Reversible inactivation of α-ketoglutarate dehydrogenase in response to alterations in the mitochondrial glutathione status

In a previous study, we found that treatment of rat heart mitochondria with H2O2 resulted in a decline and subsequent recovery in the rate of state 3 NADH-linked respiration. These effects were shown to be mediated by reversible alterations in NAD(P)H utilization and in the activities of specific Krebs cycle enzymes alpha-ketoglutarate dehydrogenase (KGDH) and succinate dehydrogenase. The purpose of the current study was to examine potential mechanism(s) by which H2O2 reversibly alters KGDH activity. We report here that inactivation is not simply due to direct interaction of H2O2 with KGDH. In addition, incubation of mitochondria with deferroxamine, an iron chelator, or 1,3-dimethyl-2-thiourea, an oxygen radical scavenger, prior to addition of H2O2 did not alter the rate or extent of inactivation. Thus, inactivation does not appear to involve a more potent oxygen radical formed upon metal-catalyzed oxidation. Inactive KGDH from H2O2-treated mitochondria was reactivated with dithiothreitol, implicating oxidation of a protein sulfhydryl(s). However, the thioredoxin system had no effect, indicating that enzyme inactivation is not due to the formation of intra- or intermolecular disulfide(s) or a sulfenic acid. Upon incubation of mitochondria with H2O2, reduced GSH levels fell rapidly prior to enzyme inactivation but recovered at the same time as enzyme activity. Importantly, treatment of inactive KGDH with glutaredoxin facilitated the GSH-dependent recovery of KGDH activity. Glutaredoxin is characterized as a specific and efficient catalyst of protein deglutathionylation. Thus, the results of the current study indicate that KGDH activity appears to be modulated through enzymatic glutathionylation and deglutathionylation. These studies demonstrate a novel mechanism by which KGDH activity and mitochondrial function can be modulated by redox status.