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1

Single-and two-electron reduction of quinones by flavoenzymes: mechanisms and implications for quinone cytotoxicity

100%
Cenas N., Nemeikaite-Ceniene A., Sarlauskas J., Acaite J.
Acta Biochimica Polonica
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2003
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tom 50
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nr Supplement 1
2

Reduction of nitroaromatic compounds by NAD(P)H:quinone oxidoreductase (NQO1): the role of electron-accepting potency and structural parameters in the substrate specificity

100%
Miseviciene L., Anusevicius Z., Sarlauskas J., Cenas N.
Acta Biochimica Polonica
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2006
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tom 53
|
nr 3
3

Role of NAD[P]H: quinone oxidoreductase [NQO1] in apoptosis induction by aziridinylbenzoquinones RH1 and MeDZQ

100%
Nemeikaite-Ceniene A., Dringeliene A., Sarlauskas J., Cenas N.
Acta Biochimica Polonica
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2005
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tom 52
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nr 4
We aimed to characterize the role of NAD(P)H : quinone oxidoreductase (NQO1) in apoptosis induction by antitumour quinones RH1 (2,5-diaziridinyl-3-hydroxymethyl-6-methyl-1,4-benzoquinone) and MeDZQ (2,5-dimethyl-3,6-diaziridinyl-1,4-benzoquinone). Digitonin-permeabilized FLK cells catalyzed NADPH-dependent single- and two-electron reduction of RH1 and MeDZQ. At equitoxic concentrations, RH1 and MeDZQ induced apoptosis more efficiently than the nonalkylating duroquinone or H2O2. The antioxidant N,N'-diphenyl-p-phenylene diamine, desferrioxamine, and the inhibitor of NQO1 dicumarol, protected against apoptosis induction by all compounds investigated, but to a different extent. The results of multiparameter regression analysis indicate that RH1 and MeDZQ most likely induce apoptosis via NQO1-linked formation of alkylating species but not via NQO1-linked redox cycling.
4

Redox properties and prooxidant cytotoxicity of a neuroleptic agent 6,7-dinitrodihydroquinoxaline-2,3-dione (DNQX)

76%
Sarlauskas J., Nemeikaite-Ceniene A., Miseviciene L., Krikstopaitis K., Anusevicius Z., Cenas N.
Acta Biochimica Polonica
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2013
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tom 60
|
nr 2
 In order to characterize the possible mechanism(s) of cytotoxicity of a neuroleptic agent 6,7-dinitrodihydroquinoxaline-2,3-dione (DNQX) we examined the redox properties of DNQX, and its mononitro- (NQX) and denitro- (QX) derivatives. The irreversible electrochemical reduction of the nitro groups of DNQX was characterized by the reduction peak potentials (Ep,7) of -0.43 V and -0.72 V vs. Ag/AgCl at pH 7.0, whereas NQX was reduced at Ep,7 = -0.67 V. The reactivities of DNQX and NQX towards the single-electron transferring enzymes NADPH:cytochrome P-450 reductase and NADPH:adrenodoxin reductase/adrenodoxin complex were similar to those of model nitrobenzenes with the single-electron reduction potential (E17) values of -0.29 V - -0.42 V. DNQX and NQX also acted as substrates for two-electron transferring mammalian NAD(P)H:quinone oxidoreductase (DT-diaphorase). The cytotoxicity of DNQX in bovine leukemia virus-transformed lamb kidney fibroblasts (line FLK) was prevented by antioxidants and an inhibitor of NQO1, dicoumarol, and was enhanced by the prooxidant alkylating agent 1,3-bis(2-chloromethyl)-1-nitrosourea. A comparison with model nitrobenzene compounds shows that the cytotoxicity of DNQX and NQX reasonably agrees with the ease of their electrochemical reduction, and/or their reactivities towards the used enzymatic single-electron reducing systems. Thus, our data imply that the cytotoxicity of DNQX in FLK cells is exerted mainly through oxidative stress.
5

Single-electron reduction of quinone and nitroaromatic xenobiotics by recombinant rat neuronal nitric oxide synthase

76%
Anusevicius Z., Nivinskas H., Sarlauskas J., Sari M.-A., Boucher J.-L., Cenas N.
Acta Biochimica Polonica
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2013
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tom 60
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nr 2
 We examined the kinetics of single-electron reduction of a large number of structurally diverse quinones and nitroaromatic compounds, including a number of antitumour and antiparasitic drugs, and nitroaromatic explosives by recombinant rat neuronal nitric oxide synthase (nNOS, EC 1.14.13.39), aiming to characterize the role of nNOS in the oxidative stress-type cytotoxicity of the above compounds. The steady-state second-order rate constants (kcat/Km) of reduction of the quinones and nitroaromatics varied from 102 M-1s-1 to 106 M-1s-1, and increased with an increase in their single-electron reduction potentials (E17). The presence of Ca2+/calmodulin enhanced the reactivity of nNOS. These reactions were consistent with an "outer sphere" electron-transfer mechanism, considering the FMNH·/FMNH2 couple of nNOS as the most reactive reduced enzyme form. An analysis of the reactions of nNOS within the 'outer sphere' electron-transfer mechanism gave the approximate values of the distance of electron transfer, 0.39-0.47 nm, which are consistent with the crystal structure of the reductase domain of nNOS. On the other hand, at low oxygen concentrations ([O2] = 40-50 µM), nNOS performs a net two-electron reduction of quinones and nitroaromatics. This implies that NOS may in part be responsible for the bioreductive alkylation by two-electron reduced forms of antitumour aziridinyl-substituted quinones under a modest hypoxia.
6

Two-electron reduction of quinones by Enterobacter cloacae PB2 pentaerythritol tetranitrate reductase: quantitative structure-activity relationships

76%
Miseviciene L., Anusevicius Z., Sarlauskas J., Harris R. J., Scrutton N. S., Cenas N.
Acta Biochimica Polonica
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2007
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tom 54
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nr 2
In order to clarify the poorly understood mechanisms of two-electron reduction of quinones by flavoenzymes, we examined the quinone reductase reactions of a member of a structurally distinct old yellow enzyme family, Enterobacter cloacae PB2 pentaerythritol tetranitrate reductase (PETNR). PETNR catalyzes two-electron reduction of quinones according to a 'ping-pong' scheme. A multiparameter analysis shows that the reactivity of quinones increases with an increase in their single-electron reduction potential and pKa of their semiquinones (a three-step (e-,H+,e-) hydride transfer scheme), or with an increase in their hydride-transfer potential (E7(H-)) (a single-step (H-) hydride transfer scheme), and decreases with a decrease in their van der Waals volume. However, the pH-dependence of PETNR reactivity is more consistent with a single-step hydride transfer. A comparison of X-ray data of PETNR, mammalian NAD(P)H: quinone oxidoreductase (NQO1), and Enterobacter cloacae nitroreductase, which reduce quinones in a two-electron way, and their reactivity revealed that PETNR is much less reactive, and much less sensitive to the quinone substrate steric effects than NQO1. This may be attributed to the lack of π-π stacking between quinone and the displaced aromatic amino acid in the active center, e.g., with Phe-178' in NQO1.
7

Enzymatic redox reactions of the explosive 4,6-dinitrobenzofuroxan [DNBF]: implications for its toxic action

76%
Nemeikaite-Ceniene A., Sarlauskas J., Miseviciene L., Anusevicius Z., Maroziene A., Cenas N.
Acta Biochimica Polonica
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2004
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tom 51
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nr 4
With an aim to understand the toxicity mechanisms of the explosive 4,6-dinitro- benzofuroxan (DNBF), we studied its single-electron reduction by NADPH:cyto- chrome P450 reductase and ferredoxin: NADP reductase, and two- electron reduc­tion by DT-diaphorase and Enterobacter cloacae nitroreductase. The enzymatic reac­tivities of DNBF and another explosive 2,4,6-trinitrotoluene (TNT) were similar, ex­cept for the much lower reactivity of DNBF towards nitroreductase. DNBF was less cytotoxic in FLK cells than TNT. However, their action shared the same mechanisms, oxidative stress and activation by DT-diaphorase. The lower cytotoxicity of DNBF may be explained by the negative electrostatic charge of its adduct with water which may impede cellular membrane penetration, and by the formation of its less reactive adducts with intracellular reduced glutathione.
8

Two-electron reduction of nitroaromatic compounds by Enterobacter cloacae NAD[P]H nitroreductase: description of quantitative structure - activity relationships

76%
Nivinskas H., Koder R. L., Anusevicius Z., Sarlauskas J., Miller A. F., Cenas N.
Acta Biochimica Polonica
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2000
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tom 47
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nr 4
Enterobacter cloacae NAD(P)H:nitroreductase catalyzes the reduction of a series of nitroaromatic compounds with steady-state bimolecular rate constants (kcat/Km) ranging from 104 M-1s-1 to 107 M-1s-1, and oxidizing 2 moles NADH per mole mononitrocompound. Oxidation of excess NADH by polynitrobenzenes including explosives 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenyl-N-methylnitramine (tetryl), has been observed as a slower secondary process, accompanied by O2 consumption. This type of 'redox cycling' was not related to reactions of nitroaromatic anion-radicals, but was caused by the autoxidation of relatively stable reaction products. The logs kcat/Km of all the compounds examined exhibited parabolic dependence on their enthalpies of single-electron- or two-electron (hydride) reduction, obtained by quantum mechanical calculations. This type of quantitative structure-activity relationships shows that the reactivity of nitroaromatics towards E. cloacae nitroreductase depends mainly on their hydride accepting properties, but not on their particular structure, and does not exclude the possibility of multistep hydride transfer.
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