Citric Acid Cycle

A Citric Acid Cycle Schematic

The Citric Acid Cycle is a key metabolic pathway that connects carbohydrate, fat, and protein metabolism!!! See also [1].

• Krebs cycle importance
• Krebs cycle overview
• Krebs cycle reactions

The Citric Acid Cycle (tricarboxylic acid cycle) is a series of enzyme catalyzed reactions which are critical in cellular respiration. Under oxidative conditions, pyruvate continues to be metabolized through the tricarboxylic acid cycle. In this cycle, Acetyl-CoA, a byproduct of glycolysis, along with various cofactors, are broken down into carbon dioxide, water, and energy in the form of GTP and NADH.

Pyruvate dehydrogenase

The multienzyme complex together catalyzes five distinct reactions in the conversion of pyruvate to acetyl-CoA. The overall result is described by the following reaction:

Pyruvate + CoA + NAD+ ==> Acetyl-CoA + CO2 + NADH

However, pyruvate dehydrogenase (E1) is responsible for only the first two of the five reactions. The first of these is the decarboxylation of pyruvate and coupling of thiamine pyrophosphate (TPP) to form hydroxyethyl-TPP.

Pyruvate + TPP ==> Hydroxyethyl-TPP + CO2

Step 0 / 10 - Aldol condensation - Citrate synthase

• Citrate Synthase
• Step 0 / 10 = Krebs cycle step 1
• ATP-citrate synthase

Step 1 - Dehydration - Aconitase

• Aconitase
• 1st step of Krebs cycle step 2

Step 2 - Hydration - Aconitase

• Aconitase
• 2nd step of Krebs cycle step 2

Step 3 - Oxidation - Isocitrate dehydrogenase

• Isocitrate dehydrogenase
• 1st step of Krebs cycle step 3

Step 4 - Decarboxylation - Isocitrate dehydrogenase

• Isocitrate dehydrogenase
• 2nd step of Krebs cycle step 3

Step 5 - Oxidative decarboxylation - α-Ketoglutarate dehydrogenase (2-Oxoglutarate Dehydrogenase)

• 2-Oxoglutarate Dehydrogenase
• Step 5 = Krebs cycle step 4

Step 6 - Substrate-level phosphorylation - Succinyl-CoA synthetase

• Succinyl-CoA synthetase
• Step 6 = Krebs cycle step 5

Step 7 - Oxidation - Succinate dehydrogenase

• Succinate Dehydrogenase
• Step 7 = Krebs cycle step 6

Step 8 - Hydration - Fumarase

• Fumarase
• Step 8 = Krebs cycle step 7

Step 9 - Oxidation - Malate dehydrogenase

• Malate dehydrogenase
• Step 9 = Krebs cycle step 8

Articles in Proteopedia concerning Citric Acid Cycle include:

• Citrate Synthase Structure & Mechanism
• Aconitase
• Isocitrate Dehydrogenase
• 2-Oxoglutarate Dehydrogenase (also known as alpha-ketoglutarate dehydrogenase)
• Succinyl-CoA Synthetase
• Succinate Dehydrogenase
• Fumarase
• Malate Dehydrogenase
• Glutamate Dehydrogenase

To view Citric Acid Cycle related proteins which are Structure Index entries see:

• Aconitase

To view automatically seeded indices concerning Citric Acid Cycle See:

• Citric Acid Cycle