What is "molybdopterin"

n. (context biochemistry English) Any of a class of cofactors to several enzymes containing a pyranopterin coordinated to molybdenum

Molybdopterins 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 can be confusing: Molybdopterin per se contains no molybdenum; rather, this is the name of the ligand (a pterin) that will bind the active metal. After molydopterin is eventually complexed with molybdenum, the complete ligand 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 molybdenum-containing enzymes that do not feature molydopterins are the nitrogenases (enzymes that fix nitrogen). These contain an iron-sulfur center of a very different type, which also usually contains molybdenum. However, if molybdenum is present, it is directly bonded to other metal atoms.