Flavin adenine dinucleotide consists of two main portions: an adenine nucleotide and a phosphate containing riboflavin bridged together through their phosphate groups. Adenine is bound to a cyclic ribose at the 1' carbon, while phosphate is bound to the ribose at the 5' carbon to form the the adenine nucledotide. Riboflavin is formed by a carbon-nitrogen (C-N) bond between a isoalloxozine and a ribitol. The phosphate group is then bound to the on the terminal ribose carbon. Because the bond between the isoalloxozine and the ribitol is not considered to be a glycosidic bond, the riboflavin is not truly a nucleotide. [1] This makes the dinucleotide name misleading; however, the riboflavin group is still very close to a nucleotide in its structure.
FAD can be reduced to FADH2 through by the addition of two H+ and two e-. FADH2 can also be oxidized by the loss of one H+ and one e- to form FADH. The FAD form can be recreated from another loss on one H+ and one e-. FAD formation can also occur through the reduction and dehydration of flavin-N(5)-oxide.[2] Flavins take specific colors when in aqueous solution. FAD (fully oxidized) is yellow, FADH(half reduced) is either blue or red based on the pH, and the fully reduced form is colorless.[3] :
Changing the form can have a large impact on other chemical properties. For example, The fully oxidized form is subject to nucleophilic attack, the reduced form has high polarizability, while the half reduced form is unstable in aqueous solution.[4]
The spectroscopic properties of FAD and its variants allows for reaction monitoring by use of UV-VIS absorption and fluorescence spectroscopies. Each of the different forms of FAD have distinct absorbance spectra, making for easy observation of changes in oxidation state.[5] A major local maximum for FAD is observed at 450 nm, with an extinction coefficient of 11,300.[6] Flavins in general have fluorescent activity when unbound. This property can be utilized when examining protein binding.[7] Oxidized flavins have high absorbances of about 450 nm, and fluoresce at about 515-520 nm.[8]
- ^ Metzler DE, (2001) Biochemistry. The chemical reactions of living cells, 2nd edition, Harcourt, San Diego
- ^ Devlin, edited by Thomas M. (2011). Textbook of biochemistry : with clinical correlations (7th ed. ed.). Hoboken, NJ: John Wiley & Sons. ISBN 9780470281734.
{{cite book}}:|edition=has extra text (help);|first1=has generic name (help) - ^ Barile, M.; et al. (2013). "Biosynthesis of flavin cofactors in man;implications in health and disease". Current Pharmaceutical Design. 19 (14): 2649. doi:10.2174/1381612811319140014.
{{cite journal}}: Explicit use of et al. in:|last2=(help) - ^ Kim, H. J.; Winge, D. R. (2013). "Emerging Concepts in the Flavinylation of Succinate Dehydrogenase". Biochimica et Biophysica Acta. 1827 (5): 627–636. doi:10.1016/j.bbabio.2013.01.012.
- ^ Kim, H. J.; Winge, D. R. (2013). "Emerging Concepts in the Flavinylation of Succinate Dehydrogenase". Biochimica et Biophysica Acta. 1827 (5): 627–636. doi:10.1016/j.bbabio.2013.01.012.
- ^ Lewis, Jeffrey A.; Excalante-Semerena, Jorge C. (August 2006). "The FAD-Dependent Tricarballylate Dehydrogenase (TcuA) Enzyme of Salmonella enterica Converts Tricarballylate into cis-Aconitate". Journal of Bacteriology. 188 (15): 5479–5486.
{{cite journal}}: Cite has empty unknown parameter:|1=(help) - ^ Kim, H. J.; Winge, D. R. (2013). "Emerging Concepts in the Flavinylation of Succinate Dehydrogenase". Biochimica et Biophysica Acta. 1827 (5): 627–636. doi:10.1016/j.bbabio.2013.01.012.
- ^ Barile, M.; et al. (2013). "Biosynthesis of flavin cofactors in man;implications in health and disease". Current Pharmaceutical Design. 19 (14): 2649. doi:10.2174/1381612811319140014.
{{cite journal}}: Explicit use of et al. in:|last2=(help)