancreatic trypsin inhibitor and trypsin-kallikrein inhibitor, is a monomeric polypeptide of 58 amino acids found in a number of organs, including lungs, spleen, liver, and pancreas. It is also detectable in a free form in calf serum. It is a competitive inhibitor that forms a loose complex with serine proteases and blocks their active centers. The complex exhibits many interactions between protease and inhibitor. The trypsin-aprotinin complex, for example, does not dissociate at a concentration of 8 M uric acid or 6 M guanidine hydrochloride. Aprotinin is only cleaved slowly by most proteases, with the exception of thermolysin at temperatures >+60°C. Its unique structure is responsible for the molecule’s high stability and remarkable resistance to elevated temperatures, acids, and proteases.

抑肽酶被大量用作胰蛋白酶抑制剂。

抑肽酶是一种竞争性丝氨酸蛋白酶抑制剂，可与酶的活性位点组成稳定的复合酶并同时对其进行封闭。 这种结合是可逆的，而且绝大多数抑肽酶-蛋白酶复合物可在极端的pH >10 or < 3水平时发生解离。 从结构上来说，抑肽酶是一种来自牛肺的单体球状蛋白，由58个氨基酸组成并排列在具有三个交联二硫键的单个多肽链中。

一个胰蛋白酶抑制剂单位（TIU）可将两个胰蛋白酶单位的活性降低50％，而其中一个胰蛋白酶单位在pH 7.8和25℃下可每分钟水解1.0 μ摩尔的N-α-苯甲酰基-DL-精氨酸对硝基苯胺。另一种常用的单位是KIU，而1 TIU = 1,300 KIU。

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