Molybdopterin
Identifiers
CAS number	73508-07-3
PubChem	459
MeSH	molybdopterin
Properties
Molecular formula	C10H10N5O6PS2 + R groups
Molar mass	394.33 g/mol (R=H)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Some biosynthetic steps leading to molybdenum pterin, a molydopterin.

Molybdopterins when reacted with molybdenum or tungsten, are a class of cofactors found in most molybdenum (Mo) and all tungsten (W) enzymes. Synonyms for molydopterin are: MPT and pyranopterin-dithiolate.

Molydopterin consists of a pyranopterin, a complex heterocycle featuring a pyran fused to a pterin ring. In addition, the pyran ring features two thiolates, which serve as ligands in molybdo- and tungstoenzymes. In some cases, the alkyl phosphate group is replaced by an alkyl diphosphate nucleotide. Enzymes that contain the molybdopterin cofactor include xanthine oxidase, DMSO reductase, sulfite oxidase, and nitrate reductase. The only Mo-containing enzyme that does not feature this cofactor is nitrogenase. ^[1] The nomenclature for this biomolecule is potentially confusing: molybdopterin contains no molybdenum. When it it is complexed with molybdenum (molybdate), it is usually called molybdenum cofactor.

[edit] Biosynthesis

The biosynthesis of molybdopterin begins with guanosine triphosphate. Two enzymatic reactions convert this triphosphate to the cyclic phosphate of pyranopterin. One of these enzymes utilizes radical SAMs, often associated with C-X bond forming reactions. This intermediate pyranopterin is then converted to the molybdopterin via the action of three further enzymes. In this conversion the enedithiolate is formed, although the substituents on sulfur remain unknown. Sulfur is conveyed from cysteinyl persulfide in a manner reminiscent of the biosynthesis of iron-sulfur proteins. The monophosphate is adenylated (coupled to ADP) in a step that activates the cofactor toward binding Mo or W. These metals are imported as their oxyanions, molybdate and tungstate. Finally, Mo or W are inserted to give the molybdopterin cofactor. In some enzymes, such as xanthine oxidase, the metal is bound to one molybdopterin whereas in other enzymes, e.g. DMSO reductase, the metal is bound to two molybdopterin cofactors.^[2]

Models for the active sites of enzymes molybdopterin-containing enzymes are based on a class of ligands known as dithiolenes.^[3]

[edit] Molybdenum-containing enzymes which use molydopterin in either prosthetic group or cofactor

Cofactor of: ethylbenzene dehydrogenase, glyceraldehyde-3-phosphate ferredoxin oxidoreductase, respiratory arsenate reductase

Prosthetic Group of: formate dehydrogenase, purine hydroxylase, thiosulfate reductase

See ^[4]

[edit] References

1. ^ [1] Structure, synthesis, empirical formula for the di-sulfhydryl. Accessed Nov. 16, 2009.
2. ^ Schwarz, G. and Mendel, R. R. (2006). "Molybdenum cofactor biosynthesis and molybdenum enzymes". Annu. Rev. Plant Biol. 57: 623–647. doi:10.1146/annurev.arplant.57.032905.105437. 
3. ^ Kisker, C.; Schindelin, H.; Baas, D.; Rétey, J.; Meckenstock, R.U.; Kroneck, P.M.H. (1999). "A structural comparison of molybdenum cofactor-containing enzymes". FEMS Microbiol. Rev. 22: 503–521. doi:10.1111/j.1574-6976.1998.tb00384.x.  PubMed
4. ^ [2] Structure, synthesis, empirical formula for the di-sulfhydryl. Accessed Nov. 16, 2009.