Reverse Krebs cycle

[2][3] This process can be seen as an alternative to the fixation of inorganic carbon in the Calvin cycle which occurs in a wide variety of microbes and higher organisms.

There are three enzymes specific to the reductive citric acid cycle – citrate lyase, fumarate reductase, and α-ketoglutarate synthase.

It has been found that some non-consecutive steps of the cycle can be catalyzed by minerals through photochemistry,[6] while entire two and three-step sequences can be promoted by metal ions such as iron (as reducing agents) under acidic conditions.

The kinetic and thermodynamic parameters of the reduction of highly oxidized species to push the rTCA cycle are seemingly unlikely without the necessary action of biological catalysts known as enzymes.

[10][11] Many reactions of the reverse Krebs cycle, including thioesterification and hydrolysis, could have been catalyzed by iron-sulfide minerals at deep sea alkaline hydrothermal vent cavities.

[12] More recently, aqueous microdroplets have been shown to promote reductive carboxylation reactions in the reverse Krebs cycle.

[15] Thiomicrospira denitrificans, Candidatus Arcobacter, and Chlorobaculum tepidum have been shown to utilize the rTCA cycle to turn CO2 into carbon compounds.