title: Stoichiometry and sedimentation properties of the complex formed between the C1q and C1r2C1s2 subcomponents of the first component of complement.
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.
mesh_terms: D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D003166:Complement Activating Enzymes; D003172:Complement C1 / Q000145:classification*; D015922:Complement C1q; D006461:Hemolysis; D006801:Humans; D046911:Macromolecular Substances; D008433:Mathematics; D008970:Molecular Weight; D011817:Rabbits; D012756:Sheep; D014461:Ultracentrifugation
chemical_list: D003172:Complement C1; D046911:Macromolecular Substances; D015922:Complement C1q; D003166:Complement Activating Enzymes