<b>Photochemistry of Riboflavin. I. The Hydrogen Transfer Process in the Anaerobic Photobleaching of Flavins</b>

Moore, William M.; Spence, J. T.; Raymond, Floyd A.; Colson, Steven D.

doi:10.1021/ja00904a013

Cited by 84 publications

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“…The natural flavin (I) side chain (Rl0 = ribityl) has been changed into CH, in order to avoid photolytic side reactions [4]. The cyclic imide group in position 3 is alkylated throughout, which affords the desired high solubility in unpolar (R, = benzyl) and polar (R, = CH,COO-) environments or a t least sufficient solubility stretching out over a wide polarity range from water to toluene (R, = CH,).…”

Section: Methodsmentioning

confidence: 99%

Light‐Induced Alkylation and Dealkylation of the Flavin Nucleus

Walker

Hemmerich

Massey

1970

European Journal of Biochemistry

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The spectral course of irreversible photoreduction of the flavin nucleus by arylacetates and related compounds has been investigated in detail. The resulting benzylated dihydroflavins and their reoxidation products have been characterized spectrophotometrically, among them 5-benzylflavosemiquinone radical and 5-benzylflavoquinonium cation. Reversible and irreversible flavin reduction corresponding to hydride-or group-transfer from substrate to flavin are discussed with respect to their scope and limitations and possible biological implications in the action mechanism of flavin dependent dehydrogenases.Flavin sensitized photodecarboxylation of phenylacetate has been reported previously by our group [ 1,2] and was found to result in a new and irreversible type of flavin photoreduction, i . e. benzyl group transfer (rather than hydride or electron transfer) towards the acceptor positions 5 or 4a of the flavin nucleus (I). While "H-transfer" (the term "H-transfer" is meant formally regardless of the mechanism, i . e. hydride, H-atom or whatsoever), obtained for example with mandelic acid, is reversible under all conditions tested, the group-transfer reaction is I complicated by the fact that either product, 4a-benzyl-4a,5-dihydroflavin (11, "4a-~CH2FlredH") and 5-benz yl-1,Ei-dihydroflavin (111, "5-cpCH2F1,,dH"), can be isolated and has its own way of reoxidation with 0,, which is different from that of the unsubstituted Flr,aH, ("leucoflavin" or 1 ,5-dihydroflavin), the only dihydroflavin known before [3]. These pathways are illustrated in Scheme 1.This shows that also group transfer is reversible under certain conditions. The conditions imply action Trivial Names and Unusual Abbreviations. Flavin, 10-substituted 7,8-dimethyl-isoalloxazine ; lumiflavin, 7,8,10-trimethyl-isoalloxazine; Elox, flavin in the neutra!, oxidized state; Fl,,aH,, reduced flavin (dihydroflavin) ; HFI, flavosesemiquinone radical; pCH,, benzyl. of light for 4a-yCH,Flr,dH and of mild acid forIt is evident that, in order to interpret the structure and function of intermediates in flavin dependent biological oxidations, the physical properties of group transfer as well as H-transfer products and all possible types of reduced flavin should be characterized thoroughly. This alone might help to understand the reasons, originating from the substrate structure or environmental conditions, which switch the course of flavin dependent "substrate" oxidation from group towards H-transfer and vice versa. and polar (R, = CH,COO-) environments or a t least sufficient solubility stretching out over a wide polarity range from water to toluene (R, = CH,). 5-@3HzFlredH. MATERIALS AND METHODS AllAll other reagents were best grade from Fluka A. G. (Buchs, Switzerland), with the exception of tetraacetylisoriboflavin, obtained by reductive alloxane condensation (and subsequent acetylation in pyridine) of Z-phenylaz0-3,4-dimethyl-N-ribitylaniline, which in turn was a gift from HoffmannLa Roche.Optical spectra were run on Cary 14 instruments.The photochemical light sou...

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Section: Methodsmentioning

confidence: 99%

Light‐Induced Alkylation and Dealkylation of the Flavin Nucleus

Walker

Hemmerich

Massey

1970

European Journal of Biochemistry

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“…The photo-reduction of de-aerated riboflavin was studied in [21,22,25,28,[42][43][44]. It was proposed that water is the donor of hydrogen and that H 2 O 2 is generated by photo-excitation [42].…”

Section: Anaerobic Photo-reductionmentioning

confidence: 99%

“…Photo-activation of flavins in air-saturated solutions with reducing agents converts them during light exposure to the semi and fully reduced form, but then they get re-oxidized in the dark. Under anaerobic conditions stable photo-reduction to the fully reduced form is achieved [14,16,[20][21][22][23][24][25][26][27][28][29] even in the absence of exogenous reducing agents [22,24,29]. The involved mechanisms in the photo-reduction of flavins are discussed in [20][21][22][23][24][25][26][27][28][29][30][31][32].…”

Section: Introductionmentioning

confidence: 99%

“…Under anaerobic conditions stable photo-reduction to the fully reduced form is achieved [14,16,[20][21][22][23][24][25][26][27][28][29] even in the absence of exogenous reducing agents [22,24,29]. The involved mechanisms in the photo-reduction of flavins are discussed in [20][21][22][23][24][25][26][27][28][29][30][31][32]. It is generally accepted that the photo-excitation leads to triplet state population by intersystem crossing, and that the reduction occurs from the triplet state [21,22,[24][25][26][27][28][29][30][31][32].…”

Section: Introductionmentioning

confidence: 99%

“…The involved mechanisms in the photo-reduction of flavins are discussed in [20][21][22][23][24][25][26][27][28][29][30][31][32]. It is generally accepted that the photo-excitation leads to triplet state population by intersystem crossing, and that the reduction occurs from the triplet state [21,22,[24][25][26][27][28][29][30][31][32]. Some investigated reducing agents for photo-induced reduction of flavins are ethylene-diamine-tetraacetic acid (EDTA) [20,[22][23][24][27][28][29][30][31][32][33], nitrilotriacetate [20], phenylacetic acid [26], indole-acetic acid [26,28], ascorbic acid (vitamin C) [28], and tryptophan [28].…”

Section: Introductionmentioning

confidence: 99%

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Photo-induced reduction of flavin mononucleotide in aqueous solutions

2007

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Fortschritte in Chemie und Molekularbiologie der Flavine und Flavocoenzyme

1965

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Es wird versucht, aus neueren chemischen und biochemischen Daten eine Basis fur das Verstandnis Flavin-( Vitamin-B2-)abhangiger Oxydation aufzuzeigen. Diese Ubersicht mochte folgendes herausstellen: Die chemischen Eigenschaften der Flavine miissen nach Redoxstufen (Chinonstuje, Radikalstufe, Hydrochinonstuje) difSerenzievt werden, denn bei der Reduktion andern sich Planaritat, Energieinhalt der Tautomerjormen, Metall-Affinitat usw. drastisch. -Die Methylgruppe an C-8 der Flavochinone ist reaktionsfahig. -Die Elektronentransfer-Eigenschaften des Flavin-Systems hangen oft von der Kopplung an sekundare Redox-Systeme im Apoprotein ab. Diese Wechselwirkung Jtabilisiert die halbreduzierte Stufe des Flavins thermodynamisch. -Synthesen in der Dihydrostufe machen zahlreiche neue Flavin-Typen, u. a. stabilisierte jreie Radikale, zuganglich. -Das Flavinradikal reagiert nur Iangsam mit 0 2 , solange es nicht disproportionieren kann, d. h. die Jchnelle Flavin-Autoxydation verlauft iiber die Dihydrostufe. -Der Flavinkern gewinnt erst durch Aufnahme eines und nur eines Elektrons Affinitat zu Schwermetallionen. -Redox-Aktivitat und Kontakt mit dem Flavocoenzym sind fur die in Fiavoproteinen vorkommenden Metalle Fe und Mo sichergestellt. Die Eigenschaften der Metall-Koordinationssphare werden in erster Linie durch schwefelhaltige Gruppen des Apoproteins bestimmt I. Einleitung 1. Definition und Nomenklatur der Flavine Flavin ist die Trivialbezeichnung fur die chromophore, redox-aktive prosthetische Gruppe einer in Tier-und Pflanzenreich weit verbreiteten Klasse von Atmungs-Enzymen, der Flavoproteine. Die Flavin-Gruppe ist Teil einer nichtproteiden niedermolekularen Enzym-Untereinheit, des Flavocoenzyms, welches von Enzym[ l ] Vollstandige Erfassung der Literatur wird nicht angestrebt ; der Leser sei auf andere Darstellungen dieses Forschungsbereichs verwiesen, z. B. P. D . Boyer, H . Lardy u. K . Myrback: The Enzymes. Academic Press, New York-London, Bd. 11, 1960, S . 360, Bd. VII, 1963; V . Mussey u. C. Veeger, Annu. Rev. Biochem. 32, 553 (1963). zu Enzym sehr verschieden fest am ,,Apoprotein" haftet (vgl. Abschnitt V1,l). Die beiden Flavocoenzyme werden zu Unrecht als Flavin-Nucleotide bezeichnet (,,FMN" = Flavin-mono-nucleotid, ,,FAD" = Flavinadenin-dinucleotid, Schema I), denn das Flavin ist in den Flavocoenzymen nicht glykosidisch gebunden. Die saure Hydrolyse laBt daher den Polyhydroxy-Substituenten am Flavin-Kern intakt und fuhrt zum Riboflavin. Dieses alteste bekannte Flavin-Derivat ( Warburg und Christian 1932) [3] ging zunachst als Lactoflavin (Vitamin B2) in die Literatur ein. ~ [2] P . Hemmerich in : Mechanismen enzymatischer Reaktionen. 14. Mosbacher Colloquium der Ges. f. : Die Inaktivitat des auf Flavoprotein ubertragenen Wasserstoffs ist auffallend, da es sich urn eine Stickstoff-Acceptorfunktion (N-5) handeln muR. Es ist zu fragen, ob diese Inaktivitat des H-Atoms an N-5 durch das Enzymprotein bedingt oder aber eine Eigenschaft des freien reduzierten Coenzyms ist. Modellstudien hierzu werden vorbereitet. [7a] C. ...

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Photochemistry of Riboflavin. I. The Hydrogen Transfer Process in the Anaerobic Photobleaching of Flavins

Cited by 84 publications

References 0 publications

Light‐Induced Alkylation and Dealkylation of the Flavin Nucleus

Light‐Induced Alkylation and Dealkylation of the Flavin Nucleus

Photo-induced reduction of flavin mononucleotide in aqueous solutions

Fortschritte in Chemie und Molekularbiologie der Flavine und Flavocoenzyme

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