Flavin: Difference between revisions
imported>Pedro Silva (Experimental distinction of FAD from FMN) |
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[[Image:Riboflavin.png|thumb|Riboflavin]] | <!--[[Image:Riboflavin.png|thumb|Riboflavin]]--> | ||
'''Flavin''' is a [[Heterocycle|tricyclic heteronuclear organic ring]] based on [[pteridine]] whose 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 | '''Flavin''' is a [[Heterocycle|tricyclic heteronuclear organic ring]] based on [[pteridine]] whose biochemical source is the vitamin [[riboflavin]]. The flavin group is capable of undergoing oxidation-reduction reactions, and can accept either one electron in a two step process or can accept two electrons at once. 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]]. Since FMN fluoresces more than FAD, these flavins can be readily distinguished experimentally through a simple fluorescence-based assay. In this assay, the 530 nm fluorescence (upon a 360 nm excitation) of a sample solution is measured before and after treatment with [[Naja naja]] venom. Under these conditions the fluorescence of FMN solutions does not change, but the [[phosphodiesterase]]s present in the venom cleave FAD into FMN and adenine, yielding a 10-fold increase of fluorescence of FAD solutions [http://dx.doi.org/10.1016/0003-2697(75)90656-9]. | ||
==FAD== | ==FAD== | ||
'''Flavin adenine dinucleotide''' is a cofactor in the enzymes [[monoamine oxidase]], [[D-amino acid oxidase]], [[glucose oxidase]], and [[xanthine oxidase]]. | '''Flavin adenine dinucleotide''' is a cofactor in the enzymes [[monoamine oxidase]], [[D-amino acid oxidase]], [[glucose oxidase]], and [[xanthine oxidase]]. | ||
==FADH | ==FADH and FADH<sub>2</sub>== | ||
FADH and FADH<sub>2</sub> are (respectively) one-electron and two-electron [[redox|reduced]] forms of FAD. FADH<sub>2</sub> is | FADH and FADH<sub>2</sub> are (respectively) one-electron and two-electron [[redox|reduced]] forms of FAD. The redox potential (E<sup>0</sup>)of the FAD/FADH<sub>2</sub> pair is approximately 0 mV. It is used instead of [[NADH|NAD<sup>+</sup>]] (E<sup>0</sup>=-320 mV) as an electron acceptor in oxidation reactions with a [[reduction potential]] between approximately -300 mV and 0 mV. This occurs in some steps of the [[citric acid cycle]] and the [[beta-oxidation|&beta-oxidation] of fatty acids. Since the oxidized form (FAD) of the electron-carrier is a reactant in metabolism, it must be regenerated: this is accomplished by transferring the electrons carried by FADH<sub>2</sub> to a final electron acceptor. In [[aerobic respiration]], it donates its electrons to O<sub>2</sub> (through the mitochondrial [[electron transport chain]]), releasing enough energy to synthesize approximately 1.5 [[adenosine triphosphate|ATP]] per FADH<sub>2</sub>. | ||
==FMN== | ==FMN== | ||
'''Flavin mononucleotide''' is a [[prosthetic group]] found in [[NADH dehydrogenase]]. | '''Flavin mononucleotide''' is a [[prosthetic group]] found in [[NADH dehydrogenase]]. | ||
==See also== | ==See also== | ||
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==References== | ==References== | ||
* Voet, D.; Voet, J.G. (2004). ''Biochemistry'' (3rd ed.). John Wiley & Sons. ISBN 0-471-39223-5 | * Voet, D.; Voet, J.G. (2004). ''Biochemistry'' (3rd ed.). John Wiley & Sons. ISBN 0-471-39223-5 | ||
Latest revision as of 21:39, 6 April 2009
Flavin is a tricyclic heteronuclear organic ring based on pteridine whose biochemical source is the vitamin riboflavin. The flavin group is capable of undergoing oxidation-reduction reactions, and can accept either one electron in a two step process or can accept two electrons at once. 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. Since FMN fluoresces more than FAD, these flavins can be readily distinguished experimentally through a simple fluorescence-based assay. In this assay, the 530 nm fluorescence (upon a 360 nm excitation) of a sample solution is measured before and after treatment with Naja naja venom. Under these conditions the fluorescence of FMN solutions does not change, but the phosphodiesterases present in the venom cleave FAD into FMN and adenine, yielding a 10-fold increase of fluorescence of FAD solutions [1].
FAD
Flavin adenine dinucleotide is a cofactor in the enzymes monoamine oxidase, D-amino acid oxidase, glucose oxidase, and xanthine oxidase.
FADH and FADH2
FADH and FADH2 are (respectively) one-electron and two-electron reduced forms of FAD. The redox potential (E0)of the FAD/FADH2 pair is approximately 0 mV. It is used instead of NAD+ (E0=-320 mV) as an electron acceptor in oxidation reactions with a reduction potential between approximately -300 mV and 0 mV. This occurs in some steps of the citric acid cycle and the [[beta-oxidation|&beta-oxidation] of fatty acids. Since the oxidized form (FAD) of the electron-carrier is a reactant in metabolism, it must be regenerated: this is accomplished by transferring the electrons carried by FADH2 to a final electron acceptor. In aerobic respiration, it donates its electrons to O2 (through the mitochondrial electron transport chain), releasing enough energy to synthesize approximately 1.5 ATP per FADH2.
FMN
Flavin mononucleotide is a prosthetic group found in NADH dehydrogenase.
See also
References
- Voet, D.; Voet, J.G. (2004). Biochemistry (3rd ed.). John Wiley & Sons. ISBN 0-471-39223-5