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Updated: May 31, 2026

Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development
Published on: April 15, 2013
S-Adenosylmethionine-dependent alkylation reactions: when are radical reactions used?
1Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14850, United States. hl379@cornell.edu
Abstract:
S-Adenosylmethionine (SAM) is a versatile small molecule used in many biological reactions. This review focuses on the mechanistic consideration of SAM-dependent methylation and 3-amino-3-carboxypropylation reactions. Special emphasis is given to methylation and 3-amino-3-carboxypropylation of carbon atoms, for which both nucleophilic mechanisms and radical mechanisms are used, depending on the specific enzymatic reactions. What is the logic behind Nature's choice of different reaction mechanisms? Here I aim to rationalize the choice of different reaction mechanisms in SAM-dependent alkylation reaction by analyzing a few enzymatic reactions in depth. These reactions include SAM-dependent cyclopropane fatty acid synthesis, DNA cytosine methylation, RNA adenosine C2 and C8 methylation, and 3-amino-3-carboxypropylation involved in diphthamide biosynthesis and wybutosine biosynthesis.
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