DiScipio R G
Biochem J. 1981 Dec 1;199(3):497-504. doi: 10.1042/bj1990497.
The cleavage of human complement component C5 to fragment C5b by the alternative pathway C5 convertase was studied. The alternative-pathway C5 convertase on zymosan can be represented by the empirical formula zymosan--C3b2BbP. Both properdin-stabilized C3 and C5 convertase activities decay with a half life of 34 min correlating with the loss of the Bb subunit. The C5 convertase functions in a stepwise fashion: first, C5 binds to C3b and this is followed by cleavage of C5 to C5b. The capacity to bind C3b is a stable feature of component C5, as C5b also has this binding capacity. Component C5, unlike component C3, does not form covalent bonds with zymosan after activation, and C5 is not inhibited by amines. Therefore C5, although similar in structure to C3, does not appear to contain the internal thioester group reported for C3 and C4.
研究了通过替代途径C5转化酶将人补体成分C5裂解为片段C5b的过程。酵母聚糖上的替代途径C5转化酶可用经验公式酵母聚糖--C3b2BbP表示。备解素稳定的C3和C5转化酶活性均以34分钟的半衰期衰减，这与Bb亚基的丧失相关。C5转化酶以逐步方式发挥作用：首先，C5与C3b结合，随后C5裂解为C5b。结合C3b的能力是成分C5的一个稳定特性，因为C5b也具有这种结合能力。与成分C3不同，成分C5在激活后不与酵母聚糖形成共价键，且C5不受胺类抑制。因此，C5虽然在结构上与C3相似，但似乎不含有报道的C3和C4中的内部硫酯基团。
