Translations:Citric acid cycle/10/en

Steps

There are ten basic steps in the citric acid cycle, as outlined below. The cycle is continuously supplied with new carbon in the form of acetyl-CoA, entering at step 0 in the table.

	Reaction type	Substrates	Enzyme	Products	Comment
0 / 10	Aldol condensation	Oxaloacetate + Acetyl CoA + H2O	Citrate synthase	Citrate + CoA-SH	irreversible, extends the 4C oxaloacetate to a 6C molecule
1	Dehydration	Citrate	Aconitase	cis-Aconitate + H2O	reversible isomerisation
2	Hydration	cis-Aconitate + H2O		Isocitrate
3	Oxidation	Isocitrate + NAD+	Isocitrate dehydrogenase	Oxalosuccinate + NADH + H +	generates NADH (equivalent of 2.5 ATP)
4	Decarboxylation	Oxalosuccinate		α-Ketoglutarate + CO2	rate-limiting, irreversible stage, generates a 5C molecule
5	Oxidative decarboxylation	α-Ketoglutarate + NAD+ + CoA-SH	α-Ketoglutarate dehydrogenase, Thiamine pyrophosphate, Lipoic acid, Mg++,transsuccinytase	Succinyl-CoA + NADH + H + + CO2	irreversible stage, generates NADH (equivalent of 2.5 ATP), regenerates the 4C chain (CoA excluded)
6	substrate-level phosphorylation	Succinyl-CoA + GDP + Pi	Succinyl-CoA synthetase	Succinate + CoA-SH + GTP	or ADP→ATP instead of GDP→GTP, generates 1 ATP or equivalent. Condensation reaction of GDP + Pi and hydrolysis of succinyl-CoA involve the H2O needed for balanced equation.
7	Oxidation	Succinate + ubiquinone (Q)	Succinate dehydrogenase	Fumarate + ubiquinol (QH2)	uses FAD as a prosthetic group (FAD→FADH2 in the first step of the reaction) in the enzyme. These two electrons are later transferred to QH2 during Complex II of the ETC, where they generate the equivalent of 1.5 ATP
8	Hydration	Fumarate + H2O	Fumarase	L-Malate	Hydration of C-C double bond
9	Oxidation	L-Malate + NAD+	Malate dehydrogenase	Oxaloacetate + NADH + H+	reversible (in fact, equilibrium favors malate), generates NADH (equivalent of 2.5 ATP)
10 / 0	Aldol condensation	Oxaloacetate + Acetyl CoA + H2O	Citrate synthase	Citrate + CoA-SH	This is the same as step 0 and restarts the cycle. The reaction is irreversible and extends the 4C oxaloacetate to a 6C molecule