Complement Component 9 (C9)

Activation of the complement system results in formation of the membrane attack complex (MAC) on the membranes of target cells. The complex is assembled by sequential addition of 1 molecule each of C5b, C6, C7, and C8 and 6 to 16 molecules of the ninth component, C9.

DiScipio et al. (1984) screened a human liver cDNA library by the colony-hybridization technique using 2 radiolabelled oligonucleotide probes that correspond to known regions of the C9 amino acid sequence. The cDNA coding for C9 was sequenced and the protein sequence--537 amino acids in a single polypeptide chain--was derived. The amino-terminal half of C9 is predominantly hydrophilic and the carboxyl-terminal half is more hydrophobic.