Molybdenum-containing Iron-Sulfur Flavoproteins

Enzymes containing the molybdenum (or tungsten) molybdopterin cofactor are found in eubacteria and archaebacteria and in lower and higher eukaryotes, 

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The CO dehydrogenase of the carboxidotrophic bacterium Oligotropha carboxidovorans is a molybdenum-containing iron-sulfur flavoprotein that catalyzes the oxidation of CO to CO2, generating a proton gradient across the cytoplasmic membrane (19, 20). 

XOD is one of the most complex flavoproteins and is composed of two identical and catalytically independent subunits each subunit contains one molybdenium center, two iron sulfur centers, and flavine adenine dinucleotide. The enzyme activity is due to a complicated interaction of FAD, molybdenium, iron, and labile sulfur moieties at or near the active site [260], It can be used to detect xanthine and hypoxanthine by immobilizing xanthine oxidase on a glassy carbon paste electrode [261], The elements are based on the chronoamperometric monitoring of the current that occurs due to the oxidation of the hydrogen peroxide which liberates during the enzymatic reaction. The biosensor showed linear dependence in the concentration range between 5.0 X 10 7 and 4.0 X 10-5M for xanthine and 2.0 X 10 5 and 8.0 X 10 5M for hypoxanthine, respectively. The detection limit values were estimated as 1.0 X 10 7 M for xanthine and 5.3 X 10-6M for hypoxanthine, respectively. Li used DNA to embed xanthine oxidase and obtained the electrochemical response of FAD and molybdenum center of xanthine oxidase [262], Moreover, the enzyme keeps its native catalytic activity to hypoxanthine in the DNA film. So the biosensor for hypoxanthine can be based on... 

Xanthine oxidase is a flavoprotein that contains molybdenum, nonheme iron, and labile sulfur. The enzyme is present in two forms, one with dehydrogenase activity (xanthine dehydrogenase) and the other with oxidase activity. The former is converted to the latter by oxidation of... 

Molybdenum hydroxylases (i.e., AO and XO) are flavoproteins that contain in addition to a FAD, a pterine cofactor coordinated to a molybdenum atom, and an iron sulfur center for their catalytic activity. They catalyze the two-electron oxidation of substrates with transfer to molecular oxygen to produce H2O2, and insert an atom of oxygen from water into a wide range of N-hctcrocycies and aldehydes via two-electron redox reaction as shown in equation 1.4 ... 

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