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

Abstract

The hydrodynamic properties of the detergent-solubilized, terminal membrane complex of serum complement components C5-C9 [C5b-9(m)] were studied to obtain an estimate of its molecular weight. 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, and gel filtration indicated a molecular radius of 11 nm. It was ascertained by electron microscopy that 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 molecular weight of the protein-detergent complex is approximately 1,286,300 to which the protein moiety contributes approximately 1,000,000. The results indicate that the C5b-9(m) complex formed on biological membranes is a monomer entity of the C5-C9 complement components.