Methionine is an essential amino acid that helps initiate the translation of messenger RNA by being the first amino acid incorporated into the N-terminal position of all proteins. It is also a source of sulfur, which the body requires for normal metabolism and growth. Methionine helps break down fats, detoxify lead and other heavy metals, diminish muscle weakness, and prevent brittle hair. Methionine reacts with adenosine triphosphate (ATP) to synthesize many vital substances, including epinephrine and choline.
The measurement of methionine, along with 23 other amino acids, is included in the Amino Acids in Plasma and the Amino Acids in Urine tests.
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Methionine (Met/M) is an aliphatic, sulfur-containing, essential amino acid and a precursor of succinyl-CoA, homocysteine, cysteine, creatine, and carnitine. Recent research has demonstrated that methionine can regulate mammals' metabolic processes, innate immune systems, and digestive functioning. It also intervenes in lipid metabolism, activation of endogenous antioxidant enzymes, and glutathione biosynthesis to counteract oxidative stress. In addition, methionine restriction prevents altered methionine/ transmethylation metabolism, thereby decreasing DNA damage and carcinogenic processes and possibly preventing arterial, neuropsychiatric, and neurodegenerative diseases.
S-adenosyl-l-methionine (SAM or SAMe) is a compound formed from a reaction of methionine and adenosine triphosphate (ATP). It is the main methyl donor in the human body and is involved in various biochemical pathways.
Methionine adenosyltransferase converts methionine to SAM. SAM then serves as a methyl donor in many methyltransferase reactions and is converted to S-adenosylhomocysteine (SAH). Adenosylhomocysteinase converts SAH to homocysteine.
There are two fates of homocysteine.
- Methionine can be regenerated from homocysteine via methionine synthase. It can also be remethylated using glycine betaine to methionine via the enzyme Betaine-homocysteine methyltransferase (BHMT).
- Homocysteine can be converted to cysteine. Cystathionine-β-synthase combines homocysteine and serine to produce cystathionine.
Methionine and its derivatives fulfill many vital functions in the body.
Source of sulfur: Methionine is an essential source of sulfur for numerous compounds, such as the amino acids cysteine and taurine. The body uses sulfur for healthy hair, skin, and nail growth, to increase the liver's production of lecithin, reduce liver fat, protect the kidneys, excrete heavy metals, and regulate the formation of ammonia in the urine.
S-adenosyl-l-methionine (SAM) reactions: SAM, a derivative of methionine, is involved in synthesizing epinephrine, choline, and other substances and is a significant methyl donor.
Lipotropic: Methionine is lipotropic, helping to prevent fat accumulation in the liver and typically aiding the detoxification of metabolic wastes and toxins.
Paracetamol overdose treatment: Methionine is used in the treatment of paracetamol poisoning to prevent liver damage.
Arthritis treatment: SAM relieves arthritis and has fewer side effects than common anti-inflammatory drugs like ibuprofen and aspirin.
Depression: SAM is prescribed more than any antidepressant and is considered adequate, quick-acting, and with fewer side effects. It may boost the activity of essential brain chemicals involved in mood, such as norepinephrine, dopamine, and serotonin.
Liver function: Methionine levels determine the liver’s concentration of sulfur-containing compounds, and SAM improves and normalizes liver function. It is also used to treat cirrhosis and alcohol damage and is key to the production of glutathione. SAM also inactivates estrogens to prevent suppressed bile flow in pregnant women or those on oral contraceptives.
Neurological disorders: SAM is considered to improve the binding of neurotransmitters to receptor sites in the brain and the regeneration of neuron axons following injury.
Methionine also plays a role in the synthesis of phosphatidylcholine and other phospholipids. Improper conversion of methionine can lead to atherosclerosis.
While virtually all protein-containing foods have some methionine, the amount varies widely. Eggs, fish, and meats contain high amounts of this amino acid. It is estimated that around 8% of the amino acids in egg whites are sulfur-containing amino acids (methionine and cysteine). Plant proteins usually have even lower quantities of these amino acids.
Despite the low intake among vegetarians, research has shown that they have higher blood concentrations of methionine than those who eat meat and fish. This finding led the researchers to conclude that dietary content and blood concentrations of methionine are not always directly related.
Although methionine has essential roles in the body, some research shows the benefits of low diets in this amino acid. Some cancer cells are dependent on dietary methionine to grow. In these cases, limiting your dietary intake could help starve cancer cells. Since plant proteins are often lower in methionine than animal proteins, some researchers believe that plant-based diets could be a tool to fight some cancers. Additionally, several studies in animals show that reducing methionine can increase lifespan and improve health.
