Selenocysteine is a naturally occurring amino acid that contains selenium, an essential trace element. It is one of the 21 amino acids that are used by cells to build proteins, but unlike most amino acids, it is not coded for by the standard genetic code. This unique amino acid is synthesized by a specialized machinery, which requires specific sequences and structures in messenger RNA (mRNA) molecules.
Selenocysteine is involved in various biological processes, such as redox regulation, enzyme catalysis, and protein folding. It is a key component of some antioxidant enzymes, such as glutathione peroxidase, which helps protect cells against oxidative stress. It also plays a crucial role in thyroid hormone metabolism, as the enzyme that converts T4 to T3 contains a selenocysteine residue.
Selenocysteine is found in a wide range of proteins in organisms from bacteria to humans. It is particularly abundant in organs that require high levels of antioxidant protection, such as the liver, kidneys, and spleen. Foods that are rich in selenium, such as Brazil nuts, tuna, and sardines, are also good sources of selenocysteine.
The recommended dietary allowance (RDA) for selenium, which is the amount of selenium that is sufficient to meet the needs of most healthy people, is 55 micrograms per day for adults. However, there is no specific RDA for selenocysteine, as it is not a nutrient that is consumed directly.
Selenocysteine deficiency can lead to various health problems, such as increased susceptibility to oxidative stress, thyroid dysfunction, and muscle weakness. In severe cases, it can cause Keshan disease, a type of heart disease that occurs in areas with low selenium intake.
Selenium toxicity is rare, but it can occur if you consume too much selenium through supplements or highly concentrated selenium sources. The tolerable upper intake level (UL) for selenium is 400 micrograms per day for adults, but chronic overconsumption can lead to selenosis, a condition characterized by hair loss, nail brittleness, and neurological symptoms.
Most people can meet their selenium needs through a balanced diet that includes selenium-rich foods. However, some individuals, such as those with gastrointestinal disorders, may have difficulty absorbing selenium from their diet. In such cases, supplements that contain selenium in the form of selenomethionine or selenocysteine can be helpful. However, it is important to consult a healthcare professional before taking any supplements, as excessive selenium intake can be harmful.
The name selenocysteine comes from the Greek word "selene," which means moon, and "cysteine," which is another amino acid.
Selenocysteine was first discovered in 1986, and its unique biosynthesis pathway was elucidated a few years later.
Selenocysteine is only present in a small fraction of all known proteins, but it is highly conserved across species, indicating its important functional role.
This list shows food that are top sources of Selenocysteine and the quantity of Selenocysteine in 100g of food