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Molecules 2018, 23(7), 1672; https://doi.org/10.3390/molecules23071672

Mechanism of Two-/Four-Electron Reduction of Nitroaromatics by Oxygen-Insensitive Nitroreductases: The Role of a Non-Enzymatic Reduction Step

1
Department of Xenobiotics Biochemistry, Institute of Biochemistry of Vilnius University, Saulėtekio 7, LT-10257 Vilnius, Lithuania
2
School of Biological Sciences, Victoria University of Wellington, Kelburn Parade, Wellington 6140, New Zealand
*
Author to whom correspondence should be addressed.
Received: 13 June 2018 / Revised: 2 July 2018 / Accepted: 5 July 2018 / Published: 9 July 2018
(This article belongs to the Section Organic Chemistry)
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Abstract

Oxygen-insensitive NAD(P)H:nitroreductases (NR) reduce nitroaromatics (Ar-NO2) into hydroxylamines (Ar-NHOH) through nitroso (Ar-NO) intermediates. Ar-NO may be reduced both enzymatically and directly by reduced nicotinamide adenine dinucleotide or its phosphate NAD(P)H, however, it is unclear which process is predominant in catalysis of NRs. We found that E. coli NR-A (NfsA) oxidizes 2 mol of NADPH per mol of 2,4,6-trinitrotoluene (TNT) and 4 mol of NADPH per mol of tetryl. Addition of ascorbate, which reduces Ar-NO into Ar-NHOH, changes the stoichiometry NADPH/Ar-NO2 into 1:1 (TNT) and 2:1 (tetryl), and decreases the rate of NADPH oxidation. Ascorbate does not interfere with the oxidation of NADPH during reduction of quinones by NfsA. Our analysis of ascorbate inhibition patterns and both enzymatic and non-enzymatic reduction of nitrosobenzene suggests that direct reduction of Ar-NO by NADPH rather than enzymatic reduction is the predominant mechanism during nitroaromatic reduction. View Full-Text
Keywords: nitroreductase; aromatic nitrocompounds; reduction mechanism nitroreductase; aromatic nitrocompounds; reduction mechanism
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Valiauga, B.; Misevičienė, L.; Rich, M.H.; Ackerley, D.F.; Šarlauskas, J.; Čėnas, N. Mechanism of Two-/Four-Electron Reduction of Nitroaromatics by Oxygen-Insensitive Nitroreductases: The Role of a Non-Enzymatic Reduction Step. Molecules 2018, 23, 1672.

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