5-Adenosylmethionine nucleophilic substitution reaction

Nucleophilic substitution reactions are important in biological systems as well. The most common reaction involves nucleophilic substitution at the CH3 group in 5-adenosylmethionine, or SAM. SAM is the cell s equivalent of CH3I. 

This reaction is a nucleophilic substitution reaction. The nucleophilic atom is the sulfur atom of methionine. The leaving group is the weakly basic triphosphate group of ATP. The product, S-adenosylmethionine, contains a methyl-sulfonium... 

S-Adenosylmethionine then acts as the substrate for other nucleophilic substitution reactions. In the biosynthesis of choline, for example, it transfers its methyl group to a nucleophilic nitrogen atom of 2-(N,N-dimethylamino)ethanol ... 

FIGURE 16.7 Nucleophilic substitution at the primary carbon of adenosine triphosphate (ATP) by the sulfur atom of methionine yields S-adenosylmethionine (SAM). The reaction is catalyzed by an enzyme. 

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