The structure of SAM consists of three components:
1. Adenosine: It comprises a purine base, adenine, attached to a ribose sugar molecule. Adenosine is the nucleoside component of SAM.
2. Methionine: It consists of a sulfur-containing amino acid, methionine, linked to the adenosine moiety. Methionine provides the methyl group that SAM transfers in enzymatic reactions.
3. Sulfonium Linkage: The adenosine and methionine components are connected through a sulfonium linkage. This linkage involves a sulfur atom covalently bonded to the carbon atom of the methionine's methyl group and to the carbon atom of the adenosine moiety's ribose ring.
Here is a simplified structural representation of SAM:
Adenosine—[Sulfonium Linkage]—Methionine
SAM acts as a universal methyl donor in numerous biological processes. It participates in various metabolic reactions, including DNA methylation, protein methylation, and neurotransmitter synthesis. SAM donates its methyl group to specific substrates, leading to the transfer of the methyl group to the target molecule. This process is essential for various cellular functions and plays a crucial role in gene regulation, protein function, and cellular signaling pathways.