Ganu V S, Shaw E
Int J Pept Protein Res. 1982 Nov;20(5):421-8. doi: 10.1111/j.1399-3011.1982.tb03062.x.
The activation of plasminogen results from proteolytic cleavage of the Arg560-Val561 bond by plasminogen activators (Sottrup-Jensen et al. PNAS (1975) 72, 2577). This region of the zymogen occurs in a small disulfide loop that must restrict the conformation around this bond. The nonapeptide sequence NH2-Cys-Pro-Gly-Arg-Val-Val-Gly-Gly-Cys-NH2 of plasminogen containing the activator sensitive arginyl valine bond was synthesized by carbodiimide coupling of Boc-Cys-Pro-Gly-OH(S-4-methylbenzyl) to NH2-Arg(NO2)-Val-Val-Gly-Gly-Cys-NH2(S-4-methylbenzyl), followed by HF treatment and K3Fe(CN)6 oxidation to form a disulfide bond. Purified peptide was not a substrate for urokinase (UK) or plasminogen activator (PA) but possessed a slightly inhibitory activity towards PA. Addition of a lysine to the N-terminus of the nonapeptide yielded a decapeptide sequence of plasminogen that was a better substrate for UK but not for PA. The decapeptide inhibits PA slightly but not UK. These results suggest that active site geometry for PA must be more restrictive than that of UK and that other regions may be involved in the productive interactions with the activators inducing a better fit of the cyclic peptide loop.
纤溶酶原的激活是由纤溶酶原激活剂对精氨酸560 - 缬氨酸561键进行蛋白水解切割而产生的（索特鲁普 - 延森等人，《美国国家科学院院刊》（1975年）72卷，2577页）。该酶原的这一区域存在于一个小的二硫键环中，这个环必定会限制该键周围的构象。通过将Boc - Cys - Pro - Gly - OH（S - 4 - 甲基苄基）与NH2 - Arg(NO2) - Val - Val - Gly - Gly - Cys - NH2（S - 4 - 甲基苄基）进行碳二亚胺偶联，随后进行氢氟酸处理和铁氰化钾氧化以形成二硫键，合成了含有激活剂敏感的精氨酰缬氨酸键的纤溶酶原九肽序列NH2 - Cys - Pro - Gly - Arg - Val - Val - Gly - Gly - Cys - NH2。纯化后的肽不是尿激酶（UK）或纤溶酶原激活剂（PA）的底物，但对PA具有轻微的抑制活性。在九肽的N端添加一个赖氨酸得到了纤溶酶原的十肽序列，该序列是UK更好的底物，但不是PA的底物。该十肽对PA有轻微抑制作用，但对UK没有抑制作用。这些结果表明，PA的活性位点几何结构比UK的更具限制性，并且其他区域可能参与与激活剂的有效相互作用，从而使环状肽环的契合度更好。
