Flavin adenine dinucleotide (FAD) is a cofactor for cytochrome-b5 reductase, the enzyme that maintains hemoglobin in its functional reduced state, and for glutathione reductase. This enzyme also protects erythrocytes from oxidative damage. FAD is a redox cofactor of several essential reactions in metabolism. This cofactor exists in two redox states, with FAD and FADH2 being the oxidized and reduced forms, respectively. FAD is formed of a riboflavin moiety (vitamin B2) coupled to a phosphate group of an ADP molecule. The reaction starts with the conversion of riboflavin into flavin mononucleotide catalyzed by riboflavin kinase. Flavin mononucleotide is subsequently transformed into FAD by adding an AMP moiety from ATP catalyzed by FAD-synthase. Therefore, FAD availability is tightly dependent on vitamin B2 and energy metabolism[1].
[1] Schnekenburger, M. and M. Diederich. “Nutritional Epigenetic Regulators in the Field of Cancer: New Avenues for Chemopreventive Approaches.”Epigenetic Cancer Therapy (2015): 393-425.
Labelled Flavine Adenine
xidase. Riboflavin kinase tumor necrosis factor receptor 1 NADPH oxidase
The prosthetic group of certain flavoproteins including D-amino acid oxidase, glucose oxidase, glycine oxidase, fumaric hydrogenase, histaminase, and xanthine oxidase. Riboflavin kinase tumor necrosis factor receptor 1 NADPH oxidase.
An adenine
nucleotide containing two phosphate groups esterified to the sugar moiety at the 5′-position.
Small quantities of FAD are purified by paper chromatography using tert-butyl alcohol/water, cutting out the main spot and eluting with water. Larger amounts can be precipitated from water as the uranyl complex by adding a slight excess of uranyl acetate to a solution at pH 6.0, dropwise and with gentle stirring. The solution is set aside overnight in the cold, and the precipitate is centrifuged off, washed with small portions of cold EtOH, then with cold peroxide-free diethyl ether. It is dried in the dark under vacuum over P2O5 at 50-60o. The uranyl complex is suspended in water, and, after adding sufficient 0.01M NaOH to adjust the pH to 7, the precipitate of uranyl hydroxide is removed by centrifugation [Huennekens & Felton Methods Enzymol 3 954 1957]. It can also be crystallised from water. It should be kept in the dark. More recently it was purified by elution from a DEAE-cellulose (Whatman DE 23) column with 0.1M phosphate buffer pH 7, and the purity was checked by TLC. [Holt & Cotton, J Am Chem Soc 109 1841 1987, Beilstein 26 III/IV 3632.]
