Structure and properties of 5-deazaflavin radicals as compared to natural flavosemiquinones

Goldberg, M; Pecht, Israel; Kramer, Horst E. A.; Traber, Rainer; Hemmerich, Peter

doi:10.1016/0304-4165(81)90487-6

Cited by 41 publications

(14 citation statements)

References 30 publications

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“…Also, apart from the increase in absorbance below 310 nm due to the formation of DS2 in reaction [7], the initial flavin absorption was completely restored on the addition of air. These observations are consistent with dihydroflavin as the only major product, formed via reactions [7], [6], and [8a-c] or [9].…”

Section: Pulse Radiolysissupporting

confidence: 87%

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The one- and two-electron reduction of 2-thioriboflavin by radical anions of CO₂ and dithiothreitol

Surdhar¹,

Massey²

1986

Can. J. Chem.

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. Can. J. Chem. 64,67 (1986). The one-and two-electron reductions of 2-thioriboflavin with .COT and cyclic disulphide anion of dithiothreitol (DS?.) have been studied by the steady state y and pulse radiolysis techniques. The .COT radical reacted with 2-thioriboflavin to give the neutral semiquinone (.FIH) and the radical anion (.F1-) at pH 5 and 10 respectively. The pK of the .FIH radical was determined to be 7.4. In the case of the anion, the 2-thioriboflavin spectrum is similar in shape to that of FAD radical anion, but red shifted by 40-50 nm. Red shifts are also seen in the neutral .FIH form for the 370-nm peak and 580-nm shoulder. However, in addition, there is strong enhancement of the absorbance at 500 nm. The spectrum of 2-thioriboflavin semiquinone produced in the presence of 2-5 mM dithiothreitol was perturbed, as was observed previously for unsubstituted flavin semiquinones in the presence of sulphydryls. The rate constants for the initial one-electron reduction step viz: [5] F1 + .COT -, .F1-+ C 0 2 were 4.0 ? 0.5 X lo9 M-' s-' and 1.3 & 0.2 X 109 M-' s-' at pH 7 and 10 respectively. The corresponding rate for the reaction of DS;. with 2-thioriboflavin at pH 7 was determined to be 2.4 * 0.2 X lo9 M-Is-'. The continuous production of DS;. radicals by y radiolysis reduced 2-thioriboflavin to the dihydro form, and the flavin was regenerated on the addition of air. The .COT radical also effected a two-electron reduction. However, in this case, if the process was taken beyond the equivalence point, the dihydroflavin spectrum was bleached and the oxidized flavin could not be recovered.

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Section: Pulse Radiolysissupporting

confidence: 87%

“…The experiments were performed by the pulse radiolysis technique (5), which was also utilized in earlier examinations of flavin semiquinones (6)(7)(8)(9). The reducing radicals .COT and DST.…”

Section: Introductionmentioning

confidence: 99%

The one- and two-electron reduction of 2-thioriboflavin by radical anions of CO₂ and dithiothreitol

Surdhar¹,

Massey²

1986

Can. J. Chem.

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“…One is the lower redox midpoint potential of F 420 in solvent at pH 7.5 (−350 mV for F 420 versus −230 mV for FMN) (Draper and Ingraham, 1968; Jacobson and Walsh, 1984). The other is that F 420 is not stable as a semiquinone and may only catalyse a two electron reduction, while FMN may catalyse one or two electron reduction and oxidation reactions (Goldberg et al ., 1981). Indeed, owing to this, the chemistry that is generally catalysed by the two enzyme families is opposite (oxidation by the PNPOxs versus reduction by the FDRs).…”

Section: Discussionmentioning

confidence: 99%

Identification and characterization of two families of F₄₂₀H₂‐dependent reductases from Mycobacteria that catalyse aflatoxin degradation

Taylor

Jackson

Tattersall

et al. 2010

Molecular Microbiology

144

197

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Aflatoxins are polyaromatic mycotoxins that contaminate a range of food crops as a result of fungal growth and contribute to serious health problems in the developing world because of their toxicity and mutagenicity. Although relatively resistant to biotic degradation, aflatoxins can be metabolized by certain species of Actinomycetales. However, the enzymatic basis for their breakdown has not been reported until now. We have identified nine Mycobacterium smegmatis enzymes that utilize the deazaflavin cofactor F420H2 to catalyse the reduction of the α,β-unsaturated ester moiety of aflatoxins, activating the molecules for spontaneous hydrolysis and detoxification. These enzymes belong to two previously uncharacterized F420H2 dependent reductase (FDR-A and -B) families that are distantly related to the flavin mononucleotide (FMN) dependent pyridoxamine 5′-phosphate oxidases (PNPOxs). We have solved crystal structures of an enzyme from each FDR family and show that they, like the PNPOxs, adopt a split barrel protein fold, although the FDRs also possess an extended and highly charged F420H2 binding groove. A general role for these enzymes in xenobiotic metabolism is discussed, including the observation that the nitro-reductase Rv3547 from Mycobacterium tuberculosis that is responsible for the activation of bicyclic nitroimidazole prodrugs belongs to the FDR-A family.

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“…Despite this fact, there is no precedence of reductive processes involving this radical species. This might result from the very low stability of the dFl sq free in the solution 3,5,48 .…”

mentioning

confidence: 99%

Deazaflavin reductive photocatalysis involves excited semiquinone radicals

et al. 2020

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Flavin-mediated photocatalytic oxidations are established in synthetic chemistry. In contrast, their use in reductive chemistry is rare. Deazaflavins with a much lower reduction potential are even better suited for reductive chemistry rendering also deazaflavin semiquinones as strong reductants. However, no direct evidence exists for the involvement of these radical species in reductive processes. Here, we synthesise deazaflavins with different substituents at C5 and demonstrate their photocatalytic activity in the dehalogenation of p-halogenanisoles with best performance under basic conditions. Mechanistic investigations reveal a consecutive photo-induced electron transfer via the semiquinone form of the deazaflavin as part of a triplet-correlated radical pair after electron transfer from a sacrificial electron donor to the triplet state. A second electron transfer from the excited semiquinone to p-halogenanisoles triggers the final product formation. This study provides first evidence that the reductive power of excited deazaflavin semiquinones can be used in photocatalytic reductive chemistry.

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Structure and properties of 5-deazaflavin radicals as compared to natural flavosemiquinones

Cited by 41 publications

References 30 publications

The one- and two-electron reduction of 2-thioriboflavin by radical anions of CO₂ and dithiothreitol

The one- and two-electron reduction of 2-thioriboflavin by radical anions of CO₂ and dithiothreitol

Identification and characterization of two families of F₄₂₀H₂‐dependent reductases from Mycobacteria that catalyse aflatoxin degradation

Deazaflavin reductive photocatalysis involves excited semiquinone radicals

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Structure and properties of 5-deazaflavin radicals as compared to natural flavosemiquinones

Cited by 41 publications

References 30 publications

The one- and two-electron reduction of 2-thioriboflavin by radical anions of CO2 and dithiothreitol

The one- and two-electron reduction of 2-thioriboflavin by radical anions of CO2 and dithiothreitol

Identification and characterization of two families of F420H2‐dependent reductases from Mycobacteria that catalyse aflatoxin degradation

Deazaflavin reductive photocatalysis involves excited semiquinone radicals

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The one- and two-electron reduction of 2-thioriboflavin by radical anions of CO₂ and dithiothreitol

The one- and two-electron reduction of 2-thioriboflavin by radical anions of CO₂ and dithiothreitol

Identification and characterization of two families of F₄₂₀H₂‐dependent reductases from Mycobacteria that catalyse aflatoxin degradation