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Applications of Enzymes in Amperometric Sensors: Problems and Possibilities
Published in Richard P. Buck, William E. Hatfield, Mirtha UmañA, Edmond F. Bowden, Biosensor Technology Fundamentals and Applications, 2017
An alternative approach which has also proved successful and applicable to a range of flavoproteins is the use of conducting organic salt electrodes for the oxidation of the reduced flavo-protein.30-34 For this application TTF.TCNQ, where TTF is tetrathiafulvalene, appears to be the best choice.30 TTF.TCNQ has been used with a range of flavoproteins including glucose oxidase, amino acid oxidases, xanthine oxidase and choline oxidase31,35Figure 6 shows a glucose membrane electrode based on TTF.TCNQ. Typical results for the detection of glucose are shown in Figure 7. Other flavoproteins can be used as shown by the results in Figure 8. Furthermore it is possible to dispense with the membrane and simply used enzyme directly adsorbed at the electrode surface. The response of these flavoprotein membrane electrodes can be analysed in terms of our published model36 to establish the rate limiting processes for each electrode. Such analyses show that in all cases, with the exception of the choline electrode, the response is determined by diffusion of the substrate through the dialysis membrane. This is a very satisfactory situation for an enzyme electrode since it means that the response is independent of the enzyme activity. In the case of the choline electrode we fine that the response is determined by both enzyme kinetics and diffusion. At present the precise mechanism of the oxidation of the reduced flavoprotein is the subject of some debate.16,33,37,38 Nevertheless electrodes of this type obviously work well and have been developed for in vivo applications,39,40Figure 9.
Fluorescence Lifetime Imaging Microscopy of Endogenous Biological Fluorescence
Published in Mary-Ann Mycek, Brian W. Pogue, Handbook of Biomedical Fluorescence, 2003
By comparison, FAD and FMN have typical lifetimes of ~4.7 and ~2.3 ns, and are strongly quenched upon protein binding for mean decay times ranging from 0.3 to 1 ns [2]. Flavins mainly exist as flavoproteins (FPs) in mitochondria, with lipoamide dehydrogenase and electron transfer flavoprotein being the major contributors to cellular flavin fluorescence [15,16].
Bioremediation of Cr(VI)-Contaminated Soil using Bacteria
Published in Maulin P. Shah, Removal of Refractory Pollutants from Wastewater Treatment Plants, 2021
Flavin mononucleotide (FMN) is a strong, often covalently bound, and is a part of flavoproteins. The oxidized flavin nucleotide [FMN(Ox.)] accepts one semiquinone-producing electron (a stable free radical) to form FMNH(Sq.).
Polarised fluorescence in FAD excited at 355 and 450 nm in water–propylene glycol solutions
Published in Molecular Physics, 2022
D. M. Beltukova, M. K. Danilova, I. A. Gradusov, V. P. Belik, I. V. Semenova, O. S. Vasyutinskii
The investigation of intracellular processes using time-resolved spectroscopy of endogenous fluorophores is currently one of the mainstreams in biological research. Nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) are important endogenous fluorophores that play an essential role in cellular respiration and are widely used as fluorescent biomarkers for investigation of metabolic processes in cells and tissues (see, e.g. review papers [1–3] and references therein). FAD is one of the most important cofactors that catalyses a number of one- and two-electron redox reactions as a component of flavoproteins and acts as a photoreceptor pigment. A wide variety of cellular processes utilise FAD: bioenergetics and metabolism, reactive oxygen species (ROS) production and defense against oxidative stress, cell differentiation, etc. In particular, disorders in FAD metabolism can lead to deficiencies of corresponding flavoproteins and cause a number of pathologies [4].
Multisubstrate specific flavin containing monooxygenase from Chlorella pyrenoidosa with potential application for phenolic wastewater remediation and biosensor application
Published in Environmental Technology, 2018
Flavoproteins are known to have a quite distinct UV-visible spectra [40]. The purified enzyme shows characteristic spectral properties of flavoproteins, with maxima around 271 nm, 345 nm (Fe-S clusters), 450 nm (flavins) and shoulder between 465–470 nm (Fe-S clusters) (Figure 4). This confirms the flavoprotein nature as predicted by peptide fragment spectra of the purified protein (Table 2). The presence of Fe-S clusters as denoted by the spectra is known for their role in oxidation reduction reactions. The presence of flavin and Fe-S cluster of the type [2Fe-2S] is important for functioning of aromatic hydroxylases. The Fe-S cluster may be present as a separate ferrodoxin or as part of an iron sulphur flavoprotein that interacts with NAD (P) directly [41]. The spectral characteristics of the purified enzyme is supported by similar spectral properties of phenol hydroxylase from fungal species as Candida tropicalis, Trichosporon cutaneum and bacterial species as Acinetobacter radioresistens, Pseudomonas pickettii [10,26,30,34].