hydroxyprolinei

Hydroxyproline is a non-standard amino acid, a variation of the standard amino acid proline. It is also known as 3-Hydroxyproline. Hydroxyproline is not coded for by any codon and its presence in a protein sequence must be the result of post-translational modification.

In proteins, hydroxyproline can impart stability to protein structures such as collagen, by creating hydrogen bonds that help to stabilize the protein's triple helix conformation. This is beneficial to the strength and structural integrity of skin, hair, and bone tissue, for example.

Hydroxyproline is only found in collagen type I, a major component of the interstitial tissue in mammals, which includes tendons, ligaments, and skin. This polymer of hydroxyproline and other amino acids is highly stable and is responsible for the strength of many biological tissues.

In the body, hydroxyproline must be synthesized from proline via the enzyme prolyl hydroxylase. This enzyme adds oxygen to a proline residue in a protein structure, producing hydroxyproline.

Hydroxyproline can also be used as a marker of bone turnover. The urine excretion of hydroxyproline is a measure of the amount of bone resorption that has occurred. This can be measured by collecting a sample of urine and running a test to measure the amount of hydroxyproline that it contains.

Because hydroxyproline is a marker of bone turnover, a normal range for its urine excretion is useful in assessing the level of bone disease that is present. A low value could indicate a low rate of bone turnover, suggesting an underactive osteoclasts, while a high value suggests high turnover.