Assessing the role of redox carriers in the reduction of CO2 by the oxo-acid: ferredoxin oxidoreductase superfamily.

The oxo-acid:ferredoxin oxidoreductase (OFOR) superfamily of enzymes are responsible for the reversible interconversion of CO2 and oxo-acids, using CoA-derivatives as co-substrates, and requiring redox equivalents in the form of a soluble redox-carrier protein ferredoxin (Fd). Ultimately, these enzymes are responsible for the reduction of CO2 to form pyruvate (in the case of PFOR) and oxo-glutarate (in the case of OGOR), by the reductive carboxylation reaction of acetyl-CoA and succinyl-CoA, respectively. The nature and kind of Fd that is the best redox-carrier to support the reductive reaction has been poorly studied to date. Most organisms that possess an OFOR contain multiple Fd redox-carriers (in addition to flavin-based flavodoxins). Here, we provide a guide for the comparison of various, similar, but non-identical Fd proteins that can interact with the PFOR from Chlorobaculum tepidum, as a model system. The conventional assay is presented, alongside an electrochemically detected assay, which demonstrates the inequivalence of Fd proteins in supporting either component of catalysis.