Tamaki T, Aoki N
J Biol Chem. 1982 Dec 25;257(24):14767-72.
During blood coagulation alpha 2-plasmin inhibitor (alpha 2PI) is cross-linked with fibrin by an activated fibrin-stabilizing factor (FSFa) plasma transglutaminase, activated coagulation factor XIII). When alpha 2PI was treated with FSFa in the absence of acceptor amino groups, the inhibitor lost more than 90% of its capacity to be cross-linked to fibrin because of hydrolysis of the gamma-carboxamides of FSFa-susceptible glutamine residues. Chemical modifications of the inhibitor's lysine epsilon-amino groups did not affect the cross-linking capacity of the inhibitor with fibrin, whereas the same chemical modifications in fibrinogen resulted in a remarkable loss of cross-linking capacity. These observations suggest that alpha 2PI plays a role as an acyl donor with its FSFa-susceptible glutamine residues in the cross-linking reaction with fibrin, and fibrin serves as an acyl acceptor with its lysine residues. The number of FSFa-susceptible glutamine residues/molecule of the inhibitor was estimated by measuring the maximum incorporation of [3H]histamine into the inhibitor and by analyzing the distribution of radioactivity in a tryptic digest of [14C]histamine-incorporated alpha 2PI.l It was found that each inhibitor molecule has one glutamine residue that is most susceptible to FSFa. When the radioactive histamine-incorporated inhibitor was reacted with excess amounts of plasmin, a small fragment carrying all the released radioactivity was rapidly released from the NH2-terminal part of the inhibitor moiety of the complex. The NH2-terminal amino acid sequence of the inhibitor was analyzed before and after treatment with FSFa or before and after incorporation of radioactive histamine. The glutamine residue at the second position from the NH2-terminal end was converted to a glutamic acid residue when the inhibitor was treated with FSFa. When the radioactive histamine-incorporated inhibitor ws analyzed, the radioactivity was found predominantly at the second position from the NH2-terminal end. These results indicate that the glutamine residue susceptible to FSFa in alpha 2PI is located next to the NH2-terminal residue.
在血液凝固过程中，α2 - 纤溶酶抑制剂（α2PI）通过活化的纤维蛋白稳定因子（FSFa，血浆转谷氨酰胺酶，即活化的凝血因子 XIII）与纤维蛋白交联。当α2PI在没有受体氨基的情况下用FSFa处理时，由于FSFa敏感的谷氨酰胺残基的γ - 羧酰胺水解，该抑制剂失去了超过90%与纤维蛋白交联的能力。抑制剂赖氨酸ε - 氨基的化学修饰不影响其与纤维蛋白的交联能力，而纤维蛋白原中相同的化学修饰则导致交联能力显著丧失。这些观察结果表明，α2PI在与纤维蛋白的交联反应中，以其对FSFa敏感的谷氨酰胺残基作为酰基供体，而纤维蛋白则以其赖氨酸残基作为酰基受体。通过测量[3H]组胺在抑制剂中的最大掺入量，并分析[14C]组胺掺入的α2PI胰蛋白酶消化物中的放射性分布，估算出抑制剂每个分子中对FSFa敏感的谷氨酰胺残基数量。结果发现每个抑制剂分子有一个对FSFa最敏感的谷氨酰胺残基。当放射性组胺掺入的抑制剂与过量的纤溶酶反应时，一个携带所有释放放射性的小片段迅速从复合物抑制剂部分的NH2末端释放出来。在FSFa处理前后或放射性组胺掺入前后分析抑制剂的NH2末端氨基酸序列。当抑制剂用FSFa处理时，从NH2末端起第二个位置的谷氨酰胺残基转化为谷氨酸残基。当分析放射性组胺掺入的抑制剂时，发现放射性主要位于从NH2末端起第二个位置。这些结果表明，α2PI中对FSFa敏感的谷氨酰胺残基位于NH2末端残基旁边。
