carbon fixation reductive tricarboxylic acid cycle https://github.com/geneontology/go-ontology/issues/28429 https://github.com/geneontology/go-ontology/issues/28527 reductive citric acid pathway GO:0019644 biological_process GO:0019643 MetaCyc:P42-PWY reductive carboxylic acid cycle reductive carboxylate cycle MetaCyc:P23-PWY MetaCyc:PWY-5392 reductive TCA cycle reductive Kreb's cycle A pathway leading to the fixation of two molecules of CO2 and the production of one molecule of acetyl-CoA; essentially the oxidative TCA cycle running in reverse. Acetyl-CoA is reductively carboxylated to pyruvate, from which all other central metabolites can be formed. Most of the enzymes of reductive and oxidative TCA cycle are shared, with the exception of three key enzymes that allow the cycle to run in reverse: ATP citrate lyase, 2-oxoglutarate:ferredoxin oxidoreductase, and fumarate reductase. 2-oxoglutarate:ferredoxin oxidoreductase catalyzes the carboxylation of succinyl-CoA to 2-oxoglutarate, ATP citrate lyase the ATP-dependent cleavage of citrate to acetyl-CoA and oxaloacetate, and fumarate reductase the reduction of fumarate forming succinate.