Type II collagen is specific for cartilaginous tissues. It is essential for the normal embryonic development of the skeleton, for linear growth and for the ability of cartilage to resist compressive forces. Homotrimers of alpha 1(II) chains. Contains mostly 4-hydroxyproline. Prolines at the third position of the tripeptide repeating unit (G-X-P) are 4-hydroxylated in some or all of the chains. Contains 3-hydroxyproline at a few sites. This modification occurs on the first proline residue in the sequence motif Gly-Pro-Hyp, where Hyp is 4-hydroxyproline. These protein fragments were extracted from 160,000 to 600,000 year old bones. The tryptic peptides required multiple purification steps in order to eliminate contaminants and to increase the concentration of peptidic material. Belongs to the fibrillar collagen family.