C5 is synthesised in the liver as a single polypeptide chain. Before secretion the molecule is glycosylated and secreted into plasma as a 190kDa glycoprotein consisting of a disulphide linked alpha-chain (115kDa) and beta-chain (75kDa). C5 precursor is first processed by the removal of 4 basic residues, forming two chains, beta and alpha, linked by a disulfide bond. C5 convertase activates C5 by cleaving the alpha chain, releasing C5a anaphylatoxin and generating C5b (beta chain + alpha chain).
