Hydrogen abstraction by triplet flavins. I: time-resolved multi-channel absorption spectra of flash-irradiated riboflavin solutions in water

Melø, Thor Bernt; Ionescu, Maria Adriana; Haggquist, Gregory W.; Naqvi, K. Razi

doi:10.1016/s1386-1425(99)00097-9

Cited by 34 publications

(3 citation statements)

References 13 publications

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“…The primary photochemistry of RF in water is not field sensitive, as there is no appropriate electron donor to quench the photoexcited RF triplet state. However, it has been demonstrated that the reaction of two excited RF triplets can produce a pair of RF radical ions, 13 3 RF * + 3 RF * → RF + + RF − ,…”

Section: Resultsmentioning

confidence: 99%

Time-resolved optical absorption microspectroscopy of magnetic field sensitive flavin photochemistry

Antill

Beardmore

Woodward

2018

Review of Scientific Instruments

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The photochemical reactions of blue-light receptor proteins have received much attention due to their very important biological functions. In addition, there is also growing evidence that the one particular class of such proteins, the cryptochromes, may be associated with not only a biological photo-response but also a magneto-response, which may be responsible for the mechanism by which many animals can respond to the weak geomagnetic field. Therefore, there is an important scientific question over whether it is possible to directly observe such photochemical processes, and indeed the effects of weak magnetic fields thereon, taking place both in purified protein samples in vitro and in actual biochemical cells and tissues. For the former samples, the key lies in being able to make sensitive spectroscopic measurements on very small volumes of samples at potentially low protein concentrations, while the latter requires, in addition, spatially resolved measurements on length scales smaller than typical cellular components, i.e., sub-micron resolution. In this work, we discuss a two- and three-color confocal pump-probe microscopic approach to this question which satisfies these requirements and is thus useful for experimental measurements in both cases.

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Section: Resultsmentioning

confidence: 99%

Time-resolved optical absorption microspectroscopy of magnetic field sensitive flavin photochemistry

Antill

Beardmore

Woodward

2018

Review of Scientific Instruments

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“…Natural candidates are Trp and Tyr. The neutral tyrosyl radical, TyrO ● , is known to have solely a narrow absorption peak around 405 nm in the visible range 39 , 40 , while the corresponding Trp ● has a distinct absorption between 440 nm and 580 nm 41 , 42 , indicating that Trp ● is more likely the counter-radical of FMNH ● . TrpH ●+ absorbs as well in the visible range with a broad absorption band between 450 and 650 nm exhibiting a maximum at 560 nm and additionally at 335 nm 42 , but since the neutral FMNH ● is formed, the corresponding radical species of the electron donor is most likely also present in its neutral state.…”

Section: Resultsmentioning

confidence: 99%

Electron transfer pathways in a light, oxygen, voltage (LOV) protein devoid of the photoactive cysteine

Kopka

Magerl

Savitsky

et al. 2017

Sci Rep

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Blue-light absorption by the flavin chromophore in light, oxygen, voltage (LOV) photoreceptors triggers photochemical reactions that lead to the formation of a flavin-cysteine adduct. While it has long been assumed that adduct formation is essential for signaling, it was recently shown that LOV photoreceptor variants devoid of the photoactive cysteine can elicit a functional response and that flavin photoreduction to the neutral semiquinone radical is sufficient for signal transduction. Currently, the mechanistic basis of the underlying electron- (eT) and proton-transfer (pT) reactions is not well understood. We here reengineered pT into the naturally not photoreducible iLOV protein, a fluorescent reporter protein derived from the Arabidopsis thaliana phototropin-2 LOV2 domain. A single amino-acid substitution (Q489D) enabled efficient photoreduction, suggesting that an eT pathway is naturally present in the protein. By using a combination of site-directed mutagenesis, steady-state UV/Vis, transient absorption and electron paramagnetic resonance spectroscopy, we investigate the underlying eT and pT reactions. Our study provides strong evidence that several Tyr and Trp residues, highly conserved in all LOV proteins, constitute the eT pathway for flavin photoreduction, suggesting that the propensity for photoreduction is evolutionary imprinted in all LOV domains, while efficient pT is needed to stabilize the neutral semiquinone radical.

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“…A natural candidate would be an amino acid residue in LOV that acts as internal electron donor. However, tryptophan radicals have a band in the wavelength region longer than 500 nm, [41][42][43][44] histidine radicals absorb only shorter than 350 nm, and tyrosine radicals show a narrow band near 410 nm. 45,46 Hence tryptophan and histidine can be excluded as candidates, and tyrosine could only account for part of the absorption.…”

Section: Reaction With Thioether and Other Mutantsmentioning

confidence: 99%

Photoreaction of mutated LOV photoreceptor domains from Chlamydomonas reinhardtii with aliphatic mercaptans: implications for the mechanism of wild type LOV

Lanzl

Sanden-Flohe

Kutta

et al. 2010

Phys. Chem. Chem. Phys.

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Irradiation of the LOV1 domain from the blue-light photoreceptor phototropin of the green alga Chlamydomonas reinhardtii leads to the formation of a covalent adduct of the sulfur atom of cysteine 57 to the carbon C(4a) in the chromophore FMN. This reaction is not possible in the mutant LOV1-C57G in which this cysteine is replaced by glycine. Irradiation of LOV1-C57G in the absence of oxygen but in the presence of aliphatic mercaptans or thioethers leads to the formation of a species with an absorption maximum at 615 nm, which is identified as the neutral radical FMNH . When oxygen is admitted, the reaction is completely reversible. Irradiation of LOV1-C57G in the presence of methylmercaptan CH(3)SH under oxygen-free conditions yields, in addition to FMNH , a third species with a single absorption maximum at 379 nm. This species is stable against oxygen and is also formed when the irradiation is performed in the presence of oxygen. This species is assigned to the adduct between CH(3)SH and FMN. In aqueous solution the photoreaction of CH(3)SH with FMN leads to the fully reduced hydroquinone form FMNH(2) or its anion FMNH(-). Adduct formation apparently requires the protein cage. After formation, the adduct is stable for hours inside the protein, but decomposes immediately upon denaturation. The implications of these observations for the mechanism of adduct formation in wild type LOV domains are discussed.

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Hydrogen abstraction by triplet flavins. I: time-resolved multi-channel absorption spectra of flash-irradiated riboflavin solutions in water

Cited by 34 publications

References 13 publications

Time-resolved optical absorption microspectroscopy of magnetic field sensitive flavin photochemistry

Time-resolved optical absorption microspectroscopy of magnetic field sensitive flavin photochemistry

Electron transfer pathways in a light, oxygen, voltage (LOV) protein devoid of the photoactive cysteine

Photoreaction of mutated LOV photoreceptor domains from Chlamydomonas reinhardtii with aliphatic mercaptans: implications for the mechanism of wild type LOV

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