| Molybdopterin | |
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| 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 | |
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. 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.
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]
Contents |
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]
Selenium-containing version, and ability to bind active tungsten
Tungsten has not been found to be necessary or used in eukaryotes, but it is an essential nutrient for some bacteria. For example, enzymes called oxidoreductases use tungsten similarly to molybdenum by using it in a tungsten-pterin complex with molybdopterin. Thus, molybdopterin may complex with either molybdenum or tungsten in use by bacteria. Tungsten-using enzymes typically reduce free carboxylic acids to aldehydes.[4] The first tungsten-requiring enzyme to be discovered also requires selenium, and in this case the tungsten-selenium pair may function analogously to the molybdenum-sulfur pairing of some molybdenum cofactor requiring enzymes.[5] One of the enzymes in the oxidoreductase family which sometimes employ tungsten (bacterial formate dehydrogenate H) is known to use a selenium-molybdenum version of molybdopterin.[6] Although a tungsten-containing xanthine dehydrogenase from bacteria has been found to contain tungsten-molydopterin and also non-protein bound selenium, a tungsten-selenium molybdopterin complex has not been definitively described.[7]
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 [8]
References
- ^ [1] Structure, synthesis, empirical formula for the di-sulfhydryl. Accessed Nov. 16, 2009.
- ^ Schwarz, G. and Mendel, R. R. (2006). "Molybdenum cofactor biosynthesis and molybdenum enzymes". Annu. Rev. Plant Biol. 57: 623–647. doi:.
- ^ 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:. PubMed
- ^ Lassner, Erik (1999). Tungsten: Properties, Chemistry, Technology of the Element, Alloys and Chemical Compounds. Springer. pp. 409–411. ISBN 0306450534. http://books.google.com/books?id=foLRISkt9gcC&pg=PA409&lpg=PA409&dq=tungsten+nutrient+organisms&source=web&ots=-rtHF9sWBY&sig=CoCD7Wp0HS-QRzQEoiPCisLaP04&hl=en&sa=X&oi=book_result&resnum=1&ct=result.
- ^ Stiefel, E. I. (1998). "Transition metal sulfur chemistry and its relevance to molybdenum and tungsten enzymes". Pure & Appl. Chem. 70 (4): 889–896. doi:. http://media.iupac.org/publications/pac/1998/pdf/7004x0889.pdf.
- ^ Khangulov, S. V. et al. (1998). "Selenium-Containing Formate Dehydrogenase H from Escherichia coli: A Molybdopterin Enzyme That Catalyzes Formate Oxidation without Oxygen Transfer". Biochemistry 37: 3518–3528. doi:.
- ^ Eur J Biochem 1999 Sep;264(3):862-71
- ^ [2] Structure, synthesis, empirical formula for the di-sulfhydryl. Accessed Nov. 16, 2009.
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