Collagen also has two uncommon derivative amino acids that are not directly inserted during translation. These amino acids are found at specific locations relative to glycineand are modified post-translationallyby different enzymes, both of which requirevitamin Cas a cofactor.
Hydroxyprolineis derived from prolineand Hydroxylysinederived from lysine. Depending on the type of collagen, varying numbers of hydroxylysinesare glycosylated(mostly having disaccharides attached).