Radical enzymes in anaerobes.
This review describes enzymes that contain radicals and/or catalyze reactions with radical intermediates. Because radicals irreversibly react with dioxygen, most of these enzymes occur in anaerobic bacteria and archaea. Exceptions are the families of coenzyme B(12)- and S-adenosylmethionine (SAM)-dependent radical enzymes, of which some members also occur in aerobes. Especially oxygen-sensitive radical enzymes are the glycyl radical enzymes and 2-hydroxyacyl-CoA dehydratases. The latter are activated by an ATP-dependent one-electron transfer and act via a ketyl radical anion mechanism. Related enzymes are the ATP-dependent benzoyl-CoA reductase and the ATP-independent 4-hydroxybenzoyl-CoA reductase. Ketyl radical anions may also be generated by one-electron oxidation as shown by the flavin-adenine-dinucleotide (FAD)- and [4Fe-4S]-containing 4-hydroxybutyryl-CoA dehydratase. Finally, two radical enzymes are discussed, pyruvate:ferredoxin oxidoreductase and methane-forming methyl-CoM reductase, which catalyze their main reaction in two-electron steps, but subsequent electron transfers proceed via radicals.
Buckel
Wolfgang
W
Fachbereich Biologie, Philipps-Universität, D-35032 Marburg, Germany. buckel@staff.uni-marburg.de
Golding
Bernard T
BT
D000596:Amino Acids / Q000378:metabolism; D001421:Bacteria, Anaerobic / Q000201:enzymology*; D003038:Cobamides / Q000502:physiology*; D005415:Flavins / Q000378:metabolism; D005609:Free Radicals / Q000378:metabolism*; D005998:Glycine / Q000378:metabolism*; D006836:Hydro-Lyases / Q000502:physiology; D008697:Methane / Q000096:biosynthesis; D050743:Pyruvate Synthase / Q000502:physiology; D012436:S-Adenosylmethionine / Q000378:metabolism*
D000596:Amino Acids; D003038:Cobamides; D005415:Flavins; D005609:Free Radicals; D012436:S-Adenosylmethionine; D050743:Pyruvate Synthase; D006836:Hydro-Lyases; C000913:cobamamide; D008697:Methane; D005998:Glycine