From: Ribonucleotide reduction - horizontal transfer of a required function spans all three domains
 | Class I* | Class II | Class III |
---|---|---|---|
Operation | Aerobic | O2 independent, B12 dependent | Anaerobic SAM dependent |
Structure | α2β2 | α or α2 | α2, activated by β2 |
Component names | α:NrdA or NrdE β: NrdB or NrdF | NrdJ | Enzyme proper: NrdD Activase: NrdG |
Radical generating metal site | Fe-O-Fe | Co (in AdoCbl) | β: 4Fe-4S and AdoMet |
Distribution | Common in bacteria universal in eukaryotes, rare in archaea | Common in bacteria and archaea, rare in eukaryotes | Common in bacteria and archaea, rare in eukaryotes |