Radical enzymes in anaerobes

Area of Science:

• Biochemistry
• Enzymology
• Radical Chemistry

Background:

• Radical enzymes catalyze reactions involving radical intermediates.
• Most radical enzymes are found in anaerobic bacteria and archaea due to oxygen sensitivity.
• Exceptions include coenzyme B12- and S-adenosylmethionine (SAM)-dependent radical enzymes, some of which are present in aerobes.

Purpose of the Study:

• To review enzymes that contain radicals or catalyze reactions with radical intermediates.
• To highlight the occurrence and mechanisms of various radical enzyme families.
• To discuss the role of oxygen sensitivity in the distribution of these enzymes.

Main Methods:

• Literature review of radical enzyme research.
• Classification of radical enzymes based on cofactors and reaction mechanisms.
• Discussion of oxygen sensitivity and activation mechanisms.

Main Results:

• Identified oxygen-sensitive radical enzymes like glycyl radical enzymes and 2-hydroxyacyl-CoA dehydratases.
• Described ATP-dependent activation and ketyl radical anion mechanisms for some enzymes.
• Highlighted flavin-adenine-dinucleotide (FAD)- and [4Fe-4S]-containing enzymes and their radical intermediates.
• Discussed pyruvate:ferredoxin oxidoreductase and methane-forming methyl-CoM reductase involving radical electron transfers.

Conclusions:

• Radical enzymes are diverse and play crucial roles in various metabolic pathways.
• Oxygen sensitivity significantly influences the prevalence of radical enzymes in different environments.
• Understanding radical enzyme mechanisms provides insights into biological electron transfer processes.