3-Nitropropionic acid oxidase from horseshoe vetch (Hippocrepis comosa): a novel plant enzyme

Hipkin, C. R.; Salem, Mansour A.S.; Simpson, Deborah J.; Wainwright, S. J.

doi:10.1042/bj3400491

Cited by 20 publications

(12 citation statements)

References 17 publications

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“…Lack of detection of hydrogen peroxide among the products of the reaction would support the notion that the enzyme is a monooxygenase rather than an oxidase, as is also the case for the other fungal nitronate monooxygenases that have been investigated (43)(44)(45). The oxygen-dependent oxidation of 3-NPA to malonate semialdehyde is also catalyzed by an enzyme purified from H. comosa, a European herb of the family leguminosae (21). The enzyme was named 3-NPA oxidase, based on a specific activity with 3-NPA that was 30-fold more than that determined with other substrates and because H 2 O 2 was detected as a reaction product (21).…”

Section: Enzymes Oxidizing 3-npa/p3nmentioning

confidence: 81%

The biochemistry of the metabolic poison propionate 3‐nitronate and its conjugate acid, 3‐nitropropionate

et al. 2013

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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 pK a 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, 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. V C 2013 IUBMB Life, 65(9): [759][760][761][762][763][764][765][766][767][768] 2013

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Section: Enzymes Oxidizing 3-npa/p3nmentioning

confidence: 81%

The biochemistry of the metabolic poison propionate 3‐nitronate and its conjugate acid, 3‐nitropropionate

et al. 2013

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“…Moreover, nitrated proteins, amino acids, and metabolites often possess antibiotic activity and can mitigate bacterial and/or fungal infection (2,3). Some organisms, such as Penicillium atrovenetum (4) and Hippocrepis comosa, exploit these characteristics and produce nitroalkane compounds as a putative chemical defense mechanism (5,6). Typically, the organisms that produce nitroalkane toxins also produce enzymes that transform the nitroaliphatic internally and thus protect the host from the toxic effects of the agent (4,5).…”

mentioning

confidence: 99%

Crystal Structures of Nitroalkane Oxidase: Insights into the Reaction Mechanism from a Covalent Complex of the Flavoenzyme Trapped during Turnover

et al. 2006

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Nitroalkane oxidase (NAO) from Fusarium oxysporum catalyzes the oxidation of neutral nitroalkanes to the corresponding aldehydes or ketones with the production of H(2)O(2) and nitrite. The flavoenzyme is a new member of the acyl-CoA dehydrogenase (ACAD) family, but it does not react with acyl-CoA substrates. We present the 2.2 A resolution crystal structure of NAO trapped during the turnover of nitroethane as a covalent N5-FAD adduct (ES*). The homotetrameric structure of ES* was solved by MAD phasing with 52 Se-Met sites in an orthorhombic space group. The electron density for the N5-(2-nitrobutyl)-1,5-dihydro-FAD covalent intermediate is clearly resolved. The structure of ES was used to solve the crystal structure of oxidized NAO at 2.07 A resolution. The c axis for the trigonal space group of oxidized NAO is 485 A, and there are six subunits (1(1)/(2) holoenzymes) in the asymmetric unit. Four of the active sites contain spermine (EI), a weak competitive inhibitor, and two do not contain spermine (E(ox)). The active-site structures of E(ox), EI, and ES* reveal a hydrophobic channel that extends from the exterior of the protein and terminates at Asp402 and the N5 position on the re face of the FAD. Thus, Asp402 is in the correct position to serve as the active-site base, where it is proposed to abstract the alpha proton from neutral nitroalkane substrates. The structures for NAO and various members of the ACAD family overlay with root-mean-square deviations between 1.7 and 3.1 A. The homologous region typically spans more than 325 residues and includes Glu376, which is the active-site base in the prototypical member of the ACAD family. However, NAO and the ACADs exhibit differences in hydrogen-bonding patterns between the respective active-site base, substrate molecules, and FAD. These likely differentiate NAO from the homologues and, consequently, are proposed to result in the unique reaction mechanism of NAO.

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“…Nevertheless, certain bacteria, yeasts, fungi and at least one plant,47, 48 are known to use molecular oxygen in conversion of nitroalkanes to aldehydes or ketones, with reactions initiated by deprotonation of the nitroalkane by an active site base, so that some more direct comparisons are possible, and we conclude by drawing attention to those.…”

Section: Isotope Effects and Temperature Dependencesmentioning

confidence: 99%

Primary kinetic hydrogen isotope effects in deprotonations of carbon acids

Watt

2010

J of Physical Organic Chem

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The mechanisms of deprotonation of carbon acids are reviewed to emphasise the important kinetic consequences associated with the internal and solvent reorganisation in forming the conjugate base. Some practicalities of measurements of kinetic hydrogen isotope effects are then considered to show how competing reactions, exchange and mechanistic branching might affect these measurements. Finally, isotopic rate ratios (kH/kD) have been collected for non‐enzymic deprotonations of carbon acids for which temperature dependences have also been determined. All examples contain nitro groups. For reactions in hydroxylic solvents, only two examples are found for which kH/kD > 8 at 25 °C (28.8 and 10.7), possibly indicating a tunnelling contribution. In both cases, values of E aD–E aH are larger and values of AH/AD smaller than the range expected (E aD–E aH = 4.54 kJ mol−1 and 0.7 < AH/AD < 1.4) for effects arising from zero‐point energy differences with no tunnelling contributions. For reactions in aprotic solvents, isotope effects are larger (12.1 < kH/kD < 19.6), but again, the largest of these (19.6 and 15.8) are associated with elevated values of E aD–E aH and small values of AH/AD. It is pointed out that behaviour of this type is accommodated by corrections to the semi‐classical model with shallow tunnelling maximised by high symmetrical barriers. No examples have been found in which large effects are associated with large values of AH/AD and small values of E aD–E aH. Comparisons are made with two recently reported enzyme‐catalysed reactions involving deprotonation of nitroalkanes. Copyright © 2010 John Wiley & Sons, Ltd.

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3-Nitropropionic acid oxidase from horseshoe vetch (Hippocrepis comosa): a novel plant enzyme

Cited by 20 publications

References 17 publications

The biochemistry of the metabolic poison propionate 3‐nitronate and its conjugate acid, 3‐nitropropionate

The biochemistry of the metabolic poison propionate 3‐nitronate and its conjugate acid, 3‐nitropropionate

Crystal Structures of Nitroalkane Oxidase: Insights into the Reaction Mechanism from a Covalent Complex of the Flavoenzyme Trapped during Turnover

Primary kinetic hydrogen isotope effects in deprotonations of carbon acids

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