Hydroxyproline (HYP) is a non-essential amino acid that is derived from another amino acid, proline. It is created by the interaction of ascorbic acid, also known as vitamin C, and proline. This causes a hydroxyl group, which is a bonded oxygen-hydrogen molecule, to attach itself to the carbon atom of the proline acid, changing it into hydroxyproline.
In 1902, this amino acid was isolated in gelatin. It is a proteinogenic amino acid, which means that it is one of 22 amino acids that are an integral part of the human body's proteins, and is also a part of the standard human genetic code. The production of hydroxyproline takes place in the gastrointestinal tract.
Without vitamin C, the production of this amino acid is impossible. This is a serious problem, as without it, the body is unable to manufacture its most important structural protein, collagen. Both proline and hydroxyproline are essential in the formation of this key substance, and a lack of either one can lead to serious collagen instability in the body.
A deficiency of this amino acid is often one of the first visible signs of scurvy. The ultimate cause of scurvy is too little vitamin C, but this will first manifest itself as a collagen deficiency, due to the poor production of hydroxyproline. Without it, any collagen in the body becomes unstable and is often expelled in the urine. The lack of the collagen protein causes easy bruising of the skin, breakdowns in connective tissue, and possibly internal bleeding. Other issues caused by limited amounts of this amino acid include hair loss and receding gums.
Aside from collagen, the only mammalian protein that is created using hydroxyproline is elastin. As its name implies, this protein has elastic qualities, and is responsible for allowing skin to retain its shape. It is also stored, in mammals, at sites on the body where a great deal of weight is borne, or where there are large transfers of mechanical energy. This allows the body to endure movement and pressure without significant deformity. A lack of it makes this protein harder to create, but the results are not as dramatic or immediate as when collagen is not being produced.
There is no need for humans to have a dietary source for this amino acid. Its precursor, proline, is also a non-essential amino acid and is produced in the body. Vitamin C, however, is an essential nutrient for the human body, and must be consumed — most often from fruits and vegetables — for the body to function properly.