Thermally Driven Intramolecular Charge Transfer in an Oxo-Molybdenum Dithiolate Complex

Me, Helton; Nl, Gebhart; Es, Davies; McMaster, Jonathan; Cd, Garner; Ml, Kirk

doi:10.1021/ja0100470

Cited by 40 publications

(42 citation statements)

References 32 publications

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“…Ϫ model compound, where on lowering the temperature below 250 K, the green-colored Mo(V) complex abstracts an electron from one of the dithiolene moieties, resulting in an orange Mo(IV) complex with a delocalized qdt⅐ radical (19). Such a formal electron transfer process is unlikely in the case of the enzyme, but it is possible that ambient thermal energy may be sufficient to disrupt binding of solvent to the wild-type reduced center at room temperature.…”

Section: Discussionmentioning

confidence: 99%

Spectroscopic and Kinetic Studies of Y114F and W116F Mutants of Me2SO Reductase from Rhodobacter capsulatus

Cobb

Hemann

Polsinelli

et al. 2007

Journal of Biological Chemistry

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Mutants of the active site residues Trp-116 and Tyr-114 of the molybdenum-containing Me 2 SO reductase from Rhodobacter capsulatus have been examined spectroscopically and kinetically. The Y114F mutant has an increased rate constant for oxygen atom transfer from Me 2 SO to reduced enzyme, the result of lower stability of the E red ⅐Me 2 SO complex. The absorption spectrum of this species (but not that of either oxidized or reduced enzyme) is significantly perturbed in the mutant relative to wildtype enzyme, consistent with Tyr-114 interacting with bound Me 2 SO. The as-isolated W116F mutant is only five-coordinate, with one of the two equivalents of the pyranopterin cofactor found in the enzyme dissociated from the molybdenum and replaced by a second MoAO group. Reduction of the mutant with sodium dithionite and reoxidation with Me 2 SO, however, regenerates the long-wavelength absorbance of functional enzyme, although the wavelength maximum is shifted to 670 nm from the 720 nm of wild-type enzyme. This "redoxcycled" mutant exhibits a Me 2 SO reducing activity and overall reaction mechanism similar to that of wild-type enzyme but rapidly reverts to the inactive five-coordinate form in the course of turnover.Dimethyl sulfoxide reductase catalyzes the reduction of dimethyl sulfoxide (Me 2 SO) to dimethyl sulfide (DMS) 3 and is a member of a large class of mononuclear molybdenum-containing enzymes (1-3) having an L 2 MoO(X) core (where L represents a pyranopterin cofactor coordinated to the molybdenum via an enedithiolate side chain, and X represents a ligand in most cases provided by the polypeptide, a serinate in the case of Me 2 SO reductase). Two forms of Me 2 SO reductase exist, as exemplified by the enzymes from Escherichia coli (a heterotrimer consisting of the DmsABC gene products) and Rhodobacter species (the monomeric DorA protein). Both are components of anaerobic respiratory chains and catalyze the reductive abstraction of oxygen from Me 2 SO according to the following stoichiometry using electrons derived from the respiratory pool.The Rhodobacter sphaeroides DorA enzyme is a soluble periplasmic protein of 85 kDa possessing the molybdenum cofactor as the sole redox-active center. Because of the distinctive absorption features of its molybdenum center, the DorA enzyme has become a paradigm for understanding the electronic structure of molybdenum centers of the L 2 MoO(X) variety (4 -12). In addition to steady-state kinetics under a variety of conditions, rapid reaction studies with both the Rhodobacter capsulatus (10) and R. sphaeroides enzyme (13) have also been reported. With the R. sphaeroides enzyme, the reaction of reduced enzyme with Me 2 SO at low pH is biphasic. A fast [Me 2 SO]-dependent phase (k lim ϳ 1000 s Ϫ1 ) yields a spectrally distinct E red ⅐Me 2 SO complex, with absorption maxima at 490 and 550 nm, followed by a slower oxygen abstraction step (35 s Ϫ1 ) that yields DMS and E ox (13). The hyperbolic dependence of the rapid phase on [Me 2 SO] gives a K d Me 2SO of ϳ155 M and indicates tha...

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Section: Discussionmentioning

confidence: 99%

Spectroscopic and Kinetic Studies of Y114F and W116F Mutants of Me2SO Reductase from Rhodobacter capsulatus

Cobb

Hemann

Polsinelli

et al. 2007

Journal of Biological Chemistry

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“…Furthermore, detailed electronic absorption, MCD, and EPR studies have been performed on related oxomolybdenum mono-dithiolene complexes, and the new studies reported herein provide a context in which to interpret the effects of a pterin substituent on the electronic structure of the coordinated dithiolene in the enzymes [15,[48][49][50][51][52][53].…”

Section: Spectroscopic Studiesmentioning

confidence: 99%

Synthesis, characterization, and spectroscopy of model molybdopterin complexes

Burgmayer

Kim

Petit

et al. 2007

Journal of Inorganic Biochemistry

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The preparation and characterization of new model complexes for the molybdenum cofactor are reported. The new models are distinctive for the inclusion of pterin-substituted dithiolene chelates and have the formulation Tp*MoX(pterin-R-dithiolene) (Tp* = tris(3,5,-dimethylpyrazolyl)borate), X= O, S, R= aryl or −C(OH)(CH 3 ) 2 ). Syntheses of Mo(4+) and (5+) complexes of two pterin-dithiolene derivatives as both oxo and sulfido compounds, and improved syntheses for pterinyl alkynes and [Et 4 N][Tp*Mo IV (S)S 4 ] reagents are described. Characterization methods include electrospray ionization mass spectrometry, electrochemistry, infrared spectroscopy, electron paramagnetic resonance and magnetic circular dichroism. Cyclic voltammetry reveals that the Mo(5+/4+) reduction potential is intermediate between that for dithiolene with electron-withdrawing substituents and simple dithiolate chelates. Electron paramagnetic resonance and magnetic circular dichroism of Mo(5+) complexes where X = O, R = aryl indicates that the molybdenum environment in the new models is electronically similar to that in Tp*MoO(benzenedithiolate).

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“…A considerable amount of experimental evidence over the last 40 years has pointed to the fact that dithiolenes are highly noninnocent ligands (20,86,110,113,(280)(281)(282). That is, they may be viewed in a valence bond description as existing somewhere between the extremes of neutral (dithione/dithiete) and dianionic (dithiolate) forms (Fig.…”

Section: Introductionmentioning

confidence: 99%