This is an enzyme that acts in the alpha-ketoglutarate pathway, an intermediate pathway in the Krebs cycle in which amino acid derivatives enter the cycle. Alpha ketoglutarate dehydrogenase serves to convert NADH + succinyl-CoA + CO2 into alpha-ketoglutarate + CoA + NAD+.
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.