Flavin adenine dinucleotide adsorption

Flavin nucleotides—flavin adenine dinucleotide (FAD) and flavin mononucleotide (riboflavin-5 -phosphoric acid) (FMN)—as prosthetic groups can either comprise a metal or serve as cofactors without a metal. Electrochemical transformations of FAD and FMN are characterized by strong adsorption. The area occupied by a FAD molecule on a mercury electrode is 280 A, i.e., close to the geometrical dimensions corresponding to the molecular model. Reduction of FAD and FMN proceeds in two reversible... 

C,7H2oN406 376.368 Widely distributed, but occurs naturally in free form only in the retina, in whey and in urine. Main forms occurring in tissues and cells are flavine mononucleotide and flavine-adenine dinucleotide. Colour additive in food. Used as adsorption indicator in titrimetric detn. of Ag. Nutrient supplement. Vitamin cofactor. Orange needles. Sol. EtOH spar. sol. H2O. Mp 280° dec. [ ]d -9.8 (H2O). [ ]d -125 (20A NaOH). pAa, 1.9 pA,2 10.2 (25°). Green fluor. in soln. X ax 220 265 365 455 (H2O). 

The molecules of GO are denatured as a consequence of their adsorption on graphite electrodes from their more concentrated solutions. This denaturation results in a release of flavin adenine dinucleotide (FAD), which is directly adsorbed at the electrode. If the concentration of GO in the bulk of solution is low ( < 20 M) a significant fraction of molecules is adsorbed only weakly and remains in the native state so that their catalytic activity remains preserved [225]. If, under these conditions, glucose is present in the bulk of solution, it is possible to detect electron exchange between GO and the graphite electrode [225]. Similar results can be obtained at so-called organic salt electrodes (these electrodes are composed of the complex of tetrathiaful-valene and tetracyanoquinodimethane (TTF-TCNQ) [226]. 

The GOD content in tiiese modified enzymes were determined measuring the adsorption by flavin adenine dinucleotide in solutions of the lyophilized products (the solvents used were water and benzene for the PEG- and lipid-modified GOD, respectively) at 450 nm. The enzyme activities of the native and modified GOD s were measured by using a peroxidase/phenol/4-aminoantipynne chromogenic system. The solution (or dispersed medium in the case of the lipid-modified GOD) was 0.1 M potassium phosphate buffer (pH 7, 25°C). 

Since little is known about the interfacial behavior of enzymes other than glucose oxidase (GOD) at an electrode, Taniguchi et examined the electron-transfer reactions and adsorption behavior of several flavoen-zymes by fluorescence and SERRS measurements. They found that the intensities were useful in determining the location of flavin adenine dinucleotide (FAD) in the flavoenzymes, which suggested possible interfacial structures of these flavoenzymes. 

Goran, J. M., Mantilla, S. M., and Stevenson, K. J. 2013. Influence of surface adsorption on the interfacial electron transfer of flavin adenine dinucleotide and glucose oxidase at carbon nanotube and nitrogen-doped carbon nanotube electrodes. Anal. Chem. 85 1571-1581. 

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