Methionine

is an α-[|amino acid] with the [|chemical formula] HO2CCH(NH2)CH2CH2SCH3. This [|essential amino acid] is classified as [|nonpolar]. This amino-acid is coded by the codon AUG, also known as the initiation codon, since it indicates mRNA's coding region where translation into protein begins. It is a lipotropic, which is a fat burner or antioxidant. It is critical for the removal of heavy metals (lead or mercury for example) from the body. Methionine also ensures a healthy liver, kidney, bladder and artery functions. It is also used in the maintenance of healthy nails, hair and skin and is also essential for muscle growth and energy. It increases the production of estrogen and can reduce histamine levels. Histamine can cause allergic reactions, dilate blood vessels, and can affect the way the brain sends and receives messages so reducing histamine levels allows proper synaptic function. Since, the human body does not naturally produce methionine, we get it from our food, supplemental pills, or have it administered intravenously in case of illness. We can get methionine from red meat, fish, beans and grains. In supplement form it is often prescribed for the treatment of schizophrenia. Methionine has been shown to be a promising agent in assisting with memory recall and the treatment of other mental disorders such as Parkinson's and Alzheimer's Disease. It is also helpful for people suffering with HIV/AIDs, ADHD (in adults), fibromyalgia, and stress anxiety. It's used to boost protein level for veggitarians and vegans who may not be getting enough protein through their diet. Atheletes, or others who metabolize alot of protein, may also use methionine to boost their protein levels. It is prescribed as a protein replacement for individuals who are considered to be heavy drinkers. Side effects of taking methionine supplements include nausea, vomitting and drowsiness. Deficiencies in methionine levels can lead to severe mental disorders, dementia for example. Other side effects include liver damage, edema, weakness, and brittle hair. In children, low levels of methionine can slow normal growth and development in kids. In pregnant women, insufficient levels may result in neural tube defects in infants, like brain and spinal column disorders such as hydrocephaly or spina bi fida.
 * Methionine**



Biosynthesis
As an essential amino acid, methionine is not synthesized [|de novo] in humans, who must ingest methionine or methionine-containing proteins. In plants and microorganisms, methionine is synthesized via a pathway that uses both [|aspartic acid] and [|cysteine]. First, [|aspartic acid] is converted via β-aspartyl-semialdehyde into homoserine, introducing the pair of contiguous methylene groups. Homoserine converts to //O//-succinyl [|homoserine], which then reacts with cysteine to produce [|cystathionine] , which is cleaved to yield [|homocysteine]. Subsequent methylation of the [|thiol] group by [|folates] affords methionine. Both [|cystathionine-γ-synthase] and [|cystathionine-β-lyase] require [|pyridoxyl-5'-phosphate] as a [|cofactor], whereas [|homocysteine methyltransferase] requires [|vitamin B12] as a cofactor. [|[6]] Enzymes involved in methionine biosynthesis:
 * 1) [|aspartokinase]
 * 2) β-aspartate semialdehyde [|dehydrogenase]
 * 3) homoserine dehydrogenase
 * 4) homoserine O-transsuccinylase
 * 5) cystathionine-γ- [|synthase]
 * 6) cystathionine-β- [|lyase]
 * 7)  [|methionine synthase] (in mammals, this step is performed by [|homocysteine methyltransferase] )

Synthesis
[|Racemic] methionine can be synthesized from diethyl sodium phthalimidomalonate by alkylation with chloroethylmethylsulfide (ClCH2CH2SCH3) followed by hydrolysis and decarboxylation. [|[7]]

Conversion to cysteine
Homocysteine can be converted to cysteine. Methionine is a protein-based amino acid that helps with metabolic function, breaks down fat, and is the primary source of sulfur in the body. Methionine is also critical for the removal of heavy metals, such as lead and mercury, from the body. Some of its other primary purposes include ensuring healthy liver, kidney, bladder, and artery functions; the maintenance of healthy nails, hair, and skin and it is essential for muscle growth and energy. The human body does not naturally produce methionine so it must be ingested in food, or use as a supplemental pill form. Side effects of supplements may include nausea, vomiting, and drowsiness. There aren't negative interactions of methionine with other drugs, but mixing any medication should never be done without doctor's approval. Methionine is found in foods such as red meat, fish, beans, and grains but can also be produced as a supplement.
 * (5) [|Cystathionine-β-synthase] (a PLP-dependent enzyme) combines homocysteine and serine to produce [|cystathionine] . Instead of degrading [|cystathionine] via [|cystathionine-β-lyase], as in the biosynthetic pathway, cystathionine is broken down to [|cysteine] and [|α-ketobutyrate] via (6) [|cystathionine-γ-lyase].
 * (7) The enzyme [|α-ketoacid dehydrogenase] converts α-ketobutyrate to [|propionyl-CoA], which is metabolized to [|succinyl-CoA] in a three-step process (see [|propionyl-CoA] for pathway).