title: 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) oxidoreductase, EC 1.3.99.1] as follows. (i) When rat liver mitochondria oxidize succinate in the presence of 3-nitropropionate carbanion, the rate of O(2) consumption decreases exponentially to a zero value. This pattern is duplicated by subsequent additions of mitochondria. The dependence of the apparent first-order rate constant for enzyme inhibition, as well as the number of enzyme turnovers completed before inhibition, on the concentrations of 3-nitropropionate carbanion and succinate are those expected for an active site-directed and irreversible inhibitor. (ii) The inactivated enzyme is not resuscitated by centrifugation and washing of the mitochondria, in contrast to malonate-treated enzyme, and malonate protects against irreversible, inhibition. (iii) The inhibitor species is 3-nitropropionate carbanion and no external nucleophile is required for inhibition. (iv) The respiratory rates, respiratory control ratios, and ADP/O ratios obtained with NAD-linked substrates are unaffected by 3-nitropropionate carbanion. These results show that 3-nitropropionate carbanion is a highly specific, time-dependent, and irreversible inhibitor of succinate dehydrogenase. By analogy with the reaction of nitroethane with D-amino acid oxidase, the data are consistent with the hypothesis that the carbanionic inhibitor forms a covalent N-5 adduct with the active site flavin. 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.
mesh_terms: D000818:Animals; D007700:Kinetics; D008297:Male; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism; D009574:Nitro Compounds / Q000494:pharmacology*; D010101:Oxygen Consumption / Q000187:drug effects; D010944:Plants; D011422:Propionates / Q000494:pharmacology*; D051381:Rats; D013385:Succinate Dehydrogenase / Q000037:antagonists & inhibitors*
chemical_list: D009574:Nitro Compounds; D011422:Propionates; D013385:Succinate Dehydrogenase; C015392:3-nitropropionic acid
references.citation: Biochim Biophys Acta. 1970 Mar 18;198(3):423-37
references.pmid: 5436154
references.citation: Adv Enzymol Relat Subj Biochem. 1956;17:65-134
references.pmid: 13313307
references.citation: Biochem J. 1958 Apr;68(4):647-53
references.pmid: 13522675
references.citation: Ther Ggw. 1964 Mar;103:168-71
references.pmid: 14129989
references.citation: J Biol Chem. 1951 Feb;188(2):685-93
references.pmid: 14824156
references.citation: Science. 1954 Mar 5;119(3088):322-3
references.pmid: 17754331
references.citation: J Biol Chem. 1977 Jun 25;252(12):4361-70
references.pmid: 16930
references.citation: J Biol Chem. 1973 Jun 25;248(12):4400-16
references.pmid: 4145800
references.citation: Biochim Biophys Acta. 1967 Mar 8;131(2):407-11
references.pmid: 4167439
references.citation: J Gen Physiol. 1965 Sep;49(1):Suppl:163-95
references.pmid: 4285727
references.citation: J Biol Chem. 1971 Nov 25;246(22):6855-66
references.pmid: 4399475
references.citation: J Biol Chem. 1972 Mar 25;247(6):1951-3
references.pmid: 4401156
references.citation: Z Naturforsch B. 1972 Sep;27(9):1052-3
references.pmid: 4405074
references.citation: Cancer Res. 1971 Nov;31(11):1564-9
references.pmid: 4941349
references.citation: Biochemistry. 1972 Feb 1;11(3):309-14
references.pmid: 5059115