Seya T, Nagasawa S, Matsukura M, Hasegawa H, Atkinson J P
Complement. 1985;2(2-3):165-74. doi: 10.1159/000467857.
In the breakdown of fluid phase C3 in plasma, the process of conversion of iC3b to C3c and 'C3d' has not been elucidated. Using fluorescent labeled iC3b as a substrate, urokinase (UK) treated but not normal plasma was found to exhibit effective 'C3d' production. To address the relationship between the fibrinolytic activity specific for UK-activated plasma and this 'C3d' production, an assay system was developed that permitted the simultaneous determination of both activities. This method indicated that 'C3d' generation paralleled that of plasmin-dependent fibrinogen degradation. A Km of iC3b for plasmin was 3.0 X 10(-6) mol/l which is similar to the Km of fibrinogen. Plasmin cleavage of iC3b gave rise to C3d1 (Mr 42,000) and C3d2 (Mr 28,000). Purified plasmin C3d1 showed the same Mr and pI as C3d,g prepared from iC3b, by H and I. C3d2 was derived from C3d1. From these in vitro experiments with urokinase-treated plasma, we conclude that in parallel with fibrinolysis efficient cleavage of fluid phase iC3b to C3c + C3d,g and C3d occurs and we hypothesize that this is one mechanism for the generation of C3d in vivo.
在血浆中液相C3的分解过程中，iC3b转化为C3c和“C3d”的过程尚未阐明。以荧光标记的iC3b为底物，发现经尿激酶（UK）处理而非正常的血浆能有效产生“C3d”。为了研究UK激活血浆的纤溶活性与这种“C3d”产生之间的关系，开发了一种可同时测定这两种活性的检测系统。该方法表明，“C3d”的产生与纤溶酶依赖性纤维蛋白原降解的产生平行。纤溶酶作用于iC3b的Km为3.0×10⁻⁶mol/L，这与纤维蛋白原的Km相似。纤溶酶对iC3b的切割产生了C3d1（分子量42,000）和C3d2（分子量28,）。纯化的纤溶酶C3d1与通过H和I从iC3b制备的C3d,g具有相同的分子量和等电点。C3d2源自C3d1。通过对尿激酶处理血浆的这些体外实验，我们得出结论，与纤维蛋白溶解同时，液相iC3b高效切割为C3c + C3d,g和C3d发生，并且我们推测这是体内产生C3d的一种机制。
