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Methionine, sulfur-containing amino acid obtained by the hydrolysis of many typical proteins. First 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 numerous so-called essential amino acids for mammals and fowl; i.e., they can not manufacture it. In bacteria it is synthesized from the amino acids cysteine and aspartic acid.

Methionine is necessary in methylation (the procedure by which methyl, or -ch3, groups are contributed 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; satisfied; 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 building blocks that our bodies use to make proteins. Methionine is discovered in meat, fish, and dairy products. It plays an essential role in the many functions within the body.

Methionine is commonly taken by mouth to deal with liver disorders and viral infections together with numerous other uses. However there is minimal clinical research study that supports these usages. [3]


L-methionine, the principal sulfur-containing amino acid in proteins, plays vital roles in cell physiology as an antioxidant and in the breakdown of fats and heavy metals. Previous research studies recommending making use of l-methionine as a treatment for depression and other diseases suggest that it may also enhance memory and propose a function in brain function. However, some proof shows that an excess of methionine can be hazardous and can increase the threat of establishing type-2 diabetes, heart problem, specific kinds of cancer, brain alterations such as schizophrenia, and memory disability. [4]


As a necessary amino acid, methionine is not synthesized de novo in human beings and other animals, which should ingest methionine or methionine-containing proteins. In plants and microorganisms, methionine biosynthesis comes from the aspartate household, in addition to threonine and lysine (through diaminopimelate, but not by means of α-aminoadipate). The primary foundation is derived from aspartic acid, while the sulfur may originate from cysteine, methanethiol, or hydrogen sulfide.

Initially, aspartic acid is converted through β-aspartyl-semialdehyde into homoserine by 2 decrease steps of the terminal carboxyl group (homoserine has therefore a γ-hydroxyl, hence the homo- series). The intermediate aspartate-semialdehyde is the branching point with the lysine biosynthetic path, where it is instead condensed with pyruvate. Homoserine is the branching point with the threonine path, where rather it is isomerised after activating the terminal hydroxyl with phosphate (likewise utilized for methionine biosynthesis in plants).

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

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

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

The hydroxyl triggering group is then replaced with cysteine, methanethiol, or hydrogen sulfide. A replacement response is technically a γ-elimination followed by a variation 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 utilise the cofactor plp (pyridoxal phosphate), which works by stabilising carbanion intermediates.

If it responds with cysteine, it produces cystathionine, which is cleaved to yield homocysteine. The enzymes involved 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 permitting β or γ responses to happen. If it responds with free 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 bacteria. If it reacts with methanethiol, it produces methionine straight. Methanethiol is a by-product of catabolic pathway of certain substances, for that reason this path is more unusual. If homocysteine is produced, the thiol group is methylated, yielding methionine. Two methionine synthases are known; one is cobalamin (vitamin b12) reliant and one is independent.

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

Cysteine is likewise produced, namely 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 usually o-acetyl-serine (via cysk or cysm in e. Coli), but in aeropyrum pernix and some other archaea o-phosphoserine is utilized. Cysk and cysm are homologues, however belong to the plp fold type iii clade. [5]

Mechanism of action

The system of the possible anti-hepatotoxic activity of l-methionine is not totally clear. It is believed that metabolic process 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 might 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. Recent research recommends that methionine itself has free-radical scavenging activity by virtue of its sulfur, along with its chelating ability. [6]

Dietary sources

The met-content of proteins varies significantly depending upon the food source. Foods with a particularly high percentage include eggs (31 mg/g protein), cod (30 mg/g), and chicken (28 mg/g). Intermediate content remains 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 heats (browning) can decrease fulfilled bioavailability due to oxidation (dworschak, 1980).

Given that fulfilled can not be synthesized in the body, appropriate amounts have to be supplied. Met and cys are carefully connected metabolically, and suggestions are frequently given for the sum of both sulfur amino acids (saa), for that reason. Healthy grownups need to get at least 13 mg/kg each day in combination. [7]

What is methionine utilized for?

The sulfur in methionine supplies the body with many possible health benefits.

these may consist of:.

  • Nurturing the hair, skin, and nails
  • Protecting the cells from contaminants
  • Facilitating the cleansing process
  • Decreasing the aging procedure
  • Aiding with the absorption of other nutrients (such as selenium and zinc)
  • Assisting in the excretion of heavy metals (such as lead and mercury) assisting the body’s excretion process
  • Avoiding excess fat buildup in the liver (by functioning 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) dosage of methionine within 10 hours of tylenol (acetaminophen) overdose has actually been used in treating acetaminophen poisoning.2 methionine is believed to avoid the by-products of acetaminophen from damaging the liver as a result of an overdose of tylenol. However, other treatments are likewise used and methionine might not be the most reliable.


Although some of the research is blended regarding colon cancer and methionine, a 2013 meta-analysis reports, “this meta-analysis indicates that dietary methionine intake may be related to decreased danger of colorectal cancer, particularly colon cancer. More prospective research studies with long follow-up time are required to validate these findings.” for example, a 2016 research study reported “among the 10 essential amino acids tested, methionine deprivation elicited the strongest inhibitory impacts on the migration and intrusion of these [breast] cancer cells.”.

Some studies show that a low methionine diet could be helpful. There are specific types of cancer cells that depend upon methionine to grow. Hence, restricting the consumption of foods including methionine is useful for those who have some types of cancer, since it results in the death of the cancer cells.

Alzheimer’s illness

Studies recommend that l-methionine might help to improve memory and brain function, however according to a study published by molecular neurodegeneration, “some proof indicates that an excess of methionine can be damaging and can increase the risk of developing type-2 diabetes, cardiovascular disease, certain kinds of cancer, brain modifications such as schizophrenia, and memory problems.”.

Research study on l-methionine and alzheimer’s disease has actually just been carried out in animal studies. In a 2015 mouse design research study discovered that a diet enhanced with l-methionine resulted in:.

  • A boost in amyloid (a substance that frequently builds up in the brains of those with alzheimer’s illness)
  • An increase in the level of tau protein in the brain (a boost can lead to tau protein misfolding and clumping together to form irregular tau tangles, found in those with alzheimer’s)
  • An increase in oxidative tension and inflammatory reaction (both believed to raise the danger of alzheimer’s disease)
  • Memory impairment and amnesia

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

Other usages

Methionine is frequently considered other disorders, but there is an absence of clinical research study results to back up the safety and effectiveness of its usage in these conditions:.

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

It can produce particles critical for typical cell function

One of the significant functions of methionine in the body is that it can be used to produce other crucial particles.

It is involved in the production of cysteine, the other sulfur-containing amino acid used to develop proteins in the body.

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

Glutathione is often called the “master anti-oxidant” due to its crucial role in the defenses of your body.

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

Taurine has lots of functions that help maintain the health and appropriate functioning of your cells.

Among the most important particles methionine can be converted into is s-adenosylmethionine, or “sam”.

Sam participates in several chain reaction by transferring part of itself to other molecules, consisting of dna and proteins.

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

In general, methionine is straight or indirectly associated with numerous essential processes in the body because of the molecules it can become.

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

It plays a role in DNA methylation

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

While much of this details may stay the very same for your entire life, ecological aspects can actually change some elements of your dna.

This is one of the most fascinating functions of methionine– that it can convert into a particle called sam. Sam can alter your dna by adding a methyl group (a carbon atom and its attached hydrogen atoms) to it.

The amount of methionine in your diet plan may impact just how much of this procedure takes place, but there are numerous unanswered questions about this.

It is possible that increasing methionine in the diet might either increase or reduce just how much your dna changes as a result of sa.

Additionally, if these changes happen, they could be beneficial in many cases however destructive in others.

For example, some research study has shown that diets greater in nutrients that add methyl groups to your dna may lower threat of colorectal cancer.

However, other research has actually revealed that greater methionine intake might get worse conditions like schizophrenia, possibly due to adding more methyl groups to dna.

Among the molecules produced by methionine, sam, can change your dna. It isn’t fully clear how the methionine material of your diet affects this process, and it is possible that this process is helpful in many cases and destructive in others. [9]

Methionine metabolism conditions

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

Homocysteine is an intermediate in methionine metabolism; it is either remethylated to restore methionine or integrated with serine in a series of transsulfuration responses to form cystathionine and after that cysteine. Cysteine is then metabolized to sulfite, taurine, and glutathione. Various problems in remethylation or transsulfuration can trigger homocysteine to collect, leading to disease.

The primary step in methionine metabolism is its conversion to adenosylmethionine; this conversion requires the enzyme methionine adenosyltransferase. Shortage of this enzyme results in methionine elevation, which is not scientifically substantial other than that it triggers false-positive neonatal screening results for homocystinuria.

Classic homocystinuria

This condition is triggered by an autosomal recessive deficiency of cystathionine beta-synthase, which catalyzes cystathionine formation from homocysteine and serine. Homocysteine collects and dimerizes to form the disulfide homocystine, which is excreted in the urine. Due to the fact that remethylation is intact, a few of the additional homocysteine is converted to methionine, which collects in the blood. Excess homocysteine predisposes to thrombosis and has unfavorable results on connective tissue (perhaps including fibrillin), particularly the eyes and skeleton; negative neurologic results might be because of apoplexy or a direct effect.

Arterial and venous thromboembolic phenomena can happen at any age. Lots of clients establish ectopia lentis (lens subluxation), intellectual impairment, and osteoporosis. Patients can have a marfanoid habitus despite the fact that they are not typically high.

Medical diagnosis of traditional homocystinuria is by neonatal screening for elevated serum methionine; raised total plasma homocysteine levels and/or dna testing are confirmatory. Enzymatic assay in skin fibroblasts can likewise be done.

Treatment of traditional 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. Because about half of clients respond to high-dose pyridoxine alone, some clinicians do not restrict methionine intake in these patients. Betaine (trimethylglycine), which enhances remethylation, can likewise assist lower homocysteine. Betaine dose is normally begun at 100 to 125 mg/kg orally 2 times a day and titrated based upon homocysteine levels; requirements vary extensively, often ≥ 9 g/day is required. Folate 1 to 5 mg orally once a day is likewise offered. With early treatment, intellectual result is regular or near typical. Vitamin c, 100 mg orally once a day, may also be given to assist avoid thromboembolism.

Other types of homocystinuria

Numerous flaws in the remethylation procedure can result in homocystinuria. Flaws include shortages of methionine synthase (ms) and ms reductase (msr), delivery of methylcobalamin and adenosylcobalamin, and shortage of methylenetetrahydrofolate reductase (mthfr, which is required to produce the 5-methyltetrahydrofolate required for the ms response). Due to the fact that there is no methionine elevation in these forms of homocystinuria, they are not spotted by neonatal screening.

Medical symptoms are similar to other types of homocystinuria. In addition, ms and msr shortages are accompanied by neurologic deficits and megaloblastic anemia. Scientific symptom of mthfr deficiency is variable, consisting of intellectual impairment, psychosis, weakness, ataxia, and spasticity.

Diagnosis of ms and msr deficiencies is suggested by homocystinuria and megaloblastic anemia and verified by dna screening. Clients with cobalamin problems have megaloblastic anemia and methylmalonic acidemia. Mthfr shortage is detected by dna screening.

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


This disorder is brought on by deficiency of cystathionase, which converts cystathionine to cysteine. Cystathionine accumulation results in increased urinary excretion however no medical symptoms.

Sulfite oxidase deficiency

Sulfite oxidase transforms sulfite to sulfate in the last step of cysteine and methionine degradation; it requires a molybdenum cofactor. Shortage of either the enzyme or the cofactor triggers similar disease; inheritance for both is autosomal recessive.

In its most severe form, medical manifestations appear in neonates and consist of seizures, hypotonia, and myoclonus, progressing to early death. Clients with milder kinds may provide similarly to cerebral palsy and might have choreiform movements.

Medical diagnosis of sulfite oxidase shortage is recommended by raised urinary sulfite and verified by measuring enzyme levels in fibroblasts and cofactor levels in liver biopsy specimens and/or genetic screening. Treatment of sulfite oxidase shortage is supportive. [10]


The following dosages 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 given within 10 hours of taking the acetaminophen. This must be done by a healthcare specialist. [11]

Methionine in the human body

The approximated average requirement of adults for overall sulphur amino acids (methionine and cysteine) is 15 mg per kg bodyweight and day (kg − 1d − 1). Suggestions 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 allow efficient use of methionine– eg, they decrease the need for the body to transform methionine into cysteine. Thus, although dietary methionine is important for homoeostasis in grownups and for regular development and advancement in children, dietary cysteine can lower the everyday methionine requirements.30 this effect is typically described as the sparing result of cysteine on methionine requirement., the required minimum requirement for methionine consumption in adults can be around 6 mg kg − 1d − 1.

The human body maintains a balance in between synthesis and deterioration of protein, and deterioration of amino acids to acquire energy for the body’s requirements. In particular, the liver is necessary for the body’s protein turnover. The liver’s regulative functions include 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 many plasma proteins. A nutritionally appropriate diet plan can be made sure by eating a vast array 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 well balanced protein is sufficient for an average adult. Usually, human beings have around 150 g protein per kg of bodyweight.35 whole-body protein turnover in human beings is fairly quick, with an average protein synthesis rate estimated at around 4 g protein kg − 1d − 1 in the lack of net growth. The typical half-life of the overall protein in humans is probably on the order of 80 days. We also presume that body methionine readily equilibrates for the most part with dietary intake, but long-lived proteins and tissues do exist. Presuming a homogeneous turnover of methionine with first order kinetics, it would be expected that within 2 years more than 80% of methionine in the human body is renewed with methionine taken up from the diet plan (offered a methionine consumption or loss of 10 mg kg − 1d − 1, and a methionine pool of 4 g/kg). [12]

Side effects

To assess the body’s responses to methionine, researchers will provide a single large dosage of this amino acid and observe the impacts.

This dose is far larger than the recommended consumption, typically around 45 mg/lb (100 mg/kg), or 6.8 grams for somebody who weighs 150 pounds (68 kilograms).

This kind of test has been performed over 6,000 times, with mainly minor adverse effects. These small adverse effects consist of dizziness, drowsiness and modifications in blood pressure.

One major negative occasion happened throughout one of these tests, which led to the death of a specific with hypertension but good health otherwise.

However, it promises that an unintentional overdose of around 70 times the suggested intake triggered the issues.

Overall, it appears that methionine is not especially harmful in healthy people, except at exceptionally high doses that would be virtually impossible to obtain through the diet plan.

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


Individuals following numerous types of diets will often exceed the suggested minimum intake of methionine. Side effects in action to big doses are frequently minor however could become dangerous at incredibly high dosages. [13]


Although methionine was labeled as being the most toxic amino acid in relation to development in animals, the evidence in human beings does not point to major toxicity, other than at extremely high levels of intake. Regardless of the function of methionine as a precursor of homocysteine, and the function of homocysteine in vascular damage and heart disease, there is no evidence that dietary consumption of methionine within sensible limits will trigger cardiovascular damage. A single dosage of 100 mg/kg body weight has been revealed to be safe, but this dosage has to do with 7 times the day-to-day requirement for sulfur amino acids, and duplicated consumption for 1 wk was revealed to result in increased homocysteine levels. Daily doses of 250 mg (i.e., 4 mg/kg daily) are just 25% of the daily requirement and have actually been revealed to be safe. In general, the literature recommends that the single dosage which is usually given up the methionine filling test (100mg/kg/d) does not cause any serious problems, except in the extreme case when a 10-fold excess of methionine appears to have been provided, and in clients who have schizophrenia or innate mistakes of sulfur amino acid metabolism, such as hypermethioninemia. [14]


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