The benefits and side effects of this essential amino acid.
Amino acids represent one of the bases of metabolism and biological structure . Thanks to them, complex proteins can be formed, which are nothing more than chains of greater or lesser complexity, made from amino acid sequences described in the genetic material of organisms.
Methionine represents one of the essential amino acids for humans , which we are unable to synthesize and must obtain through diet. It has important functions when it comes to forming proteins from nucleic acids, but it also has important effects of its own on the organism, for example by being a key factor in the formation of molecules with sulfur or an important factor in DNA methylation, on which epigenetics depends.
In this article we will review the structure, functions, positive and negative effects, as well as the foods that contain this essential amino acid.
- It may interest you: “Table of the 20 amino acids: types, functions and characteristics”
Biological role of methionine
Methionine is an essential amino acid that is used by our body for the formation of proteins. Unlike other amino acids that can be synthesized in our own body, our body is unable to generate methionine , so it is obtained through food.
The functions of methionine are not limited to the formation of proteins, but it is also the metabolic precursor of several compounds , such as other amino acids such as cysteine or taurine, as well as molecules that interact with DNA, such as S-adenosyl methionine, which has an important role in methylation.
Methionine is a special amino acid, as it is encoded in the AUG codon. This codon indicates not only the placement of a methionine in the polypeptide chain, but it is also the codon that indicates the start of translation . That is, if the ribosome does not detect the AUG codon, the protein will not begin to form.
This does not mean that all the proteins we generate contain methionine, since this amino acid is sometimes discarded by modifications subsequent to the polymerization of the protein.
Effects of methionine on the body
Methionine, as we have mentioned, represents a precursor to various organic substances, including amino acids such as cysteine. Some of the molecules derived from methionine are related to certain physiological effects, both positive and negative .
It is important to mention that most of the observations about the effects of methionine have been made in animal models, such as the fruit fly – Drosophila melanogaster – or the mice – Mus Musculus -, so a greater research effort is required. regarding the effects of this amino acid in humans.
Some of the known effects of methionine on the body are:
1. DNA methylation
Methionine is the precursor of S-adenosyl methionine (SAM), molecules related to the methylation of genetic material. DNA methylations occur when the DNA molecule becomes “adorned” with methyl groups, which has effects on gene expression. That is, it is a form of epigenetic control of DNA .
It has been observed that an excess of methionine in the diet can lead to excess methylation, which is related to carcinogenic and aging processes.
2. Antioxidant
Another of the molecules that derive from methionine is glutathione . This is a molecule with mainly antioxidant functions, that is, it protects us from oxidative damage that can be caused by molecules such as free radicals or other reactive oxygen species.
In addition, glutathione has important functions regulating neurotransmitters such as glutamate or facilitating the excretion of xenobiotics , that is, synthetic molecules that do not belong to the body in which they are found, and can cause damage or metabolic disruption.
3. Effects on cardiovascular health and aging
Another of the by-products of methionine metabolism is homocysteine . Elevated homocysteine levels are linked to poor cardiovascular health , for example by increasing the risk of arteriosclerosis.
The oxidative stress of homocysteine causes damage throughout the body and is also related to an acceleration of the symptoms of aging. An excess of methionine in the diet is related to liver damage and cardiovascular conditions, and it is very likely that it is due to the increase in homocysteine that occurs in the face of too high levels of methionine in the body.
In fact, this relationship has also been tested in the opposite direction. A dietary restriction of methionine reduces oxidative damage at the liver , heart and mitochondrial levels, resulting in a longer life expectancy for animals following these diets.
4. Protection against liver poisoning
One of the main uses of methionine medically is to prevent liver damage caused by an overdose of acetaminophen, commonly known as Paracetamol . Paracetamol, especially if accompanied by high alcohol consumption, has high hepatotoxicity.
Luckily, methionine is useful in reducing the damage caused by acetaminophen overdose, since it helps to break down this molecule and excrete it safely, as long as it is taken within 10 hours of intoxication. The mechanism by which this occurs is still not fully clarified.
5. Source of sulfur
At a biological level, methionine represents one of the largest sources of sulfur available to animals. A sufficient amount of methionine helps improve the health of hair and nails, lower cholesterol through the production of hepatic lecithin, in addition to reducing fat produced in the liver and protecting the kidneys.
What foods contain methionine?
Methionine, as we have seen, is capable of producing serious side effects for health if it is consumed in high quantities. Even so, it is an essential amino acid for life, which must be consumed in a certain amount to avoid causing even more serious problems for the body.
- We recommend: “The 10 foods richest in protein (and amino acids)”
The recommended daily dose of methionine is about 20-30 mg/kg per day , which translates to approximately 1.5-2 grams in a person weighing about 70 kilos. The elderly or people with deficiencies in vitamin B6 and B12 may need to increase their daily methionine intake, which is relatively simple due to the abundance of this amino acid in common foods.
Although the harmful effects of methionine are various, we must remember that these have been observed mainly in animal models . In humans, the doses necessary for these effects to occur are about five times higher than the amount of methionine recommended daily by experts.
Some of the foods richest in methionine are those of animal origin, such as meat, milk or eggs -the latter have 3 grams of methionine per 100g-, but it is also found in abundance in vegetable products such as sesame or soy.
Bibliographic references
- Nimni, M. E., Han, B., & Cordoba, F. (2007). Are we getting enough sulfur in our diet?. Nutrition & metabolism, 4, 24. doi:10.1186/1743-7075-4-24
- Gomez, J., Caro, P., Sanchez, I., Naudi, A., Jove, M., & Portero-Otin, M. et al. (2009). Effect of methionine dietary supplementation on mitochondrial oxygen radical generation and oxidative DNA damage in rat liver and heart. Journal Of Bioenergetics And Biomembranes, 41(3), 309-321. doi:10.1007/s10863-009-9229-3.
- Brosnan, J., & Brosnan, M. (2006). The Sulfur-Containing Amino Acids: An Overview. The Journal Of Nutrition, 136(6), 1636S-1640S. doi:10.1093/jn/136.6.1636s.
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