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Tretter L, Adam-Vizi V: Inhibition of Krebs cycle enzymes by hydrogen peroxide: A key role of [alpha]-ketoglutarate dehydrogenase in limiting NADH production under oxidative stress. J Neurosci. 2000 Dec 15;20(24):8972-9.
In this study we addressed the function of the Krebs cycle to determine which enzyme (s) limits the availability of reduced nicotinamide adenine dinucleotide (NADH) for the respiratory chain under H (2) O (2)-induced oxidative stress, in intact isolated nerve terminals. The enzyme that was most vulnerable to inhibition by H (2) O (2) proved to be aconitase, being completely blocked at 50 microm H (2) O (2). alpha-Ketoglutarate dehydrogenase (alpha-KGDH) was also inhibited but only at higher H (2) O (2) concentrations (>/=100 microm), and only partial inactivation was achieved. The rotenone-induced increase in reduced nicotinamide adenine dinucleotide (phosphate) [NAD (P) H] fluorescence reflecting the amount of NADH available for the respiratory chain was also diminished by H (2) O (2), and the effect exerted at small concentrations ((BCNU), an inhibitor of glutathione reductase. BCNU-insensitive decline by H (2) O (2) in the rotenone-induced NAD (P) H fluorescence correlated with inhibition of alpha-ketoglutarate dehydrogenase. Decrease in the glutamate content of nerve terminals was induced by H (2) O (2) at concentrations inhibiting aconitase. It is concluded that (1) aconitase is the most sensitive enzyme in the Krebs cycle to inhibition by H (2) O (2), (2) at small H (2) O (2) concentrations (aconitase is inactivated, glutamate fuels the Krebs cycle and NADH generation is unaltered, (3) at higher H (2) O (2) concentrations (>/=100 microm) inhibition of alpha-ketoglutarate dehydrogenase limits the amount of NADH available for the respiratory chain, and (4) increased consumption of NADPH makes a contribution to the H (2) O (2)-induced decrease in the amount of reduced pyridine nucleotides. These results emphasize the importance of alpha-KGDH in impaired mitochondrial function under oxidative stress, with implications for neurodegenerative diseases and cell damage induced by ischemia/reperfusion. |
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