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.

Contents

1 Properties 1.1 Nomenclature and classification 1.2 Metabolic pathways 1.3 Kinetic properties 2 Citric acid cycle 2.1 Reaction 2.2 Regulation 3 References

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 (http://ca.expasy.org/cgi-bin/nicezyme.pl?1.2.4.2)
• CAS: 9031-02-1

Metabolic pathways

This enzyme participates in three different pathways:

• Citric acid cycle (KEGG link: MAP00020 (http://www.genome.jp/kegg/pathway/map/map00720.html))
• Lysine degradation (KEGG link: MAP00310 (http://www.genome.jp/kegg/pathway/map/map00310.html))
• Tryptophan metabolism (KEGG link: MAP00380 (http://www.genome.jp/kegg/pathway/map/map00380.html))

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 (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=10848975)