α-Ketoglutarate dehydrogenase: a mitochondrial redox sensor.
α-Ketoglutarate dehydrogenase (KGDH), a key regulatory enzyme within the Krebs cycle, is sensitive to mitochondrial redox status. Treatment of mitochondria with H₂O₂ results in reversible inhibition of KGDH due to glutathionylation of the cofactor, lipoic acid. Upon consumption of H₂O₂, glutathione is removed by glutaredoxin restoring KGDH activity. Glutathionylation appears to be enzymatically catalysed or require a unique microenvironment. This may represent an antioxidant response, diminishing the flow of electrons to the respiratory chain and protecting sulphydryl residues from oxidative damage. KGDH is, however, also susceptible to oxidative damage. 4-Hydroxy-2-nonenal (HNE), a lipid peroxidation product, reacts with lipoic acid resulting in enzyme inactivation. Evidence indicates that HNE modified lipoic acid is cleaved from KGDH, potentially the first step of a repair process. KGDH is therefore a likely redox sensor, reversibly altering metabolism to reduce oxidative damage and, under severe oxidative stress, acting as a sentinel of mitochondrial viability.
Free Radical Biology and Aging Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA.
Aaron L
AL
McLain
Pamela A
PA
Szweda
Luke I
LI
Szweda
D006801:Humans; D007655:Ketoglutarate Dehydrogenase Complex / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology*; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology; D015398:Signal Transduction
D007655:Ketoglutarate Dehydrogenase Complex