Methionine, sulfur-containing amino acid obtained by the hydrolysis of a lot of typical proteins. Initially isolated from casein (1922 ), methionine accounts for about 5 percent of the weight of egg albumin; other proteins consist of much smaller sized amounts of methionine. It is among several so-called vital amino acids for mammals and fowl; i.e., they can not manufacture it. In microorganisms it is manufactured from the amino acids cysteine and aspartic acid.

Methionine is essential in methylation (the process by which methyl, or -ch3, groups are added to compounds) and is likewise a precursor of 2 other amino acids, cystine and cysteine. [1]

Other names

Methionine; methionine, l-; γ-methylthio-α-aminobutyric acid; butanoic acid, 2-amino-4-( methylthio)-, (s)-; cymethion; l-(-)- methionine; fulfilled; s-methionine; 2-amino-4-( methylthio) butyric acid; butyric acid, 2-amino-4-( methylthio)-; l(-)- amino-γ-methylthiobutyric acid; l-α-amino-γ-methylmercaptobutyric acid; l-γ-methylthio-α-aminobutyric acid; 2-amino-4-methylthiobutanoic acid; liquimeth; acimethin; l-2-amino-4-( methylthio) butyric acid; (s) -2- amino-4-( methylthio) butanoic acid; h-met-oh; l-homocysteine, s-methyl-; nsc 22946; 2-amino-4-methylthiobutanoic acid (s)-. [2]


Methionine is an amino acid. Amino acids are the foundation that our bodies utilize to make proteins. Methionine is discovered in meat, fish, and dairy products. It plays an important function in the many functions within the body.

Methionine is commonly taken by mouth to deal with liver conditions and viral infections along with lots of other usages. But there is minimal clinical research that supports these uses. [3]


L-methionine, the principal sulfur-containing amino acid in proteins, plays vital functions in cell physiology as an antioxidant and in the breakdown of fats and heavy metals. Previous studies recommending making use of l-methionine as a treatment for depression and other diseases suggest that it might likewise enhance memory and propose a role in brain function. Nevertheless, some proof indicates that an excess of methionine can be damaging and can increase the risk of developing type-2 diabetes, heart problem, particular kinds of cancer, brain modifications such as schizophrenia, and memory problems. [4]


As an important amino acid, methionine is not synthesized de novo in human beings and other animals, which must consume methionine or methionine-containing proteins. In plants and microorganisms, methionine biosynthesis belongs to the aspartate household, together with threonine and lysine (via diaminopimelate, however not via α-aminoadipate). The primary foundation is originated from aspartic acid, while the sulfur might originate from cysteine, methanethiol, or hydrogen sulfide.

First, aspartic acid is transformed through β-aspartyl-semialdehyde into homoserine by two decrease actions of the terminal carboxyl group (homoserine has therefore a γ-hydroxyl, thus the homo- series). The intermediate aspartate-semialdehyde is the branching point with the lysine biosynthetic pathway, where it is instead condensed with pyruvate. Homoserine is the branching point with the threonine pathway, where instead it is isomerised after triggering the terminal hydroxyl with phosphate (also utilized for methionine biosynthesis in plants).

Homoserine is then triggered with a phosphate, succinyl or an acetyl group on the hydroxyl.

In plants and perhaps in some bacteria, phosphate is used. This step is shared with threonine biosynthesis.

In the majority of organisms, an acetyl group is utilized to activate the homoserine. This can be catalysed in germs by an enzyme encoded by metx or meta (not homologues). In enterobacteria and a restricted variety of other organisms, succinate is used. The enzyme that catalyses the reaction is meta and the specificity for acetyl-coa and succinyl-coa is determined by a single residue. The physiological basis for the preference of acetyl-coa or succinyl-coa is unidentified, however such alternative routes are present in some other pathways (e.g. Lysine biosynthesis and arginine biosynthesis).

The hydroxyl activating group is then changed with cysteine, methanethiol, or hydrogen sulfide. A replacement response is technically a γ-elimination followed by a version of a michael addition. All the enzymes included are homologues and members of the cys/met metabolism plp-dependent enzyme household, which is a subset of the plp-dependent fold type i clade. They use the cofactor plp (pyridoxal phosphate), which functions by stabilising carbanion intermediates.

If it responds with cysteine, it produces cystathionine, which is cleaved to yield homocysteine. The enzymes included are cystathionine-γ-synthase (encoded by metb in bacteria) and cystathionine-β-lyase (metc). Cystathionine is bound in a different way in the two enzymes allowing β or γ responses to occur. If it responds with complimentary hydrogen sulfide, it produces homocysteine. This is catalysed by o-acetylhomoserine aminocarboxypropyltransferase (formerly known as o-acetylhomoserine (thiol)- lyase. It is encoded by either mety or metz in germs. If it reacts with methanethiol, it produces methionine straight. Methanethiol is a by-product of catabolic path of specific compounds, for that reason this route is more unusual. If homocysteine is produced, the thiol group is methylated, yielding methionine. Two methionine synthases are understood; one is cobalamin (vitamin b12) reliant and one is independent.

The path using cysteine is called the “transsulfuration path”, while the pathway utilizing hydrogen sulfide (or methanethiol) is called “direct-sulfurylation pathway”.

Cysteine is similarly produced, specifically it can be made from a triggered serine and either from homocysteine (” reverse trans-sulfurylation route”) or from hydrogen sulfide (” direct sulfurylation route”); the triggered serine is generally o-acetyl-serine (by means of cysk or cysm in e. Coli), but in aeropyrum pernix and some other archaea o-phosphoserine is used. Cysk and cysm are homologues, but belong to the plp fold type iii clade. [5]

System of action

The system of the possible anti-hepatotoxic activity of l-methionine is not totally clear. It is thought that metabolism of high dosages of acetaminophen in the liver lead to reduced levels of hepatic glutathione and increased oxidative stress. L-methionine is a precursor to l-cysteine. L-cysteine itself may have antioxidant activity. L-cysteine is likewise a precursor to the antioxidant glutathione. Antioxidant activity of l-methionine and metabolites of l-methionine appear to account for its possible anti-hepatotoxic activity. Current research suggests that methionine itself has free-radical scavenging activity by virtue of its sulfur, as well as its chelating capability. [6]

Dietary sources

The met-content of proteins varies significantly depending upon the food source. Foods with a particularly high portion include eggs (31 mg/g protein), cod (30 mg/g), and chicken (28 mg/g). Intermediate content is in beef (26 mg/g), pork (26 mg/g), milk (25 mg/g), and rice (24 mg/g). Grains and other plant-derived protein sources tend to consist of a lower portion. Examples are corn (21 mg/g), wheat and oats (18 mg/g), rye and beans (15 mg/g), and cauliflower (14 mg/g). Cooking foods at high temperatures (browning) can reduce fulfilled bioavailability due to oxidation (dworschak, 1980).

Given that satisfied can not be synthesized in the body, adequate amounts have to be provided. Met and cys are carefully linked metabolically, and recommendations are frequently given for the amount of both sulfur amino acids (saa), therefore. Healthy adults must get at least 13 mg/kg per day in mix. [7]

What is methionine utilized for?

The sulfur in methionine provides the body with numerous prospective health advantages.

these may include:.

  • Nourishing the hair, skin, and nails
  • Safeguarding the cells from toxins
  • Assisting in the cleansing procedure
  • Slowing down the aging process
  • Helping with the absorption of other nutrients (such as selenium and zinc)
  • Helping in the excretion of heavy metals (such as lead and mercury) assisting the body’s excretion process
  • Preventing excess fat buildup in the liver (by serving as a lipotropic representative– one that helps with the breakdown of fats)
  • Reducing cholesterol levels by increasing lecithin production in the liver

Tylenol (acetaminophen) overdose

Taking an oral (by mouth) dose of methionine within 10 hours of tylenol (acetaminophen) overdose has been used in dealing with acetaminophen poisoning.2 methionine is thought to prevent the byproducts of acetaminophen from harming the liver as a result of an overdose of tylenol. However, other treatments are likewise utilized and methionine might not be the most reliable.


Although a few of the research is blended concerning colon cancer and methionine, a 2013 meta-analysis reports, “this meta-analysis shows that dietary methionine consumption might be associated with reduced risk of colorectal cancer, especially colon cancer. More prospective research studies with long follow-up time are required to validate these findings.” for instance, a 2016 study reported “amongst the 10 essential amino acids tested, methionine deprivation elicited the greatest repressive results on the migration and intrusion of these [breast] cancer cells.”.

Some studies reveal that a low methionine diet could be advantageous. There are specific kinds of cancer cells that depend on methionine to grow. Therefore, limiting the consumption of foods consisting of methionine is beneficial for those who have some types of cancer, since it results in the death of the cancer cells.

Alzheimer’s illness

Research studies recommend that l-methionine may help to enhance memory and brain function, but according to a research study published by molecular neurodegeneration, “some proof suggests that an excess of methionine can be hazardous and can increase the threat of developing type-2 diabetes, cardiovascular disease, certain types of cancer, brain alterations such as schizophrenia, and memory problems.”.

Research study on l-methionine and alzheimer’s disease has actually just been conducted in animal research studies. In a 2015 mouse model research study found that a diet enhanced with l-methionine led to:.

  • An increase in amyloid (a substance that typically develops in the brains of those with alzheimer’s illness)
  • A rise in the level of tau protein in the brain (an increase can lead to tau protein misfolding and clumping together to form abnormal tau tangles, found in those with alzheimer’s)
  • An increase in oxidative stress and inflammatory action (both thought to raise the threat of alzheimer’s illness)
  • Memory impairment and memory loss

The study authors concluded, “taken together, the results of our research study show that an l-methionine-enriched diet causes results in [occurring in a living organism] and might contribute to the appearance of alzheimer’s- like illness in wild-type animals.”.

Other uses

Methionine is commonly taken for other disorders, however there is an absence of scientific research study results to back up the security and effectiveness of its use in these conditions:.

  • Herpes simplex and herpes zoster (shingles)
  • Signs of menopause
  • Swelling of the pancreas
  • Liver issues
  • Anxiety
  • Alcoholism
  • Urinary tract infections (uti’s)
  • Asthma and allergies
  • Schizophrenia [8]

It can produce particles important for typical cell function

Among the major functions of methionine in the body is that it can be used to produce other essential particles.

It is associated with the production of cysteine, the other sulfur-containing amino acid utilized to construct proteins in the body.

Cysteine can, in turn, create a range of particles, consisting of proteins, glutathione and taurine.

Glutathione is in some cases called the “master antioxidant” due to its important function in the defenses of your body.

It likewise contributes in the metabolic process of nutrients in the body and the production of dna and proteins.

Taurine has numerous functions that help keep the health and proper functioning of your cells.

One of the most crucial molecules methionine can be converted into is s-adenosylmethionine, or “sam”.

Sam participates in many different chain reaction by moving part of itself to other particles, consisting of dna and proteins.

Sam is also used in the production of creatine, a crucial molecule for cellular energy.

Overall, methionine is directly or indirectly associated with lots of essential procedures in the body because of the molecules it can end up being.

Methionine can convert into numerous sulfur-containing molecules with important functions, such as glutathione, taurine, sam and creatine. These particles are vital for the typical functions of the cells in your body.

It contributes in DNA methylation

Your dna consists of the information that makes you who you are.

While much of this details may stay the same for your whole life, ecological aspects can really change some aspects of your dna.

This is among the most intriguing functions of methionine– that it can convert into a molecule called sam. Sam can change your dna by including a methyl group (a carbon atom and its connected hydrogen atoms) to it.

The amount of methionine in your diet plan may impact how much of this process takes place, however there are lots of unanswered questions about this.

It is possible that increasing methionine in the diet plan could either increase or decrease how much your dna modifications as a result of sa.

Furthermore, if these modifications happen, they could be beneficial in many cases but detrimental in others.

For instance, some research study has actually revealed that diets greater in nutrients that include methyl groups to your dna may decrease threat of colorectal cancer.

Nevertheless, other research has actually shown that higher methionine consumption might worsen conditions like schizophrenia, maybe due to including more methyl groups to dna.

One of the particles produced by methionine, sam, can change your dna. It isn’t totally clear how the methionine content of your diet plan affects this process, and it is possible that this process is useful in many cases and destructive in others. [9]

Methionine metabolism disorders

There are numerous conditions of methionine and sulfur metabolism in addition to lots of other amino acid and natural acid metabolism conditions.

Homocysteine is an intermediate in methionine metabolic process; it is either remethylated to regenerate methionine or combined with serine in a series of transsulfuration responses to form cystathionine and after that cysteine. Cysteine is then metabolized to sulfite, taurine, and glutathione. Numerous problems in remethylation or transsulfuration can cause homocysteine to accumulate, resulting in disease.

The initial step in methionine metabolism is its conversion to adenosylmethionine; this conversion requires the enzyme methionine adenosyltransferase. Deficiency of this enzyme leads to methionine elevation, which is not scientifically considerable except that it triggers false-positive neonatal screening results for homocystinuria.

Timeless homocystinuria

This condition is triggered by an autosomal recessive deficiency of cystathionine beta-synthase, which catalyzes cystathionine formation from homocysteine and serine. Homocysteine accumulates and dimerizes to form the disulfide homocystine, which is excreted in the urine. Because remethylation is undamaged, some of the additional homocysteine is transformed to methionine, which collects in the blood. Excess homocysteine inclines to thrombosis and has adverse impacts on connective tissue (maybe including fibrillin), especially the eyes and skeleton; adverse neurologic results might be due to apoplexy or a direct effect.

Arterial and venous thromboembolic phenomena can happen at any age. Numerous clients develop ectopia lentis (lens subluxation), intellectual impairment, and osteoporosis. Clients can have a marfanoid habitus although they are not generally tall.

Diagnosis of traditional homocystinuria is by neonatal screening for elevated serum methionine; elevated overall plasma homocysteine levels and/or dna testing are confirmatory. Enzymatic assay in skin fibroblasts can also be done.

Treatment of timeless homocystinuria is a low-methionine diet and l-cysteine supplementation integrated with high-dose pyridoxine (a cystathionine synthetase cofactor) 100 to 500 mg orally once a day. Due to the fact that about half of patients react to high-dose pyridoxine alone, some clinicians do not limit methionine consumption in these patients. Betaine (trimethylglycine), which enhances remethylation, can also help lower homocysteine. Betaine dosage is generally begun at 100 to 125 mg/kg orally 2 times a day and titrated based upon homocysteine levels; requirements differ extensively, often ≥ 9 g/day is required. Folate 1 to 5 mg orally once a day is also offered. With early treatment, intellectual outcome is typical or near typical. Vitamin c, 100 mg orally once a day, may likewise be offered to assist prevent thromboembolism.

Other forms of homocystinuria

Different flaws in the remethylation process can lead to homocystinuria. Problems consist of shortages of methionine synthase (ms) and ms reductase (msr), shipment of methylcobalamin and adenosylcobalamin, and deficiency of methylenetetrahydrofolate reductase (mthfr, which is required to create the 5-methyltetrahydrofolate required for the ms reaction). Since there is no methionine elevation in these forms of homocystinuria, they are not detected by neonatal screening.

Medical manifestations resemble other kinds of homocystinuria. In addition, ms and msr deficiencies are accompanied by neurologic deficits and megaloblastic anemia. Medical manifestation of mthfr deficiency varies, including intellectual disability, psychosis, weakness, ataxia, and spasticity.

Medical diagnosis of ms and msr shortages is suggested by homocystinuria and megaloblastic anemia and verified by dna screening. Patients with cobalamin defects have megaloblastic anemia and methylmalonic acidemia. Mthfr deficiency is detected by dna testing.

Treatment is by replacement of hydroxycobalamin 1 mg im once a day (for patients with ms, msr, and cobalamin problems) and folate in supplements similar to characteristic homocystinuria.


This condition is brought on by shortage of cystathionase, which converts cystathionine to cysteine. Cystathionine build-up leads to increased urinary excretion however no clinical signs.

Sulfite oxidase shortage

Sulfite oxidase converts sulfite to sulfate in the last action of cysteine and methionine destruction; it needs a molybdenum cofactor. Shortage of either the enzyme or the cofactor triggers comparable disease; inheritance for both is autosomal recessive.

In its most serious form, clinical symptoms appear in neonates and include seizures, hypotonia, and myoclonus, progressing to early death. Clients with milder forms may present similarly to cerebral palsy and might have choreiform motions.

Diagnosis of sulfite oxidase deficiency is suggested by raised urinary sulfite and validated by determining enzyme levels in fibroblasts and cofactor levels in liver biopsy specimens and/or genetic testing. Treatment of sulfite oxidase shortage is supportive. [10]


The following doses have actually been studied in scientific research study:.

By mouth

For acetaminophen (tylenol) poisoning: 2.5 grams of methionine every 4 hours for 4 dosages to prevent liver damage and death. Methionine should be offered within 10 hours of taking the acetaminophen. This must be done by a healthcare specialist. [11]

Methionine in the body

The estimated average requirement of adults for overall sulphur amino acids (methionine and cysteine) is 15 mg per kg bodyweight and day (kg − 1d − 1). Recommendations for methionine consumption are confused by enzyme cofactors and substrates such as vitamin b6, vitamin b9 (folate), vitamin b12, choline, betaine, and creatine. These nutrients enable efficient use of methionine– eg, they decrease the need for the body to transform methionine into cysteine. Therefore, although dietary methionine is important for homoeostasis in adults and for normal growth and development in kids, dietary cysteine can reduce the everyday methionine requirements.30 this result is often referred to as the sparing result of cysteine on methionine requirement., the required minimum requirement for methionine consumption in grownups can be around 6 mg kg − 1d − 1.

The body maintains a balance in between synthesis and degradation of protein, and deterioration of amino acids to acquire energy for the body’s requirements. In particular, the liver is important for the body’s protein turnover. The liver’s regulative functions consist of the synthesis of non-essential amino acids, conversion of glucogenic amino acids to glucose or ketogenic amino acids to lipids, conversion of ammonia into urea, and the synthesis of a lot of plasma proteins. A nutritionally sufficient diet plan can be ensured by consuming a large range of protein (10– 35% of total energy intake for adults and 5– 10 % for kids). Protein consumption of 0 · 66 g kg − 1d − 1 of balanced protein suffices for a typical adult. Usually, human beings have around 150 g protein per kg of bodyweight.35 whole-body protein turnover in people is relatively rapid, with a typical protein synthesis rate approximated at around 4 g protein kg − 1d − 1 in the lack of net development. The typical half-life of the overall protein in people is most likely on the order of 80 days. We also assume that body methionine readily equilibrates for the most part with dietary intake, however long-lived proteins and tissues do exist. Presuming an uniform turnover of methionine with first order kinetics, it would be expected that within 2 years more than 80% of methionine in the body is renewed with methionine used up from the diet plan (offered a methionine intake or loss of 10 mg kg − 1d − 1, and a methionine swimming pool of 4 g/kg). [12]

Negative effects

To evaluate the body’s responses to methionine, researchers will provide a single big dose of this amino acid and observe the effects.

This dose is far larger than the advised intake, often around 45 mg/lb (100 mg/kg), or 6.8 grams for someone who weighs 150 pounds (68 kilograms).

This kind of test has actually been carried out over 6,000 times, with mostly small adverse effects. These minor negative effects include dizziness, sleepiness and changes in blood pressure.

One major negative event occurred throughout among these tests, which resulted in the death of an individual with hypertension however good health otherwise.

However, it promises that an accidental overdose of around 70 times the recommended consumption caused the complications.

Overall, it appears that methionine is not especially harmful in healthy human beings, except at incredibly high dosages that would be essentially difficult to acquire through the diet plan.

Although methionine is associated with the production of homocysteine, there is no proof that intake within a normal variety threatens for heart health.


People following lots of types of diet plans will often exceed the suggested minimum consumption of methionine. Side effects in response to big dosages are frequently minor however could become dangerous at very high dosages. [13]


Although methionine was identified as being the most harmful amino acid in relation to growth in animals, the evidence in people does not indicate major toxicity, except at very high levels of intake. In spite of the function of methionine as a precursor of homocysteine, and the role of homocysteine in vascular damage and heart disease, there is no evidence that dietary intake of methionine within sensible limitations will cause cardiovascular damage. A single dosage of 100 mg/kg body weight has actually been shown to be safe, however this dosage is about 7 times the everyday requirement for sulfur amino acids, and duplicated intake for 1 wk was shown to lead to increased homocysteine levels. Daily doses of 250 mg (i.e., 4 mg/kg each day) are just 25% of the everyday requirement and have actually been revealed to be safe. Overall, the literature recommends that the single dosage which is normally given up the methionine packing test (100mg/kg/d) does not trigger any serious problems, except in the extreme case when a 10-fold excess of methionine appears to have been offered, and in clients who have schizophrenia or innate errors of sulfur amino acid metabolism, such as hypermethioninemia. [14]


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