THE HUMAN-COMPLEMENT SYSTEM - ASSEMBLY OF THE CLASSICAL PATHWAY C-3 CONVERTASE
THE HUMAN-COMPLEMENT SYSTEM - ASSEMBLY OF THE CLASSICAL PATHWAY C-3 CONVERTASE
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DOI：
10.1042/bj1890173
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发表时间：
1980-01-01
影响因子：
4.1
通讯作者：
KERR, MA
中科院分区：
文献类型：
--
作者：
KERR, MA
研究了[人]经典途径C3 [补体成分3]转化酶在液相中的组装。这种酶是由C2和C4在C.hivin.1s切割这些蛋白质时组装而成的。一旦组装，酶活性迅速衰减。获得了动力学证据，表明这种衰减甚至比以前提出的更快（在37 ℃时K衰减为2.0 min-1）。C）。结果，最佳的C3转化酶活性仅在高C.hivin.1s水平下观察到，这导致C2的快速切割速率和C3转化酶形成速率的增加。在较低温度（22 ℃）下使用高浓度的C.hivin.1s。C）在过量底物存在下，动力学证明该酶包含C4 b和裂解的C2的等摩尔复合物。从凝胶过滤实验中获得了C2 a作为酶的催化亚基的作用的直接证据。C2b似乎在pH 8.5和低离子强度下介导C4（或C4 b）和C2之间的相互作用，其中可以容易地检测到相互作用。它在酶的组装中可能是重要的，尽管它不参与催化活性。C3转化酶的衰减反映了C2 a从C4 b中的释放。碘对C3转化酶的稳定作用显然是稳定C4 b·C2 a相互作用的作用，否则这种作用很弱。C.hivin.1s不是C3转化酶的一部分。
The assembly of the [human] classical pathway C3 [complement component 3] convertase in the fluid phase was studied. The enzyme is assembled from C2 and C4 on cleavage of these proteins by C.hivin.1s. Once assembled, the enzyme activity decays rapidly. Kinetic evidence was obtained that this decay is even more rapid than previously suggested (Kdecay is 2.0 min-1 at 37.degree. C). As a result, optimal C3 convertase activity is only observed with high C.hivin.1s levels, which result in rapid rates of cleavage of C2 and increased rates of formation of the C3 convertase. Using high concentrations of C.hivin.1s at lower temperatures (22.degree. C) in the presence of excess substrate, it was kinetically demonstrated that the enzyme comprises an equimolar complex of C4b and cleaved C2. Direct evidence was obtained from gel-filtration experiments for the role of C2a as the catalytic subunit of the enzyme. C2b appears to mediate the interaction between C4 (or C4b) and C2 at pH 8.5 and at low ionic strength where the interactions can easily be detected. It may be important in the assembly of the enzyme, although it is not involved in the catalytic activity. The decay of the C3 convertase reflects the release of C2a from the C4b.cntdot.(C2b).cntdot.C2a complex; the stabilizing effect of iodine on the C3 convertase is apparently one of stabilizing the C4b.cntdot.C2a interaction, which is otherwise weak. C.hivin.1s is not a part of the C3 convertase enzyme.