Robinson B R, Houng A K, Reed G L
Harvard School of Public Health, Harvard Medical School and Massachusetts General Hospital, Boston, MA, 02115, USA.
Circulation. 2000 Sep 5;102(10):1151-7. doi: 10.1161/01.cir.102.10.1151.
Because the increased fibrinolytic resistance of older thrombi may be caused by the continuous cross-linking action of fibrin-bound activated factor XIII (FXIIIa), we examined the persistence of FXIIIa catalytic activity in clots of various ages.
The time-related changes in FXIIIa activity in clots was measured with (1) alpha(2)-antiplasmin (alpha(2)AP), a physiological glutamine substrate; (2) alpha(2)AP(13-24), a peptide; and (3) pentylamine, a nonspecific lysine substrate. The cross-linking of alpha(2)AP, alpha(2)AP(13-24), and pentylamine into fibrin by clot-bound FXIIIa declined rapidly with half-lives of 19, 21, and 26 minutes, respectively. Mutational studies showed that glutamine 14 (but not glutamine 3 or 16) and valine 17 of alpha(2)AP(13-24) were required for efficient cross-linking to fibrin. The loss of activity was not due primarily to FXIIIa proteolysis and was partially restored by reducing agents, suggesting that oxidation contributes to the loss of the enzyme's activity in clots. In vivo, the ability of thrombus-bound FXIIIa to cross-link an infused alpha(2)AP(13-24) peptide into existing pulmonary emboli also declined significantly over time.
FXIIIa cross-links alpha(2)AP and an alpha(2)AP peptide, in a sequence-specific manner, into formed clots with a catalytic half-life of approximately 20 minutes. This indicates that FXIIIa activity is a hallmark of new thrombi and that the antifibrinolytic cross-linking effects of FXIIIa are achieved more rapidly in thrombi than previously believed.
由于老化血栓中纤溶抗性增加可能是由纤维蛋白结合的活化因子 XIII（FXIIIa）的持续交联作用引起的，我们研究了不同年龄凝块中 FXIIIa 催化活性的持续性。
使用（1）α2 - 抗纤溶酶（α2AP），一种生理性谷氨酰胺底物；（2）α2AP(13 - 24)，一种肽；以及（3）戊胺，一种非特异性赖氨酸底物，测定凝块中 FXIIIa 活性随时间的变化。凝块结合的 FXIIIa 将 α2AP、α2AP(13 - 24)和戊胺交联到纤维蛋白中的过程迅速下降，半衰期分别为 19、21 和 26 分钟。突变研究表明，α2AP(13 - 24)的谷氨酰胺 14（而非谷氨酰胺 3 或 16）和缬氨酸 17 是有效交联到纤维蛋白所必需的。活性丧失并非主要由于 FXIIIa 的蛋白水解作用，还原剂可部分恢复其活性，这表明氧化作用导致了凝块中该酶活性的丧失。在体内，血栓结合的 FXIIIa 将注入的 α2AP(13 - 24)肽交联到现有的肺栓塞中的能力也随时间显著下降。
FXIIIa 以序列特异性方式将 α2AP 和一种 α2AP 肽交联到形成的凝块中，催化半衰期约为 20 分钟。这表明 FXIIIa 活性是新血栓的一个标志，并且 FXIIIa 的抗纤溶交联作用在血栓中比之前认为的实现得更快。
