Electronic properties of flavins: Implications on the reactivity and absorption properties of flavoproteins

Wouters, Jan; Durant, François; Champagne, Benoı̂t; André, Jean‐Marie

doi:10.1002/(sici)1097-461x(1997)64:6<721::aid-qua9>3.0.co;2-y

Cited by 17 publications

(16 citation statements)

References 41 publications

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“…Recently, the structure of the reduced form of NTR was determined, at lower resolution than that of the Enterobacter cloaccae enzyme (15), and again very little structural difference between oxidized and reduced enzyme was observed. However, there is a large change in the electron distribution of the FMN ring system upon reduction, partly due to the addition of electrons and also due to the change in delocalization (33). This is reflected, for example, in the pK a values of N5 of the free flavin.…”

Section: Table IV Inhibition Patterns and Dissociation Constants For mentioning

confidence: 99%

Structural and Mechanistic Studies of Escherichia coli Nitroreductase with the Antibiotic Nitrofurazone

Race

Lovering

Green

et al. 2005

Journal of Biological Chemistry

191

243

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The antibiotics nitrofurazone and nitrofurantoin are used in the treatment of genitourinary infections and as topical antibacterial agents. Their action is dependent upon activation by bacterial nitroreductase flavoproteins, including the Escherichia coli nitroreductase (NTR). Here we show that the products of reduction of these antibiotics by NTR are the hydroxylamine derivatives. We show that the reduction of nitrosoaromatics is enzyme-catalyzed, with a specificity constant ϳ10,000-fold greater than that of the starting nitro compounds. This suggests that the reduction of nitro groups proceeds through two successive, enzyme-mediated reactions and explains why the nitroso intermediates are not observed. The global reaction rate for nitrofurazone determined in this study is over 10-fold higher than that previously reported, suggesting that the enzyme is much more active toward nitroaromatics than previously estimated. Surprisingly, in the crystal structure of the oxidized NTR-nitrofurazone complex, nitrofurazone is oriented with its amide group, rather than the nitro group to be reduced, positioned over the reactive N5 of the FMN cofactor. Free acetate, which acts as a competitive inhibitor with respect to NADH, binds in a similar orientation. We infer that the orientation of bound nitrofurazone depends upon the redox state of the enzyme. We propose that the charge distribution on the FMN rings, which alters upon reduction, is an important determinant of substrate binding and reactivity in flavoproteins with broad substrate specificity.

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Section: Table IV Inhibition Patterns and Dissociation Constants For mentioning

confidence: 99%

Structural and Mechanistic Studies of Escherichia coli Nitroreductase with the Antibiotic Nitrofurazone

Race

Lovering

Green

et al. 2005

Journal of Biological Chemistry

191

243

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“…Several mechanisms have been proposed and studied with different experimental and theoretical methods in reactions involving this cofactor 4, 34, 35. In addition, quantum mechanical calculations have been used to explore the electronic structure of the isolated isoalloxazine ring in the reduced and oxidized states 36–39. However, no calculations have been reported for flavins in a protein environment.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of NAD(P)H:Quinone reductase: Ab initio studies of reduced flavin

Cavelier

Amzel

2001

Proteins

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NAD(P)H:quinone oxidoreductase type 1 (QR1, NQO1, formerly DT-diaphorase; EC 1.6.99.2) is an FAD-containing enzyme that catalyzes the nicotinamide nucleotide-dependent reduction of quinones, quinoneimines, azo dyes, and nitro groups. Animal cells are protected by QR1 from the toxic and neoplastic effects of quinones and other electrophiles. Alternatively, in tumor cells QR can activate a number of cancer chemotherapeutic agents such as mitomycins and aziridylbenzoquinones. Thus, the same enzyme that protects the organism from the deleterious effects of quinones can activate cytotoxic chemotherapeutic prodrugs and cause cancer cell death. The catalytic mechanism of QR includes an important initial step in which FAD is reduced by NAD(P)H. The unfavorable charge separation that results must be stabilized by the protein. The details of this charge stabilization step are inaccessible to easy experimental verification but can be studied by quantum chemistry methods. Here we report ab initio quantum mechanical calculations in and around the active site of the enzyme that provide information about the fine details of the contribution of the protein to the stabilization of the reduced flavin. The results show that (1) protein interactions provide approximately 2 kcal/mol to stabilize the planar conformation of the reduced flavin isoalloxazine ring observed in the X-ray structure; (2) the charge separation present in the reduced planar form of the flavin is stabilized by interactions with groups of the protein; (3) even after stabilization, the reduction potential of the cofactor remains more negative than that of the free flavin, making it a better reductant for a larger variety of quinones; and (4) the more negative reduction potential may also result in faster kinetics for the quinone reduction step.

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“…Numerous quantum chemical calculations on flavins have already been reported in the literature. Most of them were on the semiempirical (18–22) some on the ab initio level of theory (23–26). In the present work some of these (ground state) calculations are repeated using the DFT B3LYP/6‐31G* model chemistry; in addition, TD‐DFT was applied to calculate the excited states of the flavin molecules and to estimate spectra using .…”

mentioning

confidence: 99%

“…Excited states of flavins have so far been computed using the semiempirical configuration interaction–Pariser‐Pople‐Parr (PPP) (19) and configuration interaction with singles–complete neglect of differential overlap (CIS‐CNDO) (26) methods, respectively. For an ab initio treatment of excited states of flavins see Neiß et al (16).…”

mentioning

confidence: 99%

Ab Initio Quantum Chemical Investigation of the First Steps of the Photocycle of Phototropin: A Model Study¶

Neiß¹,

Saalfrank²

2007

Photochemistry and Photobiology

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Phototropin is a blue light-activated photoreceptor that plays a dominant role in the phototropism of plants. The protein contains two subunits that bind flavin mononucleotide (FMN), which are responsible for the initial steps of the light-induced reaction. It has been proposed that the photoexcited flavin molecule adds a cysteine residue of the protein backbone, thus activating autophosphorylation of the enzyme. In this study, the electronic properties of several FMN-related compounds in different charge and spin states are characterized by means of ab initio quantum mechanical calculations. The model compounds serve as idealized model chromophores for phototropism. Reaction energies are estimated for simple model reactions, roughly representing the addition of a cysteine residue to the flavin molecule. Excitation energies were calculated with the help of time-dependent density functional theory. On the basis of these calculations we propose the following mechanism for the addition reaction: (1) after photoexcitation of FMN out of the singlet ground state S 0 , excited singlet state(s) are populated; these relax to the lowest excited singlet state S 1 , and subsequently by intersystem crossing FMN in the lowest triplet state, T 1 is formed; (2) the triplet easily removes the neutral hydrogen atom from the H-S group of the cysteine residue; and (3) the resulting thio radical is added.

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Electronic properties of flavins: Implications on the reactivity and absorption properties of flavoproteins

Cited by 17 publications

References 41 publications

Structural and Mechanistic Studies of Escherichia coli Nitroreductase with the Antibiotic Nitrofurazone

Structural and Mechanistic Studies of Escherichia coli Nitroreductase with the Antibiotic Nitrofurazone

Mechanism of NAD(P)H:Quinone reductase: Ab initio studies of reduced flavin

Ab Initio Quantum Chemical Investigation of the First Steps of the Photocycle of Phototropin: A Model Study¶

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