Room temperature hydrolysis of lumiflavin in alkaline aqueous solution

Photochemical regeneration of flavoenzymes - An Old Yellow Enzyme case-study

Direct, NAD(P)H-independent regeneration of Old Yellow Enzymes represents an interesting approach for simplified reaction schemes for the stereoselective reduction of conjugated C=C-double bonds. Simply by illuminating the reaction mixtures with blue light in the presence of sacrificial electron donors enables to circumvent the costly and unstable nicotinamide cofactors and a corresponding regeneration system. In the present study, we characterise the parameters determining the efficiency of this approach and outline the current limitations. Particularly, the photolability of the flavin photocatalyst and the (flavin-containing) biocatalyst represent the major limitation en route to preparative application.

Effect of alkali ions on optical properties of flavins: vibronic spectra of cryogenic M+lumiflavin complexes (M = Li–Cs)

Cryogenic ion spectroscopy of metal–lumiflavin (M⁺LF) complexes at the level of vibrational resolution illustrates the large impact of alkali ions on the optical properties of this prototypical flavin molecule.

Multicomponent spectrofluorimetric method for the assay of formylmethylflavin and its hydrolytic products: Kinetic applications

A multicomponent spectrofluorimetric method has been developed for the simultaneous assay of formylmethylflavin (FMF), an intermediate product in the photolysis of riboflavin (vitamin B₂), and its side-chain hydrolytic products, lumichrome (LC) in acidic solution and LC and lumiflavin (LF) in the alkaline solution as well as its ring cleavage products, 1,2-dihydro-1-methyl-2-keto-3-quinoxaline carboxylic acid (KA) and 1,2,3,4-tetrahydro-1-methyl-2,3-dioxo-quinoxaline (DQ) in alkaline solution. The assay method also takes into account an oxidation product of FMF, i.e. carboxymethylflavin (CMF), in both acid and alkaline solutions. The method involves adjustment of the pH of hydrolysed solution to 2.0 to convert FMF to its protonated form, extraction of LC (acid solution) or LC and LF (alkaline solution) with chloroform and their simultaneous assay by fluorescence measurement at 478 and 530 nm, respectively. The aqueous phase is readjusted to pH 6.5, extracted with chloroform to remove undegraded FMF and used for the assay of CMF, KA and DQ at 530, 443 and 420 nm, respectively. The chloroform extract is used for the assay of FMF at 530 nm. The proposed method has been validated and applied to the study of the kinetics of a hydrolysis reaction of FMF at pH 11.0. The calibration curves for FMF and degradation products are linear in the range of 0.1-1.0 × 10^-6 M. The limit of detection (LOD) and limit of quantification (LOQ) range from 2.54-5.75 × 10^-8 M and 0.78-1.74 × 10^-7 M, respectively, for these compounds. The mean recovery ranges from 99.3-102.1% with a RSD of 0.14-0.35%. Judging from the molar balance of FMF and the hydrolytic products, uniformity of analytical data during the reactions and linearity of kinetic plot, the method gives accurate results for the assay of FMF and all of its degradation products. It can be conveniently used for the assay of these compounds and for the kinetics and stability studies of FMF.

Multicomponent spectrofluorimetric method for the assay of carboxymethylflavin and its hydrolytic products: kinetic applications

The simultaneous assay of carboxymethylflavin (CMF), an intermediate in the photolysis of riboflavin, and its hydrolytic side-chain cleavage products, lumichrome (LC) (acid solution) and LC and lumiflavin (LF) as well as isoalloxazine ring cleavage products, 1,2-dihydro-1-methyl-2-keto-3-quinoxaline carboxylic acid (KA) and 1,2,3,4-tetrahydro-1-methyl-2,3-dioxo-quinoxaline (DQ) (alkaline solution) has been carried out by a multicomponent spectrofluorimetric method. The method is based on the adjustment of pH of the degraded solutions to 2.0 and extraction of LC and LF with chloroform. The chloroform extract is evaporated to dryness under reduced pressure, the residue dissolved in pH 6.5 citro-phosphate buffer and LC and LF determined at their fluorescence maxima at 478 and 530 nm, respectively. The pH of the aqueous phase is re-adjusted to 6.5 and the solution used for the determination of CMF, KA and DQ at the wavelengths of 530, 443 and 420 nm, respectively. The proposed method has been validated according to ICH guidelines. The calibration curves for CMF and its hydrolytic products are linear in the concentration range of 0.5-5.0 × 10^-6  M. The mean recovery ranges from 99.0-102.0% with relative standard deviation (RSD) of 0.19-0.99%. The limit of detection (LOD) and the limit of quantification (LOQ) are in the range of 1.17-1.78 × 10^-7  M and 3.55-5.40 × 10^-7  M, respectively. The uniformity of molar balance of CMF and degradation products during hydrolytic reactions indicates the accuracy of the proposed method for the spectrofluorimetric assay of the compounds. It has been applied to study the kinetics of hydrolytic reactions of CMF.

Photo-dynamics of photoactivated adenylyl cyclase TpPAC from the spirochete bacterium Turneriella parva strain H(T)

The photoactivated adenylyl cyclase TpPAC from the spirochete bacterium Turneriella parva was synthesized and the purified recombinant protein was characterized by biochemical and optical spectroscopic methods. TpPAC consists of a BLUF domain (BLUF = Blue Light sensor Using Flavin) and an adenylyl cyclase homology domain (CHD). A light induced cAMP cyclase activity of ≈ 53.3 nmolmg(-1)min(-1) was measured while in the dark the cyclase activity was approximately a factor of 240 lower. The photo-cycling dynamics of the BLUF domain of TpPAC was studied by absorption spectra, fluorescence quantum distribution, and fluorescence lifetime measurements. The quantum efficiency of BLUF domain signaling state formation was found to be ϕs ≈ 0.59. A three-component exponential recovery of the signaling state to the receptor state was observed with the time constants τrec,1 = 4.8s, τrec,2 = 34.2s, and τrec,3 = 293s at 21.3 °C. The protein thermal stability was studied by stepwise sample heating and cooling. An apparent TpPAC melting temperature of ϑm ≈ 46 °C was determined. The photo-degradation of TpPAC in the signaling state was studied by prolonged intense light exposure at 455 nm. An irreversible flavin photo-degradation was observed with quantum yield ϕD ≈ 8.7 × 10(-6).

Riboflavin interactions with oxygen-a survey from the photochemical perspective

In this short review we provide some insights to the main processes that riboflavin is involved in upon absorption of a photon. We describe riboflavin properties in its interactions with oxygen, comparing them to the properties of some other singlet oxygen sensitizers. Data are provided on riboflavin photosensitizing properties in vivo and in vitro, and its properties as an endogenous singlet oxygen sensitizer are discussed. We additionally report flavin catalytic role in organic synthesis and photochemical reactivity in solutions of riboflavin and some of its derivatives.

Photo, thermal and chemical degradation of riboflavin

Riboflavin (RF), also known as vitamin B2, belongs to the class of water-soluble vitamins and is widely present in a variety of food products. It is sensitive to light and high temperature, and therefore, needs a consideration of these factors for its stability in food products and pharmaceutical preparations. A number of other factors have also been identified that affect the stability of RF. These factors include radiation source, its intensity and wavelength, pH, presence of oxygen, buffer concentration and ionic strength, solvent polarity and viscosity, and use of stabilizers and complexing agents. A detailed review of the literature in this field has been made and all those factors that affect the photo, thermal and chemical degradation of RF have been discussed. RF undergoes degradation through several mechanisms and an understanding of the mode of photo- and thermal degradation of RF may help in the stabilization of the vitamin. A general scheme for the photodegradation of RF is presented.