Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 18, Issue 51, Pages 16463-16472Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201202869
Keywords
bond dissociation energy; enzymes; hydrogen transfer; S-adenosylmethionine; radical reactions
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Funding
- Deutsche Forschungsgemeinschaft [Zi 436/13-1, SFB 749]
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S-Adenosylmethionine (SAM) plays an essential role in a variety of enzyme-mediated radical reactions. One-electron reduction of SAM is currently believed to generate the C5'-desoxyadenosyl radical, which subsequently abstracts a hydrogen atom from the actual substrate in a catalytic or a non-catalytic fashion. Using a combination of theoretical and experimental bond dissociation energy (BDE) data, the energetics of these radical processes have now been quantified. SAM-derived radicals are found to react with their respective substrates in an exothermic fashion in enzymes using SAM in a stoichiometric (non-catalytic) way. In contrast, the catalytic use of SAM appears to be linked to a sequence of moderately endothermic and exothermic reaction steps. The use of SAM in spore photoproduct lyase (SPL) appears to fit neither of these general categories and appears to constitute the first example of a SAM-initiated radical reaction propagated independently of the cofactor.
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