Methionine (amino acid): what it is, what functions it performs, and how to obtain it

Amino acids represent one of the bases of metabolism and biological structure. Thanks to them, complex proteins can be formed, which are no more than chains of greater or lesser complexity, made from sequences of amino acids described in the genetic material of organisms.

Methionine represents one of the essential amino acids for humanswhich we are unable to synthesize and must obtain through diet. It has important functions in forming proteins from nucleic acids, but also has important effects on the body itself, for example as a key factor in the formation of molecules with sulfur or an important factor in the methylation of DNA, on which depends the epigenetics.

In this article we will review the structure, functions, positive and negative effects, as well as the foods that contain this essential amino acid.

Biological role of methionine

Methionine is an essential amino acid that is used by our body for protein formation. Unlike other amino acids that can be synthesized in our own body, our organism is incapable of generating methionineso he gets it from the feed.

The functions of the methionine are not limited to the formation of proteins, but it is also the metabolic precursor of several compoundsas well as other amino acids such as cysteine or taurine, as well as molecules that interact with DNA, such as S-adenosyl methionine, which plays an important role in methylation.

structure of methionine

During the process of protein formation, the genetic code of the nucleic acids – specifically RNA – is translated into a chain of amino acids that make up the protein. RNA information is read in groups of 3 nucleotides, called codons. Each of these codons indicates the correct amino acid to be sequentially included within the peptide chain.

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 also the placement of a methionine in the polypeptide chain. is the codon that indicates the beginning of the 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, as this amino acid is sometimes discarded by subsequent modifications to the polymerization of the protein.

Effects of methionine on the body

Methionine, as mentioned above, represents a precursor of several 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.

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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 with respect to 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 is “adorned” with methyl groups, which has effects on gene expression. I mean, it’s a form of epigenetic DNA control.

It has been observed that an excess of methionine in the diet can lead to an excess of methylation, which is related to cancerous and aging processes.

2. Antioxidant

Another of the molecules that derive from methionine is the glutathione. This is a molecule with mainly antioxidant functions, i.e. it protects us from oxidative damage 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 xenobioticsthat is, synthetic molecules that do not belong to the body in which they are found, and may cause metabolic damage or disruption.

3. Effects on cardiovascular health and aging

Another of the products derived from the metabolism of methionine is the homocysteine. Elevated homocysteine levels are related to poor health of the cardiovascular systemfor example by increasing the risk of developing arteriosclerosis.

The oxidative stress of homocysteine causes damage to the whole organism and is also related to an acceleration of the symptoms of aging. Excess methionine in the diet is associated with liver damage and cardiovascular disease, most likely due to increased homocysteine in the face of too high levels of methionine in the body.

In fact, this relationship has also been proven in the opposite direction. Dietary restriction of methionine reduces oxidative damage at liver levelThis results in a longer life expectancy for the animals that follow these diets.

4. Protection against liver toxicity

One of the main uses of methionine at the medical level is to prevent liver damage caused by an acetaminophen overdose, commonly known as Paracetamol. Paracetamol, especially if accompanied by high alcohol consumption, has a high hepatotoxicity.

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Luckily, methionine is useful for reducing the damage caused by acetaminophen overdose, because helps degrade this molecule. and to excrete it safely, provided it is taken within 10 hours of poisoning. The mechanism by which this occurs is not yet fully clarified.

5. Source of sulphur

At the biological level, methionine represents one of the largest sources of sulphur 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 the fat that is produced in the liver and protecting the kidneys.

Methionine - Eggs

What foods contain methionine?

Methionine, as we have seen, is capable of producing serious health side effects if consumed in high amounts. Even so, it is an essential amino acid for life, which should be consumed in a certain amount to avoid causing even more serious problems for the body.

The recommended daily dose of methionine is about 20-30 mg/kg per dayThis translates into approximately 1.5 – 2 grams in a person weighing about 70 kilos. Older people or those with vitamin B6 and B12 deficiencies may need to increase their daily methionine intake, which is relatively simple because of the abundance of this amino acid in common foods.

While the harmful effects of methionine are various, we must remember that these have been observed mainly in animal models. In humans, the doses needed for these effects to occur are about five times 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 contain 3 grams of methionine per 100gr – but it is also found in abundance in plant products such as sesame or soybeans.

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.