3-Nitropropionate, the toxic substance of Indigofera , is a suicide inactivator of succinate dehydrogenase

Abstract

We have shown that 3-nitropropionate, an isoelectronic analogue of succinate, is a suicide inactivator of succinate dehydrogenase [succinate:(acceptor) However, the precise mechanism of inactivation, as well as mechanistic extrapolations to the oxidation of succinate, must await the elucidation of the structure of the modified enzyme. We can now explain the toxicity of plants such as Indigofera endecaphylla for mammals and fowl as being due to the irreversible blockage of the Krebs cycle by 3-nitropropionate carbanion.Nitroalkanes are good substrates for the flavoenzymes D-amino acid oxidase, glucose oxidase, and L-amino acid oxidase (1-5). The nitroalkane carbanions are many orders of magnitude more reactive than their conjugate carbon acids and, in one case (6), even more reactive than the best physiological substrates (e.g., nitroethane anion compared to glucose with glucose oxidase). Most importantly, and in contrast to any physiological substrate, the chemical mechanism of the enzymic oxidation of nitroalkanes is understood in great detail. For D-amino acid oxidase and nitroethane, it was shown (2) that the substrate carbanion attacks the flavin at N-5 in the rate-determining step to form a covalent adduct (pathway 1 in Eq. 1) from which nitrite is eliminated rapidly to form a highly reactive N-5 iminium adduct. In the normal catalytic cycle (pathway 2 in Eq. 1) the iminium is rapidly hydrated to form an N-5 carbinolamine from which reduced flavin is also rapidly eliminated to form the product acetaldehyde. However, the pivotal N-5 iminium intermediate, as would be expected, is highly reactive with a variety of nucleophiles in addition to H20 (2, 5). Those having unbonded electron pairs (such as NH3, NH20H, and mercap- Second, it occurred to us that, in contrast to D-amino acid oxidase and nitroethane (2)

The impact of mitochondrial energetic dysfunction on apoptosis in outer hair cells of the cochlea following exposure to intense noise

“…This approach has been widely used in previous studies of both in vitro and in vivo subjects to generate an experimental model of mitochondrial dysfunction (Alston et al, 1977;Coles et al, 1979;Ludolph et al, 1992). Studies have shown that the resulting level of ATP suppression following a 3-NP treatment is dose-and timedependent.…”

“…However, whether the mitochondrial energy production is a crucial factor that controls the cell's decision to die by apoptosis or necrosis is not known, nor is the role of mitochondrial energy production in regulating the apoptotic process, once the process is initiated. To address these issues, we used an established model of mitochondrial dysfunction induced by local application of 3-nitropropionic acid (3-NP), an irreversible inhibitor of succinate dehydrogenase (SDH), to produce mitochondrial dysfunction (Alston et al, 1977;Coles et al, 1979;Ludolph et al, 1992), and investigated the effects of the mitochondrial energetic deficiency on the generation of apoptosis and necrosis following exposure to intense noise. Specifically, the following questions were addressed: In the noise-damaged cochlea, did reduction of the mitochondrial energy production: (1) prevent the induction of apoptosis; (2) shift OHC death from apoptosis to necrosis; (3) disrupt the execution of the apoptotic process?…”

Mechanisms of Cell Death Induced by the Mitochondrial Toxin 3-Nitropropionic Acid: Acute Excitotoxic Necrosis and Delayed Apoptosis

“…First, calcium influx may initially stimulate mitochondrial respiration (Hansford, 1985;McCormack et al, 1990;Li et al, 1996). As a suicide inhibitor, 3-NP inactivates SDH more rapidly when the enzyme activity is higher (Alston et al, 1977). Second, calcium and sodium influx may stimulate the consumption of ATP through Ca 2ϩ -ATPase and Na ϩ /K ϩ -ATPase.…”

“…In some studies, however, NMDA receptor antagonists attenuated but did not prevent neuronal death, suggesting that there is an NMDA-independent mechanism (Weller and Paul, 1993;Fink et al, 1996). Recently, Behrens and colleagues (1995) reported that 3-nitropropionic acid (3-NP), a suicide inhibitor of the mitochondrial enzyme succinate dehydrogenase (SDH) (Alston et al, 1977), induced apoptosis in neuronal cultures and that excitotoxicity was not involved.…”

Neuronal Pyruvate Carboxylation Supports Formation of Transmitter Glutamate

“…Labeling of aspartate, glutamate, and glutamine from [1-14 C]pyruvate therefore reflects pyruvate carboxylation. We used 3-nitropropionic acid to block the TCA cycle at the level of succinate dehydrogenase (Alston et al, 1977), leaving pyruvate carboxylation the only route for 14 C to enter the TCA cycle (Fig. 1) (Hassel et al, 1992(Hassel et al, , 1997Waniewski and Martin, 1998) to determine whether pyruvate carboxylation occurs in neurons in vivo.…”