The prosthetic group associated with the Mo atom of the molybdenum cofactor found in all molybdenum-containing enzymes except nitrogenase. Many of the enzymes catalyze two-electron redox reactions that involve the net exchange of an oxygen atom between substrate and water. The molybdopterin prosthetic group contains a pterin ring bound to a dithiolene functional group on the 6-alkyl side chain. In bacterial enzymes a nucleotide is attached to the phosphate group. 
