Reverse Krebs cycle

The reverse Krebs cycle (also known as the reverse tricarboxylic acid cycle, the reverse TCA cycle, or the reverse citric acid cycle, or the reductive tricarboxylic acid cycle, or the reductive TCA cycle) is a sequence of chemical reactions that are used by some bacteria to produce carbon compounds from carbon dioxide and water by the use of energy-rich reducing agents as electron donors. See also [1], [2], and Carbon Fixation.

The cycle involves the biosynthesis of from two molecules of CO2. The key steps of the reverse Krebs cycle are:

• to , using NADH + H+

Oxaloacetate + NADH/H+ -> Malate + NAD+

• to , catalyzed by an oxidoreductase, Fumarate reductase (e.g. 1d4c).

Fumarate + FADH2 <=> Succinate + FAD

• Succinate to , an ATP dependent step

Succinate + ATP + CoA -> Succinyl-CoA + ADP + Pi

• to , using NADPH + H+ and another molecule of CO2

α-Ketoglutarate + CO2 + NAD(P)H/H+ -> Isocitrate + NAD(P)+

• converted into and acetyl-CoA, this is an ATP dependent step and the key enzyme is the ATP citrate lyase.

Citrate + ATP + CoA -> Oxaloacetate + Acetyl-CoA + ADP + Pi

This pathway is cyclic due to the regeneration of the oxaloacetate.