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Medientyp:
E-Artikel
Titel:
Generation of Reactive Oxygen Species in the Reaction Catalyzed by α-Ketoglutarate Dehydrogenase
Beteiligte:
Tretter, Laszlo;
Adam-Vizi, Vera
Erschienen:
Society for Neuroscience, 2004
Erschienen in:The Journal of Neuroscience
Sprache:
Englisch
DOI:
10.1523/jneurosci.1842-04.2004
ISSN:
0270-6474;
1529-2401
Entstehung:
Anmerkungen:
Beschreibung:
<jats:p>α-Ketoglutarate dehydrogenase (α-KGDH), a key enzyme in the Krebs' cycle, is a crucial early target of oxidative stress (Tretter and Adam-Vizi, 2000). The present study demonstrates that α-KGDH is able to generate H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>and, thus, could also be a source of reactive oxygen species (ROS) in mitochondria. Isolated α-KGDH with coenzyme A (HS-CoA) and thiamine pyrophosphate started to produce H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>after addition of α-ketoglutarate in the absence of nicotinamide adenine dinucleotide-oxidized (NAD<jats:sup>+</jats:sup>). NAD<jats:sup>+</jats:sup>, which proved to be a powerful inhibitor of α-KGDH-mediated H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>formation, switched the H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>forming mode of the enzyme to the catalytic [nicotinamide adenine dinucleotide-reduced (NADH) forming] mode. In contrast, NADH stimulated H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>formation by α-KGDH, and for this, neither α-ketoglutarate nor HS-CoA were required. When all of the substrates and cofactors of the enzyme were present, the NADH/NAD<jats:sup>+</jats:sup>ratio determined the rate of H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>production. The higher the NADH/NAD<jats:sup>+</jats:sup>ratio the higher the rate of H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>production. H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>production as well as the catalytic function of the enzyme was activated by Ca<jats:sup>2+</jats:sup>. In synaptosomes, using α-ketoglutarate as respiratory substrate, the rate of H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>production increased by 2.5-fold, and aconitase activity decreased, indicating that α-KGDH can generate H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>in<jats:italic>in situ</jats:italic>mitochondria. Given the NADH/NAD<jats:sup>+</jats:sup>ratio as a key regulator of H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>production by α-KGDH, it is suggested that production of ROS could be significant not only in the respiratory chain but also in the Krebs' cycle when oxidation of NADH is impaired. Thus α-KGDH is not only a target of ROS but could significantly contribute to generation of oxidative stress in the mitochondria.</jats:p>