A whole class of AdoMet-dependent metalloenzymes

AdoMet is known to be a potent and highly versatile methylating agent yielding S-adenosylhomocysteine as the co-product [55]. Its function as a source of putative 

5 -deoxyadenosyl radicals described here is rather unusual. However, a few other biological systems are known to use AdoMet for a similar function, even though again in no case was direct evidence for an intermediate 5 -deoxyadenosyl radical provided. These systems are the pyruvate formate lyase (PFL), biotin synthase (BS) and lysine 2,3 aminomutase (LAM). The following points concerning these systems are the most notable. 

the flexibility of the iron-sulfur center gives it the potential to exist under different [2Fe-2S], [3Fe-4S], [4Fe-4S] forms. Whether this has functional importance remains to be determined. Very recently the Fnr protein, the pyruvate formate lyase and the biotin synthase were shown to share this property [48-50]. Second, its reducing power allows it to inject electrons into protein-bound AdoMet, as a prerequisite for the formation of an essential glycyl radical. Third, this radical is used for ribose activation, by hydrogen atom abstraction. It is likely that this reaction is mediated by a cysteinyl radical [53]. Fourth, formate is used as the hydrogen donor for ribose reduction [38]. 

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