Observation of 17O effects on MoV EPR spectra in sulfite oxidase; xanthine dehydrogenase, and MoO(SC6H5)4−

Cramer, Stephen P.; Johnson, Jean L.; Rajagopalan, K.V.; Sorrell, Thomas N.

doi:10.1016/0006-291x(79)91540-7

Cited by 45 publications

(56 citation statements)

References 10 publications

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“…Both the low- and the high-pH EPR signals of sulfite oxidase show strong coupling to a solvent-exchangeable oxygen when the sample is prepared in 17 O-labeled water, 296 although the nature of the coupling is distinct in each case. Initially ascribed to a terminal Mo=O group, subsequent resonance Raman work 297 has suggested that this coupling arises from the equatorial Mo–OH rather than apical Mo=O in the signal-giving Mo(V) species.…”

Section: The Sulfite Oxidase Familymentioning

confidence: 99%

The Mononuclear Molybdenum Enzymes

2014

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Section: The Sulfite Oxidase Familymentioning

confidence: 99%

The Mononuclear Molybdenum Enzymes

2014

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“…Pulsed EPR spectroscopies have been used to elucidate the structure of the Mo(V) forms, in order to provide unique insights into the catalytic mechanism at the Mo active site [36][37][38]64,74,75]. Comparative EPR studies on deuterated [63] and 17 O-enriched samples [76] can detect nearby protons and oxygen atoms in the intermediates, which are involved in SO catalysis. Pulsed EPR studies on the SO intermediates have been discussed in a recent review [40].…”

Section: Catalytic Mechanism Of Animal Somentioning

confidence: 99%

Sulfite-oxidizing enzymes

Kappler

Enemark

2014

J Biol Inorg Chem

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Sulfite oxidizing enzymes are essential mononuclear molybdenum (Mo) proteins involved in sulfur metabolism of animals, plants and bacteria. There are three such enzymes presently known: (1) sulfite oxidase (SO) in animals, (2) SO in plants, and (3) sulfite dehydrogenase (SDH) in bacteria. X-ray crystal structures of enzymes from all three sources (chicken SO, Arabidopsis thaliana SO, and Starkeya novella SDH) show nearly identical square pyramidal coordination around the Mo atom, even though the overall structures of the proteins and the presence of additional cofactors vary. This structural information provides a molecular basis for studying the role of specific amino acids in catalysis. Animal SO catalyzes the final step in the degradation of sulfur-containing amino acids and is critical in detoxifying excess sulfite. Human SO deficiency is a fatal genetic disorder that leads to early death, and impaired SO activity is implicated in sulfite neurotoxicity. Animal SO and bacterial SDH contain both Mo and heme domains, whereas plant SO only has the Mo domain. Intraprotein electron transfer (IET) between the Mo and Fe centers in animal SO and bacterial SDH is a key step in the catalysis, which can be studied by laser flash photolysis in the presence of deazariboflavin. IET studies on animal SO and bacterial SDH clearly demonstrate the similarities and differences between these two types of sulfite oxidizing enzymes. Conformational change is involved in the IET of animal SO, in which electrostatic interactions may play a major role in guiding the docking of the heme domain to the Mo domain prior to electron transfer. In contrast, IET measurements for SDH demonstrate that IET occurs directly through the protein medium, which is distinctly different from that in animal SO. Point mutations in human SO can result in significantly impaired IET or no IET, thus rationalizing their fatal effects. The recent developments in our understanding of sulfite oxidizing enzyme mechanisms that are driven by a combination of molecular biology, rapid kinetics, pulsed electron paramagnetic resonance (EPR), and computational techniques are the subject of this review.

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“…This hfi constant is significantly lower than the values for the lpH, hpH, and phosphate forms of wt chicken SO that have a hydroxyl ligand in the equatorial position. [40][41][42][43][44] The observation of the equatorial 17 O in the ESEEM spectra of Species 1 of 17 O-R160Q implies that both oxo ligands were exchanged with 17 O during incubation of the Mo(VI) form of the enzyme and before reduction with sulfite.…”

Section: Eseem Experiments With 17 O-enriched Samplesmentioning

confidence: 99%

Structural Studies of the Molybdenum Center of the Pathogenic R160Q Mutant of Human Sulfite Oxidase by Pulsed EPR Spectroscopy and ¹⁷O and ³³S Labeling

et al. 2008

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Electron paramagnetic resonance (EPR) investigation of the Mo(V) center of the pathogenic R160Q mutant of human sulfite oxidase (hSO) confirms the presence of three distinct species whose relative abundances depend upon pH. Species 1 is exclusively present at pH ≤ 6, and remains in significant amounts even at pH 8. Variable-frequency electron spin echo envelope modulation (ESEEM) studies of this species prepared with 33 S-labeled sulfite clearly show the presence of coordinated sulfate, as has previously been found for the "blocked" form of Arabidopsis thaliana at low pH (Astashkin, A. V.; Johnson-Winters, K.; Klein, E. L.; Byrne, R. S.; Hille, R.; Raitsimring, A. M.; Enemark, J. H. J. Am. Chem. Soc. 2007, 129, 14800). The ESEEM spectra of Species 1 prepared in 17 O-enriched water show both strongly and weakly magnetically coupled 17 O atoms that can be assigned to an equatorial sulfate ligand and the axial oxo ligand, respectively. The nuclear quadrupole interaction (nqi) of the axial oxo ligand is substantially stronger than those found for other oxo-Mo(V) centers studied previously. Additionally, pulsed electron-nuclear double resonance (ENDOR) measurements reveal a nearby weakly coupled exchangeable proton. The structure for Species 1 proposed from the pulsed EPR results using isotopic labeling is a six-coordinate Mo(V) center with an equatorial sulfate ligand that is hydrogen bonded to an exchangeable proton. Six-coordination is supported by the 17 O nqi parameters for the axial oxo group of the model compound, (dttd)Mo 17 O( 17 Otms), where H 2 dttd = 2,3:8,9-dibenzo-1,4,7,10-tetrathiadecane; tms = trimethylsilyl. Reduction of R160Q to Mo(V) with Ti(III) gives primarily Species 2, another low pH form, whereas reduction with sulfite at higher pH values gives a mixture of Species 1 and 2, as well as the "primary" high pH form of wild-type SO. The occurrence of significant amounts of the "sulfate-blocked" form of R160Q (Species 1) at physiological pH suggests that this species may be a contributing factor to the lethality of this mutation.

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Observation of 17O effects on MoV EPR spectra in sulfite oxidase; xanthine dehydrogenase, and MoO(SC6H5)4−

Cited by 45 publications

References 10 publications

The Mononuclear Molybdenum Enzymes

The Mononuclear Molybdenum Enzymes

Sulfite-oxidizing enzymes

Structural Studies of the Molybdenum Center of the Pathogenic R160Q Mutant of Human Sulfite Oxidase by Pulsed EPR Spectroscopy and ¹⁷O and ³³S Labeling

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Observation of 17O effects on MoV EPR spectra in sulfite oxidase; xanthine dehydrogenase, and MoO(SC6H5)4−

Cited by 45 publications

References 10 publications

The Mononuclear Molybdenum Enzymes

The Mononuclear Molybdenum Enzymes

Sulfite-oxidizing enzymes

Structural Studies of the Molybdenum Center of the Pathogenic R160Q Mutant of Human Sulfite Oxidase by Pulsed EPR Spectroscopy and 17O and 33S Labeling

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Structural Studies of the Molybdenum Center of the Pathogenic R160Q Mutant of Human Sulfite Oxidase by Pulsed EPR Spectroscopy and ¹⁷O and ³³S Labeling