Citric Acid Cycle

Citric Acid Cycle

The Citric Acid Cycle is also known as the Tricarboxylic Acid Cycle (TCA cycle),
the Krebs cycle, or, rarely, the Szent-Györgyi–Krebs cycle.




Citric Acid/Citrate is not Vitamin C. Vitamin C is Ascorbic Acid/Ascorbate.

 

Step/Reaction	Enzyme (Prosthetic Group)
(1) Acetyl CoA + Oxaloacetate + H2O -> Citrate + CoA + H+	Citrate Synthetase
(2) Citrate <=> cis-Aconitate + H2O	Aconitase (Fe-S)
(3) cis-Aconitate + H2O <=> Isocitrate	Aconitase (Fe-S)
(4) Isocitrate + NAD+ <=> α-Ketoglutarate + CO2 + NADH	Isocitrate Dehydrogenase (Lipoic Acid, FAD)
(5) α-Ketoglutarate + NAD+ + CoA <=> Succinyl CoA + CO2 + NADH	α-Ketoglutarate Dehydrogenase Complex (TPP)
(6) Succinyl CoA + Pi + GDP <=> Succinate + GTP + CoA	Succinyl CoA Synthetase
(7) Succinate +FAD (enzyme-bound) <=> Fumarate + FADH2 (enzyme-bound)	Succinate Dehydrogenase (FAD, Fe-S)
(8) Fumarate + H2O <=> L-Malate	Fumarase
(9) L-Malate + NAD+ <=> Oxaloacetate + NADH + H+	Malate Dehydrogenase
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Pyruvate Dehydrogenase Complex of E. Coli

Reaction	Enzyme (Prosthetic Group)
Oxidative Decarboxylation of Pyruvate	Pyruvate Dehydrogenase Component (TPP)
Transfer of the Acetyl Group to CoA	Dihydrolipoyl Transacetylase (Lipoamide)
Regeneration of the Oxidized Form of Lipoamide	Dihydrolipoyl Dehydrogenase (FAD)
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