Article: S-Adenosyl methionine

S-Adenosyl methionine
Chemical name	S-Adenosyl-L-methionine
Other names	S-Adenosyl methionine S-Adenosylmethionine SAM, AdoMet, Adomet
Marketing names	SAMe, SAM-e
Chemical formula	C15H24N6O5S
Molecular mass	400.455 g/mol
CAS number	29908-03-0
Density	x.xxx g/cm3
Melting point	xx.x °C
Boiling point	xx.x °C
SMILES	xxx
Structure
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Biochemistry of S-adenosyl methionine

S-adenosyl methionine (SAM) is an biological compound involved in methyl group transfers, and is present in all living cells.

SAM was first discovered in 1952 (Cantoni). It is synthesized endogenously from adenosine triphosphate (ATP) and methionine by methionine adenosyltransferase EC 2.5.1.6. Transmethylation, transsulfuration and aminopropylation are the metabolic pathways that use SAM. Although these anabolic reactions occur throughout the body, most SAM is produced and consumed in the liver (Cantoni). The activated methyl group (CH₃) in SAM allows donation of this group to an acceptor substrate in transmethylation reactions. More than 40 metabolic reactions involve the transfer of a methyl group of SAM to various substrates such as nucleic acids, proteins and lipids.

SAM cycle

The reactions that produce, consume and regenerate SAM are called the SAM cycle. In the first step of this cycle, the SAM-dependent methylases (EC 2.1.1) that use SAM as a substrate produce S-adenosyl homocysteine as a product. This is hydrolysed to homocysteine and adenosine by S-adenosylhomocysteine hydrolase EC 3.3.1.1 and the homocysteine recycled back to methionine through transfer of a methyl group from 5-methyltetrahydrofolate, by one of the two classes of methionine synthases EC 2.1.1.13 or EC 2.1.1.14. This methionine can then be converted back to SAM, completing the cycle.

Polyamine biosynthesis

Another major role of SAM is in polyamine biosynthesis. Here, SAM is decarboxylated by Adenosylmethionine decarboxylase EC 4.1.1.50 to form S-adenosyl-5'-3-methylpropylamine. This compound then donates its n-propylamine group in the biosynthesis of polyamines such as spermidine and spermine from putrescine.

SAM is required for cellular growth and repair. It is also involved in the biosynthesis of several hormones and neurotransmitters that affect mood, such as epinephrine. Methylases are also responsible for the addition of methyl groups to the 2' hydroxyls of the first and second nucleotides next to the 5' cap in messenger RNA.

Therapeutic uses of SAM

In the United States SAM is sold as a nutritional supplement under the marketing name SAM-e (also spelled SAME or SAMe; pronounced "sam ee"). SAM is also known as Gumbaral, Samyr, Adomet and Admethionine. Some research[1] has shown that taking SAM on a regular basis can help fight depression, liver disease, and the pain of osteoarthritis.

Therapeutic use of SAM has increased as dietary supplements have gained in popularity, especially after the Dietary Supplement Health and Education Act was passed in 1999. This law allowed the distribution of SAM as an over-the-counter supplement, and therefore allowed it to bypass the regulatory requirements of the Food and Drug Administration (FDA). SAM has been suggested to have a therapeutic effect in liver disease, mood disorders and osteoporosis.

Because of structural instability, stable salt forms of SAM are required for its use as an oral drug. Although salt forms have been developed, SAM is still liable to degradation leading to distributors that may advertise a dose higher than what is actually being ingested. A common side effect is gastrointestinal distress and people who have a history of bipolar disorder are also at risk of developing manic symptoms. Therapeutic doses range from 800mg/day to 1600mg/day.

See also

• DNA methyltransferase