Stewart J L, Sodetz J M
Biochemistry. 1985 Aug 13;24(17):4598-602. doi: 10.1021/bi00338a018.
The basis for the physical association between C8 and C9 in solution was examined by isolating the noncovalently associated alpha-gamma and beta subunits of C8 and determining their respective affinities for C9. Results indicate that only alpha-gamma associates with C9 and this association, though reversible, is complete at near equimolar ratios of each component. Further experiments using purified alpha or gamma revealed that only alpha was capable of forming a stable complex with C9. Although the strength of this interaction was dependent on salt concentration, association was observed in buffer of physiological ionic strength and in human serum. These results establish that the domain on C8 responsible for interaction with C9 is located entirely within alpha. In related experiments, addition of beta to performed dimers of either (alpha-gamma + C9) or (alpha + C9) resulted in complete association of this subunit. These particular results indicate that there are two physically distinct sites on alpha that separately mediate association of alpha with beta and with C9. Furthermore, occupation of one site does not impair interaction at the other.
通过分离C8非共价结合的α-γ和β亚基并测定它们各自与C9的亲和力，研究了溶液中C8和C9之间物理缔合的基础。结果表明，只有α-γ与C9缔合，并且这种缔合虽然是可逆的，但在各组分接近等摩尔比时是完全的。使用纯化的α或γ进行的进一步实验表明，只有α能够与C9形成稳定的复合物。尽管这种相互作用的强度取决于盐浓度，但在生理离子强度的缓冲液和人血清中均观察到缔合。这些结果表明，C8上负责与C9相互作用的结构域完全位于α内。在相关实验中，向预先形成的（α-γ + C9）或（α + C9）二聚体中添加β会导致该亚基完全缔合。这些特定结果表明，α上有两个物理上不同的位点，分别介导α与β以及与C9的缔合。此外，占据一个位点不会损害另一个位点的相互作用。
