An amino acid derived from proline (one of the twenty amino acids used to make proteins) which is found in gelatin and collagen. It has the chemical formula C5H9NO3. Hydroxyproline helps stabilize the collagen molecule. The making of hydroxyproline by the body is dependent on the presence of vitamin C; if there is not enough vitamin C in the body and not enough hydroxyproline is made, the collagen fibers weaken. This results in the skin lesions which are a part of scurvy (a disease caused by a deficiency of vitamin C).