PMID: 6975324Dec 1, 1981Paper

Stoichiometry and sedimentation properties of the complex formed between the C1q and C1r2C1s2 subcomponents of the first component of complement

The Journal of Immunology : Official Journal of the American Association of Immunologists
R C SiegelP H Poon

Abstract

We have examined the functional and hydrodynamic properties of the first component of human complement, C1, and the activated first component, C1-, reassembled in the presence of Ca++ from C1q and either the C1r2C1s2 or the C1r-2C1s-2 tetramer. Reconstituted C1 has hemolytic activity similar to C1 in serum. As long as either tetramer is in excess and the total concentration is low, we find that only a 1:1 complex is formed between C1q and either the unactivated or activated tetramer. This complex sediments at 15.9 +/- 0.2 Svedbergs and has a complex sediments at 15.9 +/- 0.2 Svedbergs and has a m.w. of 739,000 +/- 37,000. The boundary shape of the sedimenting C1- preparation was broader than that of C1 suggesting the association constant between C1r2C1s2 and C1q may have decreased upon activation. At elevated concentrations, with more than a molar excess of C1q, C1 aggregated to form both 16S and 23S species.

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