Publications

• The biochemistry of the metabolic poison propionate 3-nitronate and its conjugate acid, 3-nitropropionate.

  Francis K., Smitherman C., Nishino S.F., Spain J.C., Gadda G.

  3-Nitropropionate (3-NPA) is a nitro aliphatic compound found in numerous plants and fungi. The nitro compound exists in equilibrium with its conjugate base, propionate 3-nitronate (P3N) and has a pKa approaching the physiological range of 9.1. Since 1920, more than 30 species of plant and fungi h ... >> More

  3-Nitropropionate (3-NPA) is a nitro aliphatic compound found in numerous plants and fungi. The nitro compound exists in equilibrium with its conjugate base, propionate 3-nitronate (P3N) and has a pKa approaching the physiological range of 9.1. Since 1920, more than 30 species of plant and fungi have been identified as producing 3-NPA as a means of defense from herbivores. Glycoside products containing moieties of 3-NPA found in parts of the plants most accessible to herbivores can be easily hydrolyzed to free 3-NPA by bacterial enzymes in the gut of animals. In addition to providing a defense mechanism, the nitro compound is an intermediate in the nitrification process of leguminous plants. The synthesis of 3-NPA in these plants and fungi is poorly understood. P3N, which readily forms from 3-NPA at physiological pH, is a potent inhibitor of the key enzyme succinate dehydrogenase in the Krebs cycle and electron transport chain. Inhibition of succinate dehydrogenase in humans and livestock causes neurotoxicity and in some cases death. Several enzymes catalyze the oxidation of 3-NPA or P3N; all contain a noncovalently bound flavin cofactor and are found in the organisms that produce 3-NPA. With k(cat)/K(m) values of >10(6) M(-1) s(-1), nitronate monooxygenases can quickly and efficiently oxidize P3N to malonic semialdehyde as a means of protecting the organism from killing itself. Although it was discovered almost a century ago, the biochemistry and physiological role of 3-NPA/P3N are just emerging. << Less

  IUBMB Life 65:759-768(2013) [PubMed] [EuropePMC]

• Growth of bacteria on 3-nitropropionic acid as a sole source of carbon, nitrogen, and energy.

  Nishino S.F., Shin K.A., Payne R.B., Spain J.C.

  3-Nitropropionic acid (3NPA) is a widespread nitroaliphatic toxin found in a variety of legumes and fungi. Several enzymes have been reported that can transform the compound, but none led to the mineralization of 3NPA. We report here the isolation of bacteria that grow on 3NPA and its anion, propi ... >> More

  3-Nitropropionic acid (3NPA) is a widespread nitroaliphatic toxin found in a variety of legumes and fungi. Several enzymes have been reported that can transform the compound, but none led to the mineralization of 3NPA. We report here the isolation of bacteria that grow on 3NPA and its anion, propionate-3-nitronate (P3N), as the sole source of carbon, nitrogen, and energy. Experiments with resting cells, cell extracts, and purified enzymes indicate that the pathway involves conversion of 3NPA to P3N, which upon denitration yields malonic semialdehyde, nitrate, nitrite, and traces of H(2)O(2). Malonic semialdehyde is decarboxylated to acetyl coenzyme A. The gene that encodes the enzyme responsible for the denitration of P3N was cloned and expressed, and the enzyme was purified. Stoichiometry of the reaction indicates that the enzyme is a monooxygenase. The gene sequence is related to a large group of genes annotated as 2-nitropropane dioxygenases, but the P3N monooxygenase and closely related enzymes form a cluster within COG2070 that differs from previously characterized 2-nitropropane dioxygenases by their substrate specificities and reaction products. The results suggest that the P3N monooxygenases enable bacteria to exploit 3NPA in natural habitats as a growth substrate. << Less

  Appl. Environ. Microbiol. 76:3590-3598(2010) [PubMed] [EuropePMC]