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蚯蚓纤溶酶原激活剂（ｅ－ＰＡ）具有多种底物特异性．对构成其的小亚基的活性中心的研究有利于阐述ｅ－ＰＡ的结构与功能的关系．利用胰蛋白酶的特异性抑制剂ＴＬＣＫ（Ｎ－α－ｐ－ｔｏｓｙｌ－Ｌ－ｌｙｓｉｎｅｃｈｌｏｒｏｍｅｔｈｙｌｋｅｔｏｎｅ）对小亚基进行抑制活性的研究，结果表明ＴＬＣＫ对酶促反应的抑制曲线与可逆抑制曲线相似，但在抑制剂存在下的最大反应速度与抑制剂不存在时的最大反应速度不同．结合小亚基在ＴＬＣＫ存在下的ＣＤ光谱变化，证明了小亚基分子表面存在两个活性位点，这两个活性位点对ＴＬＣＫ的敏感性不同，从而造成ＴＬＣＫ抑制行为的异常．推测不同的活性结构对应于不同的底物特异性．
Earthworm plasminogen activator (e-PA) has a variety of substrate specificities. The study of the active site of its small subunit is helpful to elucidate the relationship between structure and function of e-PA. The inhibitory activity of the small subunit was investigated by the trypsin-specific inhibitor TLCK (N-α-p-tosyl-L-lysinechloromethylketone). The results showed that the inhibition curve of TLCK was similar to that of the reversible inhibition curve, The maximum reaction rate in the presence of an inhibitor is different from the maximum reaction rate in the absence of an inhibitor. Combined with the change of CD spectra of small subunit in the presence of TLCK, it was proved that there are two active sites on the surface of small subunit. The sensitivity of these two active sites to TLCK is different, resulting in the abnormality of TLCK inhibition. It is speculated that different active structures correspond to different substrate specificities.