Proline is an amino acid that is necessary for the functioning of the human body. It is produced by glutamate, also known as glutamic acid. With the proper diet, both glutamate and, therefore, proline are produced naturally by humans. This means that proline is a non-essential amino acid, because people do not require an outside source.
This amino acid was first found in the compound casein in 1901, and its discovery is credited to Hermann Emil Fischer, a German chemist. It occurs naturally as colorless crystals, and is soluble in water. Unlike most other amino acids, it is also soluble in alcohol. It is also one of only two amino acids — the other being glycine — that does not follow what is known as the Ramachandran Plot. This describes several typical angles which occur in the structure of amino acids, in a protein structure. Both it and glycine have angles that do not conform to the plot.
Proline is key in maintaining healthy skin as well as its underlying connective tissue. Both it and lysine are essential in the formation of collagen, a substance which cushions joints and helps to heal cartilage. This amino acid is also assists in breaking down proteins in the body, which allows the formation of new cells.
In addition, this amino acid is necessary for proper muscle tissue maintenance. Endurance runners and competitive bodybuilders often experience a lack of proline, which can lead to a decrease in muscle tissue. Without a sufficient source of glutamic acid, the precursor to proline, the body will consume its own muscle tissue for energy, limiting or completely negating any muscle gains from exercise.
The most common natural sources of this compound are meat and dairy products, as they contain high levels of glutamate. A person consuming limited amounts of protein, or on a strict vegetarian diet, is at risk of deficiency and should consider a supplement. Proline supplements are most commonly found as part of combination amino acid formulas.
One of the most common medical uses of this acid is to treat a serious tissue injury, as additional proline in the body promotes skin regrowth and elasticity. It is also used in treatments for back pain and arthritis, owing to its joint-cushioning effects. The daily recommended dosage for this amino acid is between 500 and 1,000 milligrams (mg). Research has also shown an increase in effectiveness when it is combined with vitamin C.