The α-ketoglutarate dehydrogenase complex (KGDHc) represents a rate-limiting step in the Krebs cycle catalyzing the oxidative decarboxylation of α-ketoglutarate while generating succinyl-CoA and NADH. The KGDHc is one of the major generators of oxidative stress in the mitochondrion under pathological conditions; malfunctioning of and reactive oxygen species (ROS) generation by KGDHc are implicated in the progression of senescence/aging, neurodegenerative diseases (such as Alzheimer’s and Parkinson’s diseases), ischemia-reperfusion, hypoxia- and glutamate-induced cerebral damage, infantile lactic acidosis, Friedreich’s ataxia, E3-deficiency (see below), among others. ROS generation by KGDHc is attributed to the homodimeric flavoenzyme E3 component of the complex (dihydrolipoamide dehydrogenase), which is a common component in the pyruvate dehydrogenase complex (PDHc), the branched-chain α-keto acid dehydrogenase complex (BCKDHc) and the glycine cleavage system. Pathogenic mutations of hE3 (h for human) lead to an inherited, often lethal disease known as E3-deficiency; the clinical course of E3-deficiency is greatly diversified and often involves cardiological and/or neurological symptoms. Selected pathogenic mutations of hE3 stimulate the ROS generation by hE3 and hKGDHc or impair the recruitment of hE3 to the harboring complexes, which are likely to be important factors in the respective molecular pathogenesis. To address this, structural alterations of the 14 pathogenic variants of hE3 and their role in the respective molecular pathogenesis have been being investigated in our laboratory by a multifaceted structural approach, which involves circular dichroism and high-field NMR spectroscopies, molecular dynamics simulation, hydrogen/deuterium-exchange mass spectrometry, cryo electron microscopy and (synchrotron) x-ray crystallography. We are also very enthusiastically interested in shedding light on the intimate details of the ROS-generating mechanism of hE3. We also wish to be able to assess the ROS-generating mechanism on the level of the multienzyme complexes that harbor hE3, hence we produce the respective recombinant components for the reconstitution of the hPDHc, hBCKDHc, and hKGDHc.