Does acetogenesis really require especially low reduction potential?

Area of Science:

• Biochemistry
• Microbiology
• Metabolic Engineering

Background:

• Acetogenesis produces acetate from carbon dioxide, a globally significant metabolic process.
• Traditionally, acetogenesis was thought to require highly negative ferredoxin reduction potentials (≈-500mV).
• This requirement for extreme electron donors is unusual compared to other metabolic pathways.

Purpose of the Study:

• To investigate if acetogenesis necessitates unique cellular conditions or extreme redox potentials.
• To propose an alternative mechanism for acetogenesis that utilizes enzymes with moderate reduction potentials.
• To re-evaluate the thermodynamic requirements for CO2 reduction and acetyl-CoA synthesis in acetogenesis.

Main Methods:

• The study proposes a mechanistic model for the CO-dehydrogenase-acetyl-CoA-synthase complex.
• Analysis of reaction coupling to overcome unfavorable thermodynamics.
• Thermodynamic evaluation of pyruvate synthesis using ferredoxins and CO2.

Main Results:

• The CO-dehydrogenase-acetyl-CoA-synthase complex couples CO2 reduction to CO with acetyl-CoA synthesis.
• This coupling allows acetogenesis to proceed with ferredoxins of moderate reduction potential (≈-400mV).
• Pyruvate synthesis from CO2 and moderate ferredoxins is shown to be an energy-neutral process.

Conclusions:

• Acetogenesis can occur under normal cellular redox conditions, challenging previous assumptions.
• Mechanistic coupling by enzymatic complexes can reduce thermodynamic barriers in metabolic pathways.
• This revised understanding offers insights for metabolic engineering applications.