Hughes-Jones N C, Gardner B
Immunology. 1978 Mar;34(3):459-63.
The strength of the bond between 125I-labelled C1q and immune complexes, Fc piece, dextran sulphate, polyglutamic acid and polylysine has been investigated. The binding of C1q to Fc piece, small molecular weight (less than 10,000) dextran sulphate, polyglutamic acid and polylysine have value; for the functional affinity constant (Ko) in the range of 0.2-1.5 X 10(4) M-1. In contrast the binding of C1q to immune complexes and large molecular weight polyions (greater than 100,000 is much greater and lies in the range 3 X 10(7)--4 X 10(8) M-1. The differences in the binding constants between the two groups can be explained if the Fc piece and small molecular weight compounds bind to only 1 head of the C1q molecule but the immune complexes and large molecules bind to 2 heads. There are probably 6 binding sites on the C1q molecule for dextran sulphate. The enhancement of the binding affinity of C1q by reduction in ionic strength and the reaction with polyions, indicate that ionic groups are present near or within the binding sites.
对¹²⁵I标记的C1q与免疫复合物、Fc片段、硫酸葡聚糖、聚谷氨酸和聚赖氨酸之间的结合强度进行了研究。C1q与Fc片段、小分子量（小于10,000）硫酸葡聚糖、聚谷氨酸和聚赖氨酸的结合具有一定价值；其功能亲和常数（Ko）在0.2 - 1.5×10⁴ M⁻¹范围内。相比之下，C1q与免疫复合物和大分子聚离子（大于100,000）的结合要强得多，其范围在3×10⁷ - 4×10⁸ M⁻¹之间。如果Fc片段和小分子量化合物仅与C1q分子的一个头部结合，而免疫复合物和大分子与两个头部结合，那么这两组之间结合常数的差异就可以得到解释。C1q分子上可能有6个与硫酸葡聚糖结合的位点。离子强度降低以及与聚离子反应导致C1q结合亲和力增强，这表明结合位点附近或内部存在离子基团。
