Collagen is the most abundant protein in the vertebrates. It is present in skin, bones, blood vessels, and corneas. Collagen is composed of three left-handed polypeptide helices as shown in Figure 3.17 are twisted around each other to form right-handed super helix. The amino acid composition of collagen is different. Glycine constitutes one-third of amino acid residues. Proline and 4-hydroxy proline accounts for 30% of amino acid residues. A small amount of 3-hydroxy proline and 5-hydroxy lysine also contributes to the structure of collagen. Triplets of sequence Gly—x—y is repeated in large numbers in a collagen structure, where x and y are mostly proline and hydroxy proline.

Figure 3.17 Diagrammatic Representation of Triple Helix Structure of Collagen