Electron paramagnetic resonance studies on the molybdenum center of assimilatory NADH:nitrate reductase from Chlorella vulgaris.

Solomonson, Larry P.; Barber, Michael J.; Howard, William D.; Johnson, Jean L.; Rajagopalan, K.V.

doi:10.1016/s0021-9258(17)43534-4

Cited by 46 publications

(23 citation statements)

References 24 publications

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“…The EPR properties of the molybdenum center of nitrate reductase from Chlorella vulgaris , and Candida nitratophila , as well as spinach, have been reported and while there is a substantial degree of similarity between these enzymes and sulfite oxidase, there are also significant differences as well. There is evidence for “high-pH” and “low-pH” signals from all three nitrate reductases, analogous to the signals seen with sulfite oxidase, with the “low-pH” signals exhibiting coupling to a single solvent-exchangeable proton.…”

Section: B the Assimilatory Nitrate Reductasesmentioning

confidence: 99%

The Mononuclear Molybdenum Enzymes

1996

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Section: B the Assimilatory Nitrate Reductasesmentioning

confidence: 99%

The Mononuclear Molybdenum Enzymes

1996

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“…A number of these signals have been characterized in terms of g values and hyperfine couplings to nuclei of nonzero spin. 6, [15][16][17][18][19][20][21][22][23][24] In several of these systems, anomalously high g values (g | > g e ) and/or an "inverted" trend in g values (g | > g ⊥ ) have been noted. Previous studies [25][26][27][28][29][30][31][32][33][34] of relatively simple molybdenum(V) oxyhalide anions have attributed such anomalies to various combinations of three effects: (1) large metal-ligand covalencies, (2) large values S0020-1669(96)01097-X CCC: $14.00 © 1997 American Chemical Society of ligand spin-orbit coupling, and (3) the influence of lowenergy charge transfer states.…”

Section: Introductionmentioning

confidence: 98%

“…Partial reduction of native enzymes or treatment of the enzymes with some inhibitors produces Mo(V) species which give EPR signals in the g ≈ 2 region. A number of these signals have been characterized in terms of g values and hyperfine couplings to nuclei of nonzero spin. ,− In several of these systems, anomalously high g values ( g ∥ > g e ) and/or an “inverted” trend in g values ( g ∥ > g ⊥ ) have been noted. Previous studies − of relatively simple molybdenum(V) oxyhalide anions have attributed such anomalies to various combinations of three effects: (1) large metal−ligand covalencies, (2) large values of ligand spin−orbit coupling, and (3) the influence of low-energy charge transfer states.…”

Section: Introductionmentioning

confidence: 99%

Density Functional Calculations ofgValues and Molybdenum Hyperfine Coupling Constants for a Series of Molybdenum(V) Oxyhalide Anions

and

Westmoreland

1997

Inorg. Chem.

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The electronic structures of the ions [MoOCl4]-, [MoOF5]2-, [MoOCl4(H2O)]-, and [MoOBr4(H2O)]- have been calculated by spin-polarized density functional calculations. The results confirm and extend previous calculations on these ions. In addition, the output eigenfunctions and eigenvalues have been used to calculate g values and molybdenum hyperfine coupling constants. The results reproduce the trends in the experimental parameters well but tend to overestimate the magnitudes of both the g values and the hyperfine coupling constants. It is shown from the calculated EPR parameters that the contributions of low-energy charge transfer states and the covalencies of the ground and excited states are the major contributors to deviations of g values from the spin-only value. Ligand-based spin−orbit coupling becomes important with increasing atomic number for the halides but never dominates. The molybdenum hyperfine couplings are dominated by Fermi contact terms which, in turn, originate primarily from spin polarization of the core 4s electrons. A comparison of [MoOCl4]- with [MoOCl4(H2O)]- indicates that the changes in EPR parameters observed on adding a sixth ligand to the coordination sphere arise from electronic structural changes due to geometrical distortions and not to specific electronic contributions from the added ligand.

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“…Other significant differences between the two enzymes include a tyrosine residue close to molybdenum in sulfite oxidase (Tyr 322), which is an asparagine (Asn 336) in nitrate reductase. This tyrosine residue has been suggested as a candidate for that controlling the transition between high-pH and low-pH Mo(V) sulfite oxidase; , however, the observation of analogous Mo(V) EPR signals in Chlorella nitrate reductase argues against this …”

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confidence: 99%