Collagen type IX is a minor cartilage non-fibrillar collagen. It is associated with type II collagen fibrils. Trimers composed of three different chains: alpha 1(IX), alpha 2(IX), and alpha 3(IX). Prolines at the third position of the tripeptide repeating unit (G-X-Y) are hydroxylated in some or all of the chains. Belongs to the fibril-associated collagens with interrupted helices (FACIT) family.