Flavin adenine dinucleotide units

This thiol-disulfide interconversion is a key part of numerous biological processes. WeTJ see in Chapter 26, for instance, that disulfide formation is involved in defining the structure and three-dimensional conformations of proteins, where disulfide "bridges" often form cross-links between q steine amino acid units in the protein chains. Disulfide formation is also involved in the process by which cells protect themselves from oxidative degradation. A cellular component called glutathione removes potentially harmful oxidants and is itself oxidized to glutathione disulfide in the process. Reduction back to the thiol requires the coenzyme flavin adenine dinucleotide (reduced), abbreviated FADH2. 

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... 

Flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) are also carriers of electrons and have related chemical structures (Fig. 5). Both of these coenzymes consist of a flavine mononucleotide unit which contains the reactive... 

The molecule consists of a d-ribitol unit attached to an isoalloxazine ring (Figure 9-15). Anything more than a minor change in the molecule results in a loss of vitamin activity. Aqueous solutions of riboflavin are yellow with a yellowish-green fluorescence. The vitamin is a constituent of two coenzymes, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). FMN is... 

Nucleotides are stmctural units of deoxyribonucleic acid (DNA), ribonucleic acid (RNA) and cofactors such as coenzyme A (CoA), flavin adenine dinucleotide (FAD), nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), with important roles in energy transfer, metabolism and intracellular signalling. 

The inhibition of enzyme systems does not necessarily cause unwanted effects. Consider the enzyme xanthine oxidase. It contains two atoms of molybdenum, four FejSj, and two FAD (flavin adenine dinucleotide) moieties, and it has a molecular weight of 275,000-300.(X)0. There is no evidence that the two units (Mo/2Fe S2/F.AD) are near each other or interact m any way. It is believed that the immediate environment of each molybdenum atom consists of one oxygen and three sulfur atoms (additional ligands may be present) -... 

As a component of the coenz)une flavin adenine dinucleotide (FAD), riboflavin is essential for the energy-releasing reactions of the cell. The RDA for riboflavin is about 1.7 mg. Severe riboflavin deficiency is rare in most parts of the world, but a marginal deficiency of this vitamin is common even in the United States. Mild riboflavin deficiency leads to dry, cracked lips and other mild forms of dermatitis. In severe cases, however, riboflavin deficiency leads to extreme sensitivity to simlight and retarded growth in children. 

FIGURE 14.14 Structure of the oxidized form of flavin adenine dinucleotide (FAD). This electron carrier consists of a flavin mononucleotide (FMN) unit (shown in blue) and an AMP unit (shown in black). 

Nitrate reductase from higher plants is a tetramer with molecular weight of 160,000-500,000, with 0.04-0.06% of the Mo present as a prosthetic group (Notion and Hewitt, 1979 Hewitt and Notion, 1980). Each enzyme molecule has two flavine-adenine dinucleotides (FADs), two hemes, and one Mo atom. The nitrate reductases present in lower plants differ slightly in molecular weight, protein subunits, and number of flavine or heme units (Hewitt and Notion, 1980). 

Bioelectronics is another apphcation area, in which rotaxanes, particularly redox-active rotaxanes, could make a significant impact Enzyme electrodes are altered in these apphcations by direct electron transfer between the electrode surface and the redox enzyme. Electronic communication between the surface and the redox enzyme centers is hindered, because a separation exists. This impediment can be circumvented by aligning the enzyme with the electrode and utilizing the redox relay units as go-betweens. The aforementioned concept has been exploited to associate an apoprotein, apo-gjucose oxidase (apo-GOx), onto relay-functionalized materials including flavin adenine dinucleotide (FAD) monolayers, nanoparticles, and carbon nanotubes [85-88]. Katz etal. used reversible redox-active rotaxane shuttles in the bioelectrocatalyzed oxidation of glucose [80]. 

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