FLUORESCENCE QUENCHING FOR FLAVINS INTERACTING WITH EGG WHITE RIBOFLAVIN-BINDING PROTEIN

Characterisation by Excitation-Emission Matrix Fluorescence Spectroscopy of Pigments in Mucus Secreted of Earthworm Eisenia foetida Exposed to Lead

The earthworm exposed to toxics shows physiological responses as: avoidance and mucus secretion. Heavy metals are particularly toxic to earthworms and the mucus secretion has been considered as a defence mechanism against undesirable substance. The chromophores present in the mucus secretion of Eisenia foetida have been poorly studied. Mucus secretion of E. foetida was induced by PbCl_2. High PbCl₂ concentrations provoked abundant mucus secretion which showed fluorescence when illuminated by UV light. Dialysis membrane separation, UV Visible and Excitation-Emission Matrix Fluorescence (EEM) spectroscopy were used to characterise the fluorescent pigments. EEM spectroscopy analysis of the mucus secretion signalled three excitation-emission peaks at: 310/380 nm, 370/520 nm and 440/520 nm. Two fluorophores were separated by dialysis. One of them matched the fluorescent compound riboflavin excitation-emission profile; the other is a protein with a peak 290/350 nm. Native-PAGE electrophoresis was conducted to assess the riboflavin-biding ability of the coelomic fluid protein produced by Eisenia foetida showing a high riboflavin-biding ability.

Design and characterization of 3-Azidothalidomide as a selective hydrogen sulfide probe

Hydrogen sulfide (H2S) has been recently recognized as an important signaling molecule in biological systems. Herein, we report the development of a fluorescence turn-on probe based on the structure of pomalidomide, a FDA approved drug for the treatment of multiple myeloma. Various characterizations demonstrated high selectivity and sensitivity of this probe towards H2S. Furthermore, the application of this probe to detect H2S in living cells was confirmed by flow cytometry and fluorescence imaging studies.

Fluorescence of bioaerosols: mathematical model including primary fluorescing and absorbing molecules in bacteria

This paper describes a mathematical model of fluorescent biological particles composed of bacteria, viruses, or proteins. The fluorescent and/or light absorbing molecules included in the model are amino acids (tryptophan, etc.); nucleic acids (DNA, RNA, etc.); coenzymes (nicotinamide adenine dinucleotides, flavins, and vitamins B₆ and K and variants of these); and dipicolinates. The concentrations, absorptivities, and fluorescence quantum yields are estimated from the literature, often with large uncertainties. The bioparticles in the model are spherical and homogeneous. Calculated fluorescence cross sections for particles excited at 266, 280, and 355 nm are compared with measured values from the literature for several bacteria, bacterial spores and albumins. The calculated 266- and 280-nm excited fluorescence is within a factor of 3.2 of the measurements for the vegetative cells and proteins, but overestimates the fluorescence of spores by a factor of 10 or more. This is the first reported modeling of the fluorescence of bioaerosols in which the primary fluorophores and absorbing molecules are included.

Review - Flavins as photoreceptors of blue light and their spectroscopic properties

This review describes 1) the development of studies on flavin photoreceptors as blue light photoreceptors in many living organisms: their kinds and functions; 2) the studies on spectroscopic properties of flavins, both their dimers and monomers; 3) nonradiative excitation energy transport in the presence of monomers and fluorescent/nonflurescent FMN dimers (excitation traps). The existence equilibrated luminescent FMN centers, energy migration and excitation sink to FMN dimers are taken into account.

Electrochemistry of riboflavin-binding protein and its interaction with riboflavin

Riboflavin-binding protein (RBP, a carrier of riboflavin) plays an essential role in embryo development. Electrochemical studies of the riboflavin-RBP interactions have been so far limited to changes in polarographic and voltammetric responses of riboflavin because of lack of methods capable to detect electrochemical changes in the RBP responses. Here we used constant current chronopotentiometric stripping analysis (CPSA) with the hanging mercury drop electrode (HMDE) and square wave voltammetry (SWV) with carbon paste electrode (CPE) to investigate RBP. We found that CPSA of RBP produces electrocatalytic peak H, capable to discriminate between apoprotein and holoprotein forms of RBP. This peak is suitable for studies of RBP-riboflavin interaction at nanomolar concentrations. We observed no sign of a release of riboflavin from holoprotein adsorbed at the HMDE surface. SWV at CPE required higher concentrations of RBP and displayed almost identical oxidation peaks of apoprotein and holoprotein.

Stability and conformation of the complexes of riboflavin with aromatic hydroxy compounds in an aqueous medium

Overall equilibrium constants K' for the formation of molecular complexes of riboflavin with the conjugate forms of different aromatic hydroxy compounds are greater in magnitude than those involving the protonated forms of the hydroxy compounds. There is good agreement between the K(B) values determined by using absorption and emission methods. Based on the magnitude of K(B), it is possible to differentiate between the donor capacities of the hydroxy compounds in the charge transfer complexes with riboflavin. Molecular modeling studies indicate stacking interactions for all the systems in an aqueous medium.

Studies on the riboflavin-resorcinol interaction in an aqueous medium and its pH dependence

The equilibrium constants, K', for the formation of the molecular association complex between riboflavin and resorcinol in the pH range 6-8 were found to be in the range 5-25 mol(-1)dm(3) by difference absorption spectroscopy. The equilibrium constants from emission spectroscopy were estimated to be in the range 38-55 mol(-1)dm(3) over the same pH range. Both sets of K' show a remarkable dependence on pH. The equilibrium constants K(A) and K(B) describing the interaction of riboflavin with neutral and ionic forms of resorcinol, respectively, obtained by resolving K', shows that K(B) is much greater than K(A). Molecular modeling studies suggest a stacked conformation of the two components in the complexed form. The interaction energies obtained from modeling studies also suggest a stronger interaction between the ionic form of resorcinol and riboflavin.

Interactions of flavins with melanin. Studies on equilibrium binding of riboflavin to dopa-melanin and some spectroscopic characteristics of flavin-melanin complex

Natural melanins are photoprotective pigments that in mammals are principally found in the skin, hair, and eyes. Although the molecular mechanism of photoprotection of pigmented cells has not yet been established, several hypotheses have been proposed with melanin acting as a light filter, free radical scavenger, and quencher of electronically excited states of reactive intermediates. It can be expected that the detoxicating efficiency of melanin should be enhanced if the melanin and potentially cytotoxic species are brought close together. Such a situation may occur for a number of photosensitizing dyes that have the ability to bind to melanin. The interaction of melanin with flavins has been studied under strictly controlled experimental conditions. The equilibrium dialysis method has been employed to determine dissociation constants and the number of binding sites in melanin at pH 5-9. The data reveal that synthetic DOPA-melanin has two different classes of binding sites with dissociation constants of 10(-6) and 10(-5) M, respectively. The overall binding capacity of melanin, at pH 7, is 250 nmol RF/mg melanin. The amount of bound-to-melanin RF increases with pH. The absorption spectra of melanin complexes with RF and lumiflavin indicate that hydrophobic interaction may be involved in the binding of these flavins by melanin. No changes in flavin fluorescence have been detected after binding of flavin to melanin. It appears that, contrary to cationic photosensitizing dyes, the singlet excited state of flavin molecules is not quenched by melanin.