Lakatos S
Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest.
Biochem Biophys Res Commun. 1987 Dec 16;149(2):378-84. doi: 10.1016/0006-291x(87)90377-9.
Interactions between C1q and other subunits of C1 were analyzed by sucrose gradient ultracentrifugation. A zone of dilute, radioiodine labelled C1q was sedimented through uniform concentrations of either C1r2C1s2, C1r2, C1r2 or C1s(2). The dissociation constants were found to be 3 x 10(-9) M and 6 x 10(-9) M for C1r2C1s2 and C1r2 binding respectively. Hill coefficients of 1 indicated no cooperativity in these bindings. Positive cooperativity was found in binding of C1s to C1q. Dissociation constants of 2 x 10(-6) M and 5 x 10(-8) M were obtained form computer modelling of a two step binding mechanism. No interaction was detected between C1q and activated C1r2. The data indicate that most of the interactions between C1q and C1r2C1s2 originates from a strong binding to the C1r2 moiety of the zymogen complex. This interaction is lost upon activation of C1r2.
通过蔗糖梯度超速离心分析了C1q与C1其他亚基之间的相互作用。将一个稀释的、放射性碘标记的C1q区域通过均匀浓度的C1r2C1s2、C1r2、C1r2或C1s(2)进行沉降。发现C1r2C1s2和C1r2结合的解离常数分别为3×10(-9) M和6×10(-9) M。希尔系数为1表明这些结合中不存在协同性。在C1s与C1q的结合中发现了正协同性。通过两步结合机制的计算机建模得到的解离常数为2×10(-6) M和5×10(-8) M。未检测到C1q与活化的C1r2之间的相互作用。数据表明，C1q与C1r2C1s2之间的大多数相互作用源于与酶原复合物的C1r2部分的强结合。这种相互作用在C1r2活化后丧失。
