= Complement C9
<Complement C9> is a terminal <complement system> <protein> that can assemble in multiple copies as part of the <membrane attack complex>. Recruitment follows the <C5b>–<complement C6>–<complement C7>–<complement C8> assembly. The repeated copies contribute much of the membrane pore, while the initiating components remain part of the complex.<Structure of complement C6 suggests a mechanism for initiation and unidirectional, sequential assembly of membrane attack complex (MAC) by Alexander E. Aleshin and others>[Introduction: terminal assembly and repeated C9 recruitment]{ref}
A 2016 experiment assembled pores on <liposomes> and checked function through fluorescent-dye release. The complexes were isolated and imaged as frozen-hydrated particles by <cryo-electron microscopy>. The reconstructed complete pore contained18 <complement C9> copies. That experimental end-product count is not a universal threshold for membrane leakage.<Structural basis of complement membrane attack complex formation by Marina Serna and others>[Results: Cryo-EM structure of the MAC; Molecular architecture; Figure1]{ref}
For an original accounting model, suppose ten suitable initiators and126 competent <complement C9> molecules are available, and stipulate18 copies per completed modeled product. The C9 supply permits at most $\lfloor126/18\rfloor=7$ such products. This is a conditional inventory calculation, not a claim that the assay cannot detect leakage from incomplete assemblies.
The experiment links two levels of evidence. A structural reconstruction describes the arrangement of the isolated particles; dye release tests a membrane consequence in the chosen <liposome> preparation. Neither readout alone measures the concentration of freely circulating <complement C9>. Defining the molecular species and the functional endpoint is therefore part of a quantitative interpretation.
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