[153] Flavins as photosensitizers

Taylor, Meghan; Radda, George K.

doi:10.1016/s0076-6879(71)18110-4

Cited by 19 publications

(7 citation statements)

References 15 publications

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“…In this case, the greater extent of complexing and, perhaps more complete shielding of the flavin may contribute. In addition to tryptophan and tyrosine, the photooxidation of histidine, methionine, and cysteine in the presence of flavins has been shown to occur rather readily (Taylor and Radda, 1971). Although one pathway may again follow abstraction of hydrogen from such substrates by the flavin triplet, as is the main mechanism in the photooxidation of aliphatic amines and amino acids (Penzer, 1970), reaction of triplet with O2 to generate singlet oxygen, which then reacts, is certainly important for some of the aromatic amino acids.…”

Section: (A) Intermolecular Casesmentioning

confidence: 99%

“…Although one pathway may again follow abstraction of hydrogen from such substrates by the flavin triplet, as is the main mechanism in the photooxidation of aliphatic amines and amino acids (Penzer, 1970), reaction of triplet with O2 to generate singlet oxygen, which then reacts, is certainly important for some of the aromatic amino acids. It has been shown that the rates of reaction of the latter, including tyrosine and tryptophan, increase with oxygen concentration (Taylor and Radda, 1971 ). In the flavin-sensitized photooxidation of histidine, it has been demonstrated that a 1,4cycloaddi-tion of singlet oxygen to the imidazole ring produces a cyclic peroxide that decomposes to give aspartic acid via at least 17 intermediates (Tomita et al, 1969).…”

Section: (A) Intermolecular Casesmentioning

confidence: 99%

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Interactions of Flavins With Amino Acid Residues: Assessments From Spectral and Photochemical Studies

McCormick

1977

Photochem & Photobiology

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Section: (A) Intermolecular Casesmentioning

confidence: 99%

Section: (A) Intermolecular Casesmentioning

confidence: 99%

Interactions of Flavins With Amino Acid Residues: Assessments From Spectral and Photochemical Studies

McCormick

1977

Photochem & Photobiology

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“…However, it has been known for a long time that flavins can sensitise the destructive photooxidation of a large variety of substrates, such as amino acids, in the presence of oxygen (Taylor and Radda, 1971). Our results indicate that one or more Trp residues in the anti-FI,,-binding site are sensitive to photooxidation, explaining the large initial fluorescence decrease in the titration curve.…”

Section: Mapping Of the Antigen-binding Sitementioning

confidence: 60%

Regulation of the Flavin Redox Potential by Flavin‐Binding Antibodies

Bruggeman

Honegger

Kreuwel

et al. 1997

European Journal of Biochemistry

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Single-chain Fv antibody fragments binding different flavin forms [ 10-(5'-carboxybutyl-)flavin (Fl<,J and IO-(S'-carboxybutyl)-1,5-dihydroflavin (Fired)] have been generated from an antibody phage-display library to study how a protein environment regulates the redox potential, starting from a protein other than a natural flavoprotein. These 'flavobodies' are characterized by time-resolved and steady-state fluorescence spectroscopy, by competitive ELISA methods (mapping of the antigen-binding site), and by molecular modelling. The three-dimensional models of the antigen-binding sites are consistent with the experimental results. Binding of anti-Fl,,, 5 to flavin increases the redox potential, mainly due to an Arg residue interacting with the flavin N1. Thus anti-Fl,, 5 shows an 'oxidase-like' redox-potential behaviour, confirming the idea that positively charged residues in the vicinity of N1 increase the redox potential. The results obtained with anti-Fl,,, which do not resemble a natural flavoprotein, show that when the pyrimidine-like nucleus of the flavin is not involved in binding, the redox potential is not significantly affected. These results are in contrast to those obtained with chicken riboflavin-binding protein.Keywords: flavin; flavoprotein oxidase; antibody-binding domain ; modeling ; phage display.Flavin acts as cofactor in many redox enzymes and electrontransferring proteins. These flavin-containing enzymes catalyse a wide variety of biochemical reactions varying from oxidasetype to dehydrogenase-type and monooxygenase-type of reactions. This versatility sets flavoproteins apart from most other cofactor-dependent enzymes which, in general, only catalyse a single type of reaction (Ghisla and Massey, 1989). The redoxactive part of the flavin is the isoalloxazine ring, which can exist in oxidized flavoquinone, one-electron-reduced flavosemiquinone and two-electron-reduced flavohydroquinone states. The flavin redox potentials depend on the nature of the active site in which the flavin resides and vary largely among different flavoproteins (Stankovich, 1990). The role of the protein environment of the flavin cofactor in modulating the redox potential is still not properly understood. Here we have investigated the structural and redox properties of monoclonal antibodies elicited against oxidised and two-electron-reduced flavin and compared them with those of 'natural' flavoproteins.The isoalloxazine moiety of the flavin is amphipatic, consisting of a hydrophobic benzene-like part (ring A) and a hydrophilic pyrimidine moiety (ring C: Fig. 1). The N5 atom in ring B is electron deficient and is the site where the electrons enter the isoalloxazine (Platenkamp et al., 1987). The negative charge is spread over C4a, N5, N10 and N1 (Hall et al., 1987b). The degree to which this negative charge is stabilised or destabilised is an important factor governing the redox potential: a positive charge in the protein around ring C will contribute to increase the redox potential, whereas a negatively charged or hydro...

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“…Proteins are one of many biological molecules sensitive to photooxidation by flavins [11]. Upon photoactivation with visible light, flavins produce singlet oxygen

(^{1} O_{2})

and superoxide

,

two compounds with potent reactivity towards biomolecules [12].…”

Section: Resultsmentioning

confidence: 99%

Vitamin B₂‐mediated cellular photoinhibition of botulinum neurotoxin A

2005

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Botulinum neurotoxin (BoNT) is the most toxic species known to humans and has been identified as a potential bioterrorist threat. Unfortunately, the only existing countermeasures for BoNT intoxication involve vaccinations that are only effective prior to entry of the toxin into neuronal cells. Herein, we disclose the ability of the micronutrient riboflavin (vitamin B 2 ) to photooxidatively inactivate BoNT in cell-based assays without the need for toxin and riboflavin pre-exposure. In total, this study suggests that botulism neurotoxicity may be blunted with photodynamic therapy technology.

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[153] Flavins as photosensitizers

Cited by 19 publications

References 15 publications

Interactions of Flavins With Amino Acid Residues: Assessments From Spectral and Photochemical Studies

Interactions of Flavins With Amino Acid Residues: Assessments From Spectral and Photochemical Studies

Regulation of the Flavin Redox Potential by Flavin‐Binding Antibodies

Vitamin B₂‐mediated cellular photoinhibition of botulinum neurotoxin A

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[153] Flavins as photosensitizers

Cited by 19 publications

References 15 publications

Interactions of Flavins With Amino Acid Residues: Assessments From Spectral and Photochemical Studies

Interactions of Flavins With Amino Acid Residues: Assessments From Spectral and Photochemical Studies

Regulation of the Flavin Redox Potential by Flavin‐Binding Antibodies

Vitamin B2‐mediated cellular photoinhibition of botulinum neurotoxin A

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Vitamin B₂‐mediated cellular photoinhibition of botulinum neurotoxin A