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PubMed2004

Liquid chromatographic analysis of riboflavin vitamers in foods using fluorescence detection.

The analysis of free riboflavin (RF) and its two coenzymes, flavin mononucleotide (FMN) and flavin-adenine dinucleotide (FAD), is optimized using reversed phase liquid chromatography with fluorescence detection. The stationary phase was amide-based and endcapped with trimethylsilyl, and the isocratic mobile phase consisted of a 10:90 v/v acetonitrile/phosphate buffer (pH 5). Peaks were identified by the retention characteristics and fluorescence spectra. Detection limits were 0.03, 0.05, and 0.24 ng for RF, FMN, and FAD, respectively. The vitamins were extracted using acetonitrile and the phosphate buffer. The procedure was applied to the determination of B2 vitamers in different types of food such as milk and soy-based infant formulas, beer, fruit juices, and honey of different types. Most B2 vitamin appeared as RF, while the coenzymes were present in lower amounts. The method was validated using two certified reference materials, and results within the certified range were obtained.

Chromatography, High Pressure Liquid↗
PubMed1983

Purification and properties of trimethylamine oxide reductase from Salmonella typhimurium.

The major inducible trimethylamine oxide reductase was purified from Salmonella typhimurium LT2. The molecular weights of the native enzyme were estimated to be 332,000 by gel filtration and 170,000 by nondenaturing disc gel electrophoresis. In sodium dodecyl sulfate-gel electrophoresis, the enzyme formed a single band of molecular weight 84,000. The isoelectric point was 4.28. Maximum activity was at pH 5.65 and 45 degrees C. Reduced flavin mononucleotide, but not reduced flavin adenine dinucleotide, served as an electron donor. The Km for trimethylamine oxide was 0.89 mM and Vmax was 1,450 U/mg of protein. The enzyme reduced chlorate with a Km of 2.2 mM and a Vmax of 350 U/mg of protein.

Chlorates↗
PubMedDate not supplied

Riboflavin as a source of autofluorescence in Eisenia fetida coelomocytes.

Immunocompetent cells of earthworms (coelomocytes) contain adherent amoebocytes and large eleocytes (chloragocytes); the latter are filled with numerous granules. We have previously shown that eleocytes of several (but not all) earthworm species exhibit strong autofluorescence detectable by fluorescent microscopy and flow cytometry. In the present article, the molecular origin of eleocytes autofluorescence was elucidated in coelomocytes expelled via dorsal pores in the integument of Eisenia fetida subjected to electric shock (1 min at 4.5 V). Spectrofluorometry (excitation and emission spectra and fluorescence lifetime), together with HPLC analysis of coelomocyte suspensions and supernatants, indicated that riboflavin but not FMN (flavin mononucleotide) or FAD (flavin-adenine dinucleotide) is the main fluorophore responsible for eleocyte fluorescence in this species. Additionally, lipofuscins are suspected to participate in this phenomenon.

Animals↗
PubMed1999

Catharanthine oxidation in flavin mononucleotide-mediated catharanthine-vindoline coupling reaction for synthesis of dimeric indole alkaloids under near-ultraviolet light.

A reaction model for the flavin mononucleotide-mediated coupling of catharanthine (C) and vindoline (V) under near-ultraviolet light was established based on the results of experiments on the effects of various physical and chemical factors on the disappearance of C and V, and the synthesis of the product, a dihydropyridinium intermediate (IM). The following events were deduced to occur. (i) C is oxidized in the presence of FMN and oxygen under near-ultraviolet light (C(OX1)). (ii) C(OX1) then couples with V to form IM. Degradation of C occurs simultaneously with its specific oxidation, as a result of which a part of the C is converted into the product (C*) which is incapable of coupling with V. When a reaction in which C(OX1) is further oxidized to another form (C(OX2)) is added and the counterpart for the coupling with V is changed to C(OX2) from C(OX1), the reaction model more appropriately describes the exponential increase in the product, IM, that occurs in the early stage of the coupling reaction. (iii) The degradation rate of IM is much greater after C has been consumed than before its disappearance. Using this reaction model, the coupling reactions under basal and optimized conditions were simulated and the results showed a good fit with the experimental values under both conditions. The kinetic study suggests that manganese ion (Mn2+) stimulates the binding of C(OX2) with V in addition to suppressing the degradation of C, resulting in an increased yield of IM. Mn2+ thus appears to be an important factor in the coupling reaction, in which it plays two different roles.

Journal Article↗
PubMedDate not supplied

[Effect of thiamine and riboflavin derivatives on the activity of xenobiotic-metabolizing enzyme and on the pharmacologic effect of analgesics].

Riboflavin deficiency decreases the activity of rat hepatic microsomal enzymes, addition of riboflavin and flavin mononucleotide stimulates their activity. At the same time thiamine deficiency induces xenobiotic metabolic enzymes and excessive addition of thiamine, thiamine diphosphate in particular, suppresses their activity. Flavin mononucleotide and thiamine diphosphate considerably modify the pharmacological effect of the agents which are actively metabolized by the hepatic microsomal system. Thiamine diphosphate enhances the pharmacological activities of orthophen, indomethacin, and tramal while flavin mononucleotide slightly diminishes them.

Animals↗
PubMed1987

A computer modelling approach to study the mode of binding of L-lyxoflavin-5'-monophosphate to flavodoxin.

The mode of binding of L-lyxoflavin-5'-monophosphate has been studied by a computer modelling method. Energetically preferred conformers of L-lyxoflavin-5'-monophosphate have been obtained using empirical potential energy functions. These minimum energy conformers were used to study the mode of their binding to flavodoxin. The study indicates that L-lyxoflavin-5'-monophosphate can also have coenzymatic activity similar to flavin mononucleotide. But its lower activity compared to flavin mononucleotide is due to the lower conformer population that initiates the binding process. It is also concluded from this study that the inability of L-lyxoflavin to promote growth in some cases is at the phosphorylation level and not at the coenzyme level.

Coenzymes↗
PubMed1982

Ferrisiderophore reductase activity in Agrobacterium tumefaciens.

Reduction of the iron in ferriagrobactin by the cytoplasmic fraction of Agrobacterium tumefaciens strictly required NaDH as the reductant. Addition of flavin mononucleotide and anaerobic conditions were necessary for the reaction; when added with flavin mononucleotide, magnesium was stimulatory. This ferrisiderophore reductase activity may be a part of the iron assimilation process in A. tumefaciens.

Anaerobiosis↗
PubMed1997

Resonance Raman study on the oxidized and anionic semiquinone forms of flavocytochrome b2 and L-lactate monooxygenase. Influence of the structure and environment of the isoalloxazine ring on the flavin function.

The oxidized and semiquinone anion radical forms of flavin mononucleotide carried by flavocytochrome b2 and L-lactate monooxygenase have been studied by resonance Raman (RR) spectroscopy. The RR spectra of their oxidized forms are compared with previously published RR data on various flavins and flavoproteins. Taking as a support available X-ray crystallographic data on flavoproteins, we have found correlations between the frequencies of RR bands II (1575-1588 cm-1), III (1534-1557 cm-1), and X (1244-1266 cm-1) and the H-bonding environment and/or the structure of the flavin ring. The present RR data provide strong evidence that the electron density, the conformation, and the H-bonding environment of the oxidized flavin mononucleotide of flavocytochrome b2 and L-lactate monooxygenase are different. As far as the anionic semiquinone form of flavoproteins is concerned, the behavior of two bands observed at 1280-1300 and 1320-1350 cm-1 suggests that they have vibrational origins similar to those of RR bands II and III of oxidized compounds. On this basis, the differences in conformation and H-bonding environment of the isoalloxazine ring, observed for the oxidized form of flavocytochrome b2 and L-lactate monooxygenase, appear to be preserved upon one-electron reduction of the flavin. For both flavoproteins, the RR spectra of the semiquinone form are affected by pyruvate binding. The data are interpreted in the frame of a change in H-bonding interaction of the C4&dbd;O carbonyl group of the flavin without significant alteration of the isoalloxazine conformation. This modification in electrostatic interaction quantitatively accounts for the pyruvate-induced changes of the oxidized/semiquinone and semiquinone/reduced redox potentials of the flavoproteins. Considering the high homology in the flavin catalytic sites of flavocytochrome b2 and L-lactate monooxygenase, the observed differences in H-bonding environment and conformation of the FMN ring are related to the different biological functions of the two flavoproteins.

Benzoquinones↗
PubMed1976

Synthesis, separation, identification and interconversion of riboflavin phosphates and their acetyl derivatives: a reinvestigation.

A reinvestigation of flavin phosphate synthesis, separation, identification, and interconversion was made in view of contradictory results in the literature. It has been confirmed that monochlorophosphoric acid is the best agent for selective 5'-monophosphorylation of riboflavin and derivatives. This reaction yields, however, invariably up to 20% of an isomer, which has been separated by preparative thick-layer chromatography and shown to be the 4'-monophosphate. All the earlier authors failed to detect this isomer which does not bind to flavodoxin. It equilibrates in dilute mineral acid to yield an 8:2 mixture of 5'-phosphate to 4'-phosphate by phosphate migration. The formation of 2',3',4'-triacetyl-flavin mononucleotide, according to Christie, S. M. H., Kenner, G. W. & Todd, A. R. (1954) J. Chem. Soc., 46-52, upon acid-catalysed acetylation of pure FMN, was confirmed. The same reaction under base catalysis, however, does not yield 2',3',4'-triacetyl-flavin mononucleotide as claimed by Khomutova, E. D., Shapiro, T. A., Mezentseva, M. W. & Berezovskii, V. M. (1965) Otd. Obshch. i. Tekhn. Khim., 241-244, Chem. Abstr. 65, 5516a, but in fact up to 80% 2', 3'-diacetyl-flavin 4':5'-cyclophosphate as the main product, which is stable under neutral and weak acidic conditions and does not hydrolyse to 2',3'-diacetyl-flavin 5'-monophosphate as claimed by McCormick, D.B. (1974) J. Heterocycl. Chem. 11, 969-974. The various flavin phosphates and their acetyl derivatives have been identified by pH-titration, electrophoresis, and proton magnetic resonance spectrometry, which direct analyses of crude reaction products as well as a rapid purity check of commerical FMN.

Acetylation↗
PubMed2004

The recognition of glycolate oxidase apoprotein with flavin analogs in higher plants.

The dependence of glycolate oxidase apoprotein (apoGO) activity on flavin analogs was surveyed in 9 higher plants from 7 families. Activities of all apoGOs depended not only on flavin mononucleotide (FMN) but also on flavin adenine dinucleotide (FAD), but not on riboflavin. The kinetic analysis showed that FMN was the optimum cofactor for apoGO from leaves of Brassica campestris. In plant kingdom, FMN, FAD and riboflavin are three flavin analogs with very similar structure, and they could coexist and be inter-converted from each other, so the question is how the apoprotein of glycolate oxidase (GO) recognized these flavin analogs. No inhibition effect of riboflavin on the activity of apoGO with FMN or FAD was found and no obvious quenching of riboflavin or apoGO protein fluorescence was detected with the addition of apoGO or riboflavin, respectively. These results indicated that riboflavin did not bind to apoGO tightly like FMN and FAD. Inorganic phosphate (Pi) did inhibit the activity of GO, and kinetic analysis revealed that this inhibition was caused by the competitive binding to apoGO between Pi and FMN. This competitive binding was further confirmed by the inhibition of Pi to the quenching of FMN and apoGO protein fluorescence with apoGO and FMN, respectively. It was suggested that the 5'-phosphate group of FMN or FAD may play a key role in the recognition and binding of riboflavin analog cofactors with apoGO.

Alcohol Oxidoreductases↗
PubMed1982

Properties of formate dehydrogenase in Methanobacterium formicicum.

Soluble formate dehydrogenase from Methanobacterium formicicum was purified 71-fold with a yield of 35%. Purification was performed anaerobically in the presence of 10 mM sodium azide which stabilized the enzyme. The purified enzyme reduced, with formate, 50 mumol of methyl viologen per min per mg of protein and 8.2 mumol of coenzyme F420 per min per mg of protein. The apparent Km for 7,8-didemethyl-8-hydroxy-5-deazariboflavin, a hydrolytic derivative of coenzyme F420, was 10-fold greater (63 microM) than for coenzyme F420 (6 microM). The purified enzyme also reduced flavin mononucleotide (Km = 13 microM) and flavin adenine dinucleotide (Km = 25 microM) with formate, but did not reduce NAD+ or NADP+. The reduction of NADP+ with formate required formate dehydrogenase, coenzyme F420, and coenzyme F420:NADP+ oxidoreductase. The formate dehydrogenase had an optimal pH of 7.9 when assayed with the physiological electron acceptor coenzyme F420. The optimal reaction rate occurred at 55 degrees C. The molecular weight was 288,000 as determined by gel filtration. The purified formate dehydrogenase was strongly inhibited by cyanide (Ki = 6 microM), azide (Ki = 39 microM), alpha,alpha-dipyridyl, and 1,10-phenanthroline. Denaturation of the purified formate dehydrogenase with sodium dodecyl sulfate under aerobic conditions revealed a fluorescent compound. Maximal excitation occurred at 385 nm, with minor peaks at 277 and 302 nm. Maximal fluorescence emission occurred at 455 nm.

Aldehyde Oxidoreductases↗
PubMed1978

Aldosterone stimulation of riboflavin incorporation into rat renal flavin coenzymes and the effect of inhibition by riboflavin analogues on sodium reabsorption.

This study was designed to investigate a possible relationship between the effect of aldosterone upon urinary electrolytes and the incorporation of [(14)C]riboflavin into renal [(14)C]flavin mononucleotide (FMN) and [(14)C]flavin adenine dinucleotide (FAD). Adrenalectomized Sprague-Dawley rats that weighed between 185 and 210 g were pretreated with 15 mug/100 g body wt dexamethasone intraperitoneally. 16 h later they were administered aldosterone (1.5 mug/100 g body wt) and [(14)C]riboflavin (5.0 muCi/200 g body wt). The urethra of each rat was ligated, and the rats were sacrificed by decapitation 3 h later. The urine was aspirated from the bladders of each rat and analyzed for total Na(+) and K(+) excretion while the kidneys were removed and the formation of [(14)C]FMN and [(14)C]FAD was determined for each kidney. There was a significant increase in the formation of renal [(14)C]FMN and [(14)C]FAD (27.3 and 14.4%, respectively) after aldosterone treatment. Aldosterone significantly decreased the excretion of Na(+) by 50%, and increased that of K(+) by 55%. To determine if the increased incorporation of [(14)C]riboflavin into renal [(14)C]FMN and [(14)C]FAD was an important intermediary step in the aldosterone-induced alterations in urinary Na(+) and K(+), the riboflavin analogues 7,8-dimethyl-10-formylmethyl isoalloxazine or 7,8-dimethyl-10-(2'-hydroxyethyl) isoalloxazine were given to the animals i.p. to diminish the conversion of riboflavin to FMN by competitively inhibiting the enzyme flavokinase (EC 2.7.1.26). These analogues were found to significantly counteract the decreased urinary excretion of Na(+) as a result of aldosterone from 26+/-9% to 124+/-58% (SEM) with a dose-related response when administered from 10 to 25 mug/100 g body wt. The same doses of the analogues that significantly increased the urinary output of Na(+) when administered simultaneously with aldosterone also significantly decreased the formation of renal [(14)C]FMN from 15+/-4 to 38+/-3% when compared with the effects of aldosterone alone. The analogues exerted no significant effect on the increased urinary excretion of K(+) by aldosterone. The analogues alone had no influence on urinary Na(+) and K(+) output or the formation of renal [(14)C]FMN and [(14)C]FAD at the dose levels that we investigated. These data strongly suggest that the enhanced synthesis of renal FMN and FAD may be a causative factor in the increased reabsorption of Na(+) as a result of aldosterone; and, consequently, riboflavin analogues may function as a novel class of antimineralocorticoids.

Aldosterone↗
PubMedDate not supplied

[Effect of the combined use of flavin coenzyme preparations and pyridoxine on the body vitamin balance in animals].

The effect of combined administration of flavin coenzymes and pyridoxine on B2-avitaminosis rats' supply with these vitamins has been studied. It has been disclosed that pyridoxine promotes more effective normalization of riboflavin and pyridoxine balance in the body, this balance being measured from the excretion of riboflavin and 4-pyridoxin acid with urine as well as from the content of total flavins in blood and tissues. In vitamin B2 lack, it is recommended that pyridoxin be combined with flavin mononucleotide and in particular with flavin adenine dinucleotide.

Animals↗
PubMed1975

Flavin nucleotides, glutathione reductase and assessment of riboflavin status.

The in vitro effects of flavin nucleotides on human erythrocyte glutathione reductase were studied. Flavin mononucleotide was found to be a potent inhibitor of glutathione reductase in haemolysates, having an effect at a concentration of 1 muM. Flavin adenine dinucleotide inhibited at a concentration at least ten fold this, lower levels producing the expected stimulation of enzyme activity. Different assay conditions also altered the activity of the enzyme, although the flavin mononucleotide inhibition remained. The implications of these findings in our understanding of glutatione reductase and in using the enzyme to assess riboflavin status are discussed.

Erythrocytes↗