S-Adenosylmethionine
Definition and meaning of S-Adenosylmethionine in chemistry.
S-Adenosylmethionine (SAM) is a coenzyme that serves as the universal methyl donor in cells, synthesized from the amino acid methionine and ATP. It carries a highly reactive methyl group attached to its sulfonium sulfur atom and participates in over 100 different biochemical reactions.
In more detail
SAM's methyl group (CH3) is the primary source of methyl groups for cellular methylation reactions. These reactions regulate gene expression, establish epigenetic markers, synthesize neurotransmitters, and produce signaling molecules essential for cell function. SAM is critical in DNA methylation, protein modification, lipid synthesis, and polyamine formation. After donating its methyl group, SAM is converted to S-adenosylhomocysteine, which is hydrolyzed to homocysteine; homocysteine can then be remethylated to methionine and reconverted to SAM, regenerating the active coenzyme.
Key facts
| Chemical formula | C15H22N6O5S |
|---|---|
| Field | Biochemistry |
| Primary role | Universal methyl donor in cells |
| Location | Found in all living organisms |
In DNA methylation, DNA methyltransferase enzymes use SAM to transfer methyl groups to cytosine bases in DNA, creating 5-methylcytosine residues that regulate gene expression and are essential for epigenetic inheritance.
Frequently asked questions
Why is SAM essential for health?
SAM is required for DNA methylation, neurotransmitter synthesis, and immune function; deficiencies are associated with depression, liver disease, and neurological disorders.
How is SAM replenished in cells?
SAM is continuously synthesized from methionine by the enzyme methionine adenosyltransferase (MAT), making dietary methionine intake important for maintaining adequate SAM levels.