Definitions

Flavin

Flavin

[fley-vin]
Flavin, Dan, 1933-96, American sculptor, b. New York City. In the early 1960s, Flavin experimented with fluorescent lights, bending them into complex, angular shapes. His sculptures, which are closely related to minimalism in underlying approach, incorporate installations of commercially made fixtures that diffuse colored light, thus breaking down or defining the space around them. Flavin's work is represented in many public collections, including the Solomon R. Guggenheim and Los Angeles County museums. Much of his late work was extremely large and site-specific. A gallery devoted to his work opened in Houston, Tex., in 1998 and features a large light frieze installed on its outer and inner surfaces. When Flavin died, he left instructions for the creation of his last work, a vast light construction, Untitled (Marfa Project), that was completed in 2001 and occupies six buildings at Donald Judd's huge Marfa, Tex., art space.

See studies by J. F. Ragheb, ed. (1999) and M. Govan et al. (2004).

flavin: see coenzyme.

Any of a class of organic compounds, pale yellow biological pigments that fluoresce green. They occur in compounds essential to life as coenzymes in metabolism. Plants and microbes can synthesize them, but animals must consume them in the diet. Riboflavin is the best-known flavin.

Learn more about flavin with a free trial on Britannica.com.

For the town in France, see Flavin, Aveyron.

Flavin (from Latin flavus, "yellow") is the common name for a group of organic compounds based on pteridine, formed by the tricyclic heteronuclear organic ring isoalloxazine. The biochemical source is the vitamin riboflavin. The flavin moiety is often attached with an adenosine diphosphate to form flavin adenine dinucleotide (FAD), and, in other circumstances, is found as flavin mononucleotide (or FMN), a phosphorylated form of riboflavin. It is in one or the other of these forms that flavin is present as a prosthetic group in flavoproteins.

The flavin group is capable of undergoing oxidation-reduction reactions, and can accept either one electron in a two-step process or two electrons at once. Reduction is made with the addition of hydrogen atoms to specific nitrogen atoms on the isoalloxazine ring system:

In aqueous solution, flavins are yellow-coloured when oxidized, taking a red colour in the semi-reduced anionic state or blue in the neutral (semiquinone) state, and colourless when totally reduced. The oxidized and reduced forms are in fast equilibrium with the semiquinone (radical) form, shifted against the formation of the radical:

Flox + FlredH2 ⇌ FlH

where Flox is the oxidized flavin, FlredH2 the reduced flavin (upon addition of two hydrogen atoms) and FlH the semiquinone form (addition of one hydrogen atom).

In the form of FADH2, it is one of the cofactors that can transfer electrons to the electron transfer chain.

Photoreduction

Both free and protein-bound flavins are photoreducible, that is, able to be reduced by light, in a mechanism mediated by several organic compounds, such as some aminoacids, carboxylic acids and amines.

FAD

Flavin adenine dinucleotide is a group bound to many enzymes including ferredoxin-NADP+ reductase, monoamine oxidase, D-amino acid oxidase, glucose oxidase, xanthine oxidase, and acyl CoA dehydrogenase.

FADH/FADH2

FADH and FADH2 are reduced forms of FAD. FADH2 is produced as a prosthetic group in succinate dehydrogenase, an enzyme involved in the citric acid cycle. In oxidative phosphorylation, two molecules of FADH2 typically yield 1.5 ATP each, or three ATP combined.

FMN

Flavin mononucleotide is a prosthetic group found in, among other proteins, NADH dehydrogenase, E.coli nitroreductase and old yellow enzyme.

Use as a dye

Flavin is the most important coloring matter obtained from quercitron (the bark of Quercus velutina, also called dyer's oak). Flavin is the commercial name for quercitron. Two preparations are "yellow flavin" and "red flavin," which contains only quercetin.

See also

References

  • Voet, D.; Voet, J.G. (2004). Biochemistry (3rd ed.). John Wiley & Sons. ISBN 0-471-39223-5

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