Oxoglutarate dehydrogenase (aka α-ketoglutarate dehydrogenase) is an enzyme most commonly known for its role in the citric acid cycle. Much like pyruvate dehydrogenase, this enzyme forms a complex composed of three components: E₁, E₂ and E₃, which use thiamine pyrophosphate, lipoic acid and FAD as coenzymes, respectively.

Properties

Nomenclature and classification

The official name of this enzyme is oxoglutarate dehydrogenase (OGDC) although it is also commonly known as α-ketoglutarate dehydrogenase (AKGDH).

• EC #: 1.2.4.2
• CAS: 9031-02-1

Metabolic pathways

This enzyme participates in three different pathways:

• Citric acid cycle (KEGG link: MAP00020)
• Lysine degradation (KEGG link: MAP00310)
• Tryptophan metabolism (KEGG link: MAP00380)

Kinetic properties

The following values are from Azotobacter vinelandii ⁽¹⁾:

• K_M: 0.14 ± 0.04 mM
  
• V_max : 9 ± 3 μmol.min^-1.mg^-1

Citric acid cycle

Reaction

The reaction catalyzed by this enzyme in the citric acid cycle is:

α-ketoglutarate + NAD⁺ + CoA → Succinyl CoA + CO₂ + NADH

This reaction proceeds in three steps: decarboxylation of α-ketoglutarate, oxidation and subsequent transfer to CoA, which forms the end product, succinyl CoA. ΔG°' for this reaction is -7.2 kcal mol^-1.

Regulation

Oxoglutarate dehydrogenase is a key control point in the citric acid cycle. It is inhibited by its products, succinyl CoA and NADH. A high energy charge in the cell will also be inhibitive.

References

1. Bunik V, Westphal AH, de Kok A: Kinetic properties of the 2-oxoglutarate dehydrogenase complex from Azotobacter vinelandii evidence for the formation of a precatalytic complex with 2-oxoglutarate. Eur J Biochem 2000; 267(12): 3583-91. Pubmed: 10848975