Molybdenum Complexes of Reduced Pterins

Burgmayer, Sharon J. Nieter; Everett, Kenneth G.; Bostick, Laura

doi:10.1021/bk-1993-0535.ch008

Cited by 4 publications

(3 citation statements)

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“…Protein crystal structures suggest possible functions of MPT in Moco such as serving as an electron transfer conduit to FeS clusters which are hydrogen-bound directly to the pterin and creating a hydrogen-bonded anchor for the metal. − In addition, it has been suggested that pterin protonation may have a role in catalysis , and that the pterin oxidation state may tune the redox capabilities of the metal center. We have also demonstrated the affinity for Mo to coordinate directly to pterin in several oxidation states. , The likely noninnocence of MPT underscores the necessity of incorporating pterins or heteroaromatic substituents on dithiolenes in synthetic models . Most small molecule analogs for Moco have used simple aromatic systems to alleviate difficulties associated with pterin incorporation. , …”

Section: Introductionmentioning

confidence: 85%

“…We have also demonstrated the affinity for Mo to coordinate directly to pterin in several oxidation states. 17,18 The likely non-innocence of MPT underscores the necessity of incorporating pterins or heteroaromatic substituents on dithiolenes in synthetic models. 19 Most small molecule analogs for Moco have used simple aromatic systems to alleviate difficulties associated with pterin incorporation.…”

Section: Introductionmentioning

confidence: 99%

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Modeling Pyran Formation in the Molybdenum Cofactor: Protonation of Quinoxalyl–Dithiolene Promoting Pyran Cyclization

et al. 2019

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Mononuclear Mo and W enzymes require a unique ligand known as molybdopterin (MPT). This ligand binds the metal through a dithiolene chelate, and the dithiolene bridges a reduced pyranopterin group. Pyran scission and formation has been proposed as a reaction of the MPT ligand that may occur within the enzymes to adjust reactivity at the Mo atom. We address this issue by investigating oxo-Mo(IV) model complexes containing dithiolenes substituted by pterin or quinoxaline, and a hydroxyalkyl poised to form a pyran ring. hile the pterin-dithiolene model complex exhibits a low energy, eversible pyran cyclization, here we report that pyran cyclization does not spontaneously occur in the quinoxalyldithiolene model. However, protonating the quinoxalyl-dithiolene model induces pyran cyclization forming an unstable, pyrano-quinoxalyl-dithiolene complex which subsequently dehydrates and rearranges to a pyrrolo-quinoxlyl-dithiolene complex that was previously characterized. The protonated pyrano-quinoxalyl-dithiolene complex was characterized by absorption spectroscopy and cyclic voltammetry, and these results suggest pyran cyclization leads to a significant change in the Mo electronic structure exhibited as a strong ILCT transition and 370 mV positive shift of the Mo(V/IV) reduction potential. The influence of protonation on quinoxaline reactivity supports the hypothesis that the local protein environment in the second coordination sphere of Moco could control pyran cyclization. The results also demonstrate that the remarkable chemical reactivity of the pterin dithiolene ligand is subtlely distinct and not reproduced by the simpler quinoxaline analog that is often used to replace pterin in synthetic Moco models.

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Section: Introductionmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Modeling Pyran Formation in the Molybdenum Cofactor: Protonation of Quinoxalyl–Dithiolene Promoting Pyran Cyclization

et al. 2019

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“…Nevertheless, extrapolations from these model systems to molybdenum-containing enzymes were not satisfactory. Although the synthesis of such complexes of molybdenum coordinated to pterin species has deserved much attention [35] and has often been successful [68,82,89], the relationship to the reaction mechanism of molybdenum hydroxylases is not clear.…”

Section: Structure and Environment Of The Metal Centersmentioning

confidence: 99%

Structure and function of the xanthine-oxidase family of molybdenum enzymes

Romão

Huber

1998

Structure and Bonding

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This work gives an account of the recent achievements which have contributed towards the understanding of the structure and function of the xanthine oxidase family of enzymes-the molybdenum hydroxylases. It is based essentially on the crystallographic data of the aldehyde oxido-reductase from Desulfovibrio (D.) gigas, a member of that family, whose structure is described in detail. Comparisons are made, whenever appropriate, with spectroscopic, kinetic and model compound studies. Mechanistic implications of the crystal structure of the D. gigas enzyme are considered and extended to the xanthine oxidase family.

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Tungsten in biological systems

Kletzin

Adams

1996

FEMS Microbiology Reviews

134

144

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Tungsten (atomic number 74) and the chemically analogous and very similar metal molybdenum (atomic number 42) are minor yet equally abundant elements on this planet. The essential role of molybdenum in biology has been known for decades and molybdoenzymes are ubiquitous. Yet, it is only recently that a biological role for tungsten has been established in prokaryotes, although not as yet in eukaryotes. The best characterized organisms with regard to their metabolism of tungsten are certain species of hyperthermophilic archaea (Pyrococcus furiosus and Thermococcus litoralis), methanogens (Methanobacterium thermoautotrophicum and Mb. wolfei), Gram-positive bacteria (Clostridium thermoaceticum, C. formicoaceticum and Eubacterium acidaminophilum), Gram-negative anaerobes (Desulfovibrio gigas and Pelobacter acetylenicus) and Gram-negative aerobes (Methylobacterium sp. RXM). Of these, only the hyperthermophilic archaea appear to be obligately tungsten-dependent. Four different types of tungstoenzyme have been purified: formate dehydrogenase, formyl methanofuran dehydrogenase, acetylene hydratase, and a class of phylogenetically related oxidoreductases that catalyze the reversible oxidation of aldehydes. These are carboxylic reductase, and three ferredoxin-dependent oxidoreductases which oxidize various aldehydes, formaldehyde and glyceraldehyde 3-phosphate. All tungstoenzymes catalyze redox reactions of very low potential (< -420 mV) except one (acetylene hydratase) which catalyzes a hydration reaction. The tungsten in these enzymes is bound by a pterin moiety similar to that found in molybdoenzymes. The first crystal structure of a tungsten-or pterin-containing enzyme, that of aldehyde ferredoxin oxidoreductase from P. furiosus, has revealed a catalytic site with one W atom coordinated to two pterin molecules which are themselves bridged by a magnesium ion. The geochemical, ecological, biochemical and phylogenetic basis for W-vs. Mo-dependent organisms is discussed.

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Molybdenum Complexes of Reduced Pterins

Cited by 4 publications

References 0 publications

Modeling Pyran Formation in the Molybdenum Cofactor: Protonation of Quinoxalyl–Dithiolene Promoting Pyran Cyclization

Modeling Pyran Formation in the Molybdenum Cofactor: Protonation of Quinoxalyl–Dithiolene Promoting Pyran Cyclization

Structure and function of the xanthine-oxidase family of molybdenum enzymes

Tungsten in biological systems

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