Reverse Krebs cycle

The Reductive/Reverse TCA Cycle (rTCA cycle). Shown are all of the reactants, intermediates and products for this 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 and archaea[1] to produce carbon compounds from carbon dioxide and water by the use of energy-rich reducing agents as electron donors.

The reaction is the citric acid cycle run in reverse. Where the Krebs cycle takes carbohydrates and oxidizes them to CO2 and water, the reverse cycle takes CO2 and H2O to make carbon compounds. This process is used by some bacteria (such as Aquificota) to synthesize carbon compounds, sometimes using hydrogen, sulfide, or thiosulfate as electron donors.[2][3] This process can be seen as an alternative to the fixation of inorganic carbon in the reductive pentose phosphate cycle which occurs in a wide variety of microbes and higher organisms.

  1. ^ Garritano AN, Song W, Thomas T (October 4, 2022). "Carbon fixation pathways across the bacterial and archaeal tree of life". PNAS Nexus. 1 (5) pgac226. doi:10.1093/pnasnexus/pgac226. PMC 9802188. PMID 36712370.
  2. ^ Evans MC, Buchanan BB, Arnon DI (April 1966). "A new ferredoxin-dependent carbon reduction cycle in a photosynthetic bacterium". Proceedings of the National Academy of Sciences of the United States of America. 55 (4): 928–934. Bibcode:1966PNAS...55..928E. doi:10.1073/pnas.55.4.928. PMC 224252. PMID 5219700.
  3. ^ Buchanan BB, Arnon DI (1990). "A reverse KREBS cycle in photosynthesis: consensus at last". Photosynthesis Research. 24: 47–53. doi:10.1007/BF00032643. PMID 11540925. S2CID 2753977.