Properties of flavins where the 8-methyl group is replaced by mercapto- residues.

Moore, Edwin G.; Ghisla, Sandro; Massey, Vincent

doi:10.1016/s0021-9258(19)86872-2

Cited by 76 publications

(45 citation statements)

References 21 publications

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“…With an edge-to-edge donor/acceptor distance similar to the C β separation of ~16.8 Å and a driving force of roughly −1.2 eV, electron tunneling between the cofactors should be on the microsecond timescale (Fig. 6), 25 too slow to be observed in these measurements.…”

Section: Discussionmentioning

confidence: 94%

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Ultrafast flavin/tryptophan radical pair kinetics in a magnetically sensitive artificial protein

Bialas

Barnard

Auman

et al. 2019

Phys. Chem. Chem. Phys.

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Section: Discussionmentioning

confidence: 94%

“…3D). Direct ligation of the cysteine to the flavin ring at the 8position systematically alters the spectroscopic properties compared to free riboflavin 25 as the Cys sulfur orbitals mix with the relevant flavin orbitals (Fig. 1).…”

Section: Resultsmentioning

confidence: 99%

Ultrafast flavin/tryptophan radical pair kinetics in a magnetically sensitive artificial protein

Bialas

Barnard

Auman

et al. 2019

Phys. Chem. Chem. Phys.

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“…When the electron donating effect of the sulfur is moderated by two covalently bound electronegative oxygens in a function like R x -SO 2 , the fluorescence quantum yield is between 45 to 70% the one of riboflavin. 63 Such results suggest that the extent of electron donation at C(8) position and subsequent extent of ICT character of the FMN has a direct influence on its fluorescence quantum yield and consequently on its singlet excited state lifetime. Very likely, enhanced ISC through interaction with the sulfur leads to the fluorescence quenching, as is the case in LOV2.…”

Section: Fmn Quinoid Character and Enhanced Isc To The Triplet Statementioning

confidence: 93%

“…The C(8) methyl group of flavins has an unexpectedly high reactivity. 63 Such intrinsic high reactivity has been used to characterise modified flavin derivatives containing different sulfur functions at the C(8) position and their fluorescence yield. Interestingly, when the C(8) position function is S À , the derivative has a strong ICT/quinoid character and no detectable fluorescence.…”

Section: Fmn Quinoid Character and Enhanced Isc To The Triplet Statementioning

confidence: 99%

Perturbation of the ground-state electronic structure of FMN by the conserved cysteine in phototropin LOV2 domains

Alexandre¹,

Grondelle²,

Hellingwerf³

et al. 2008

Phys. Chem. Chem. Phys.

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In LOV2, the blue-light sensitive domain of phototropin, the primary photophysical event involves intersystem crossing (ISC) from the singlet-excited state to the triplet state. The ISC rate is enhanced in LOV2 as compared to flavin mononucleotide (FMN) in solution, which likely results from a heavy-atom effect of a nearby conserved cysteine, C450. Here, we applied fluorescence line narrowing (FLN), resonance Raman (RR) and Fourier-transform infrared (FTIR) spectroscopy to investigate the electronic structure of FMN bound to Avena sativa LOV2 (AsLOV2), its C450A mutant and Adiantum LOV2 (Phy3LOV2). We demonstrate that FLN is the method of choice to obtain accurate vibrational spectra on highly fluorescent flavoproteins. The vibrational spectrum of AsLOV2-C450A showed small but significant shifts with respect to those of wild type AsLOV2 and Phy3LOV2, with a systematic down-shift of Ring I vibrations, upshifts of Ring II and III vibrations and an upshift of the C2=O mode. These trends are similar to those in FMN model systems with an electron-donating group substituted at Ring I, known to induce a quinoid character to the electronic structure of oxidized flavin. Thus, enhancement of the ISC rate in LOV2 is induced through weak electron donation by the cysteine which mixes the FMN pi-electrons with the heavy sulfur orbitals, manifesting itself in a quinoid character of the ground electronic state of oxidized FMN. The proximity of the cysteine to FMN thus not only enables formation of a covalent adduct between FMN and cysteine, but also facilitates the rapid electronic formation of the reactive FMN triplet state.

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“…27 Hence, the formation of the C4a-OO(H) species or other steps in the reaction may be influenced by inductive effects at the C8 position of FMN and could provide insights into the mechanism. 45 We these reduced flavin analogues observed at wavelengths corresponding to the C4a-OO(H) maxima determined in panels B, E, and H of Figure 4 revealed that substituents at C8 influenced the rates of formation of the C4a-OO(H) intermediates (Figure 4J). To quantify the effect of these substituents on the rate of formation of the C4a-OO(H) intermediates, reactions were initiated by mixing buffers containing a range of O 2 concentrations with an anaerobic solution of BluB bound to each reduced substituted flavin.…”

Section: ■ Results and Discussionmentioning

confidence: 86%

Unique Biochemical and Sequence Features Enable BluB To Destroy Flavin and Distinguish BluB from the Flavin Monooxygenase Superfamily

2018

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Vitamin B (cobalamin) is an essential micronutrient for humans that is synthesized by only a subset of bacteria and archaea. The aerobic biosynthesis of 5,6-dimethylbenzimidazole, the lower axial ligand of cobalamin, is catalyzed by the "flavin destructase" enzyme BluB, which fragments reduced flavin mononucleotide following its reaction with oxygen to yield this ligand. BluB is similar in sequence and structure to members of the flavin oxidoreductase superfamily, yet the flavin destruction process has remained elusive. Using stopped-flow spectrophotometry, we find that the flavin destructase reaction of BluB from Sinorhizobium meliloti is initiated with canonical flavin-O chemistry. A C4a-peroxyflavin intermediate is rapidly formed in BluB upon reaction with O, and has properties similar to those of flavin-dependent hydroxylases. Analysis of reaction mixtures containing flavin analogues indicates that both formation of the C4a-peroxyflavin and the subsequent destruction of the flavin to form 5,6-dimethylbenzimidazole are influenced by the electronic properties of the flavin isoalloxazine ring. The flavin destruction phase of the reaction, which results from the decay of the C4a-peroxyflavin intermediate, occurs more efficiently at pH >7.5. Furthermore, the BluB mutants D32N and S167G are specifically impaired in the flavin destruction phase of the reaction; nevertheless, both form the C4a-peroxyflavin nearly quantitatively. Coupled with a phylogenetic analysis of BluB and related flavin-dependent enzymes, these results demonstrate that the BluB flavin destructase family can be identified by the presence of active site residues D32 and S167.

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Properties of flavins where the 8-methyl group is replaced by mercapto- residues.

Cited by 76 publications

References 21 publications

Ultrafast flavin/tryptophan radical pair kinetics in a magnetically sensitive artificial protein

Ultrafast flavin/tryptophan radical pair kinetics in a magnetically sensitive artificial protein

Perturbation of the ground-state electronic structure of FMN by the conserved cysteine in phototropin LOV2 domains

Unique Biochemical and Sequence Features Enable BluB To Destroy Flavin and Distinguish BluB from the Flavin Monooxygenase Superfamily

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