Meta-Biol

• Pathways

The mitochondrial alpha-ketoglutarate dehydrogenase complex catalyzes the reaction of alpha-ketoadipate, CoASH, and NAD+ to form glutaryl-CoA, CO2, and NADH. The enzyme complex contains multiple copies of three different proteins, E1 (OGDH), E2 (DLST), and E3 (DLD), each with distinct catalytic activities (Reed and Hackert 1990; Zhou et al 2001). The reaction starts with the oxidative decarboxylation of alpha-ketoadipate catalyzed by E1alpha and beta (alpha ketoglutarate dehydrogenase). Lipoamide cofactor associated with E1 is reduced at the same time. Next, the glutaryl group derived from alpha ketoglutarate is transferred to coenzyme A in two steps catalyzed E2 (dihydrolipolyl transacetylase). Finally, the oxidized form of lipoamide is regenerated and electrons are transferred to NAD+ in two steps catalyzed by E3 (dihydrolipoyl dehydrogenase). The biochemical details of this reaction have been worked out with alpha ketoglutarate dehydrogenase complex and subunits purified from bovine tissue (McCartney et al. 1998). While all of the human proteins are known as predicted protein products of cloned genes, direct experimental evidence for their functions is available only for E3 (DLD) (Brautigam et al. 2005).