Molecular weight of the membrane C5b-9 complex of human complement: characterization of the terminal complex as a C5b-9 monomer.

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Abstract
The hydrodynamic properties of the detergent-solubilized, terminal membrane complex of serum [human] complement components C5-C9 [C5b-9(m)] were studied to obtain an estimate of its MW. In a solution of Triton X-100/deoxycholate, the protein complex binds 17% Triton X-100 and 11% deoxycholate by weight. The sedimentation coefficient of the protein-detergent complex is 26 S as determined by sucrose density gradient ultracentrifugation; gel filtration indicated a molecular radius of 11 nm. By EM these hydrodynamic parameters apply to mono-dispersed C5b-9(m) complexes, which were observed as nonaggregated, hollow protein cylinders and were identical to the complement lesions formed on target membranes. The calculated MW of the protein-detergent complex is approximately 1,286,300 to which the protein moiety contributes approximately 1,000,000. The C5b-9(m) complex formed on biological [vertebrate cell] membranes probably is a monomer entity of the C5-C9 complex.