Surface flavin adenine dinucleotide

Au NPs (1.2 nm) that include a single /V-hydroxysuccinimide-active ester functionality were modified with 2-amino-ethyl-flavin adenine dinucleotide, (5), and apo-glucose oxidase was reconstituted on the FAD cofactor units to yield the Au NP-GOx hybrid (Fig. 12.6a). The resulting hybrids were linked to the Au surface by different dithiol bridging units (8), (9), and (10). The resulting NP-functionalized glucose oxidase, GOx, exhibited electrical contact with the electrode surface, and the Au NPs... 

Amperometric biosensors based on flavin-containing enzymes have been studied for nearly 30 years. These sensors typically undergo several chemical or electrochemical steps which produce a measurable current that is related to the substrate concentration. In the initial step, the substrate converts the oxidized flavin adenine dinucleotide (FAD) center of the enzyme into its reduced form (FADH2). Because these redox centers are essentially electrically insulated within the enzyme molecule, direct electron transfer to the surface of a conventional electrode does not occur to a substantial degree. The classical" methods (1-4) of indirectly measuring the amount of reduced enzyme, and hence the amount of substrate present, rely on the natural enzymatic reaction ... 

Willner et al. [52] have created some elegant interfacial supramolecular assemblies to address this issue by removing the non-covalently bound flavin adenine dinucleotide (FAD) redox center from glucose oxidase and immobilizing the enzyme on a tether consisting of cystamine chemisorbed on a gold surface, a pyrroloquinoline quinone (PQQ) link and FAD. The mediator potential and electron transfer distances of this assembly were carefully chosen so that transfer of electrons from the FAD to the PQQ and to the electrode is very fast. A maximum rate of 900 150 s-1 for the enzymatic reaction within this monolayer assembly was obtained, which is indistinguishable from the value of about 1000 s-1 obtained for the enzyme in solution. While monolayers can offer molecular-level control of the interfacial structure, the... 

FAD (flavine adenine dinucleotide) is located at the enzyme s active site (as). In oxidizing glucose, the cofactor is reduced to FADH2, but the oxidized form of an appropriate mediator (Mox) has a redox potential sufficient to re-oxidize the cofactor whilst itself being reduced. In its simplest embodiment, the reduced mediator (Mred) diffuses from the active site at the enzyme to an electrode surface poised at a potential sufficiently oxidizing to re-oxidize the mediator ... 

The ability of these enzymes to contact directly the electrode is attributed to the peripheral location of the redox center. A detailed kinetic study [11] of the peroxidase-catalyzed reduction of H2O2 revealed that 42 % of the enzyme molecules are aligned on the electrode surface in a configuration where the redox heme site is accessible for direct electron transfer. Other enzymes possess two redox sites, and electron transfer proceeds vectorially from a peripheral site to an inner component. For example, /7-cresol methyl hydroxylase [PCMH, a flavin adenine dinucleotide (FAD)- and heme-containing redox enzyme] affects the direct oxidation of p-cresol to -hydroxybenzaldehyde [12[ ... 

Due to high biocompability and large surface are of cobalt oxide nanoparticles it can be used for immobilization of other biomolecules. Flavin adenine FAD is a flavoprotein coenzyme that plays an important biological role in many oxidoreductase processes and biochemical reactions. The immobilized FAD onto different electrode surfaces provides a basis for fabrication of sensors, biosensors, enzymatic reactors and biomedical devices. The electrocatalytic oxidation of NADH on the surface of graphite electrode modified with immobilization of FAD was investigated [276], Recently we used cyclic voltammetry as simple technique for cobalt-oxide nanoparticles formation and immobilization flavin adenine dinucleotide (FAD) [277], Repeated cyclic voltammograms of GC/ CoOx nanoparticles modified electrode in buffer solution containing FAD is shown in Fig.37A. 

ADP AFP ab as ALAT AP ASAT ATP BQ BSA CEH CK CME COD con A CV d D E E EC ECME EDTA EIA /e FAD FET FIA G GOD G6P-DH HBg HCG adenosine diphosphate a-fetoprotein antibody antigen alanine aminotranferase alkaline phosphatase aspartate aminotransferase adenosine triphosphate benzoquinone bovine serum albumin cholesterol ester hydrolase creatine kinase chemically modified electrode cholesterol oxidase concanavalin A coefficient of variation (relative standard deviation) layer thickness diffusion coefficient enzyme potential Enzyme Classification enzyme-chemically modified electrode ethylene diamine tetraacetic acid enzyme immunoassay enzyme loading factor flavin adenine dinucleotide field effect transistor flow injection analysis amplification factor glucose oxidase glucose-6-phosphate dehydrogenase hepatitis B surface antigen human chorionic gonadotropin... 

Catalysts played an important role in the emergence of life on Earth nearly 4 billion years ago. Catalysis by mineral surfaces and small molecules enabled the emergence of a proto-metabolic network that, in turn, enabled the emergence of the RNA world. The first macromolecular catalysts may have been ribozymes, an idea first proposed by Carl Woese that gained credence with the discovery of catalytic RNAs by Cech and Altman. Subsequently, ribozymes generated by in vitro evolution methods have been shown to catalyze a wide range of reactions involved in metabolism, including amino acid activation formation of coenzyme A (CoA), nicotinamide adenine dinucleotide (NAD), and flavin adenine dinucleotide (FAD)... 

Besides being used as adsorbent for gas molecules, both SWCNTs and MWC-NTs can be cast as a random network or a porous thin film on metal electrodes [57-59] or used as a three-dimensional scaffold [41,42] for biosensors. CNTs serve both as large immobilization matrices and as mediators to improve the electron transfer between the active enzyme site and the electrochemical transducer. Various enzymes, such as glucose oxidase and flavin adenine dinucleotide (FAD) can adsorb onto the CNT surface spontaneously and maintain their substrate-specific enzyme activity over prolonged times [57]. Recently, cells have been grown on CNT scaffolds which provide a three-dimensional permeable environment, simulating the natural extracellular matrix in a tissue [60-62]. 

Electrons and protons are donated to flavin adenine dinucleotide (FADH2) which exports the 2 protons the electrons are returned to the inner surface through iron-sulphur proteins (FeS). The electrons, together with 2 protons from the internal medium then reduce a single molecule of ubiquinone to hydroquinone (OH2), which diffuses across the membrane and releases protons outside. Finally, the electrons proceed through cytochromes b and o to water. 

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