Complement Component 1, Q Subcomponent A (C1qA)

Reid (1974) reported a partial amino acid sequence of 95 residues of the 191 residues in the oxidized A chain of human subcomponent C1q. This region of the A chain contains a repeating sequence of glycine-X-Y, where X is often proline and Y is often hydroxyproline, for 78 residues. The 5 hydroxylysine residues and 5 hydroxyproline residues in the oxidized A chain are all in these 78 residues and only in the Y position of the repeating sequence.Prolonged collagenase digestion of the oxidized A chain yielded a large, apparently C-terminal peptide containing most of the noncollagenous sequences present in the chain. Reid (1974) concluded that the A chain of C1q contains a collagen-like region that constitutes most of the N-terminal half of the chain.