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Pyranopterin dithiolene distortions relevant to electron transfer in xanthine oxidase/dehydrogenase.

Dong C, Yang J, Leimkühler S, Kirk ML - Inorg Chem (2014)

Bottom Line: The reducing substrates 4-thiolumazine and 2,4-dithiolumazine have been used to form Mo(IV)-product complexes with xanthine oxidase (XO) and xanthine dehydrogenase.The resonance Raman spectra reveal in-plane bending modes of the bound product and low-frequency molybdenum dithiolene and pyranopterin dithiolene vibrational modes.This work provides keen insight into the role of the pyranopterin dithiolene in electron-transfer reactivity.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Chemical Biology, The University of New Mexico , MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States.

ABSTRACT
The reducing substrates 4-thiolumazine and 2,4-dithiolumazine have been used to form Mo(IV)-product complexes with xanthine oxidase (XO) and xanthine dehydrogenase. These Mo(IV)-product complexes display an intense metal-to-ligand charge-transfer (MLCT) band in the near-infrared region of the spectrum. Optical pumping into this MLCT band yields resonance Raman spectra of the Mo site that are devoid of contributions from the highly absorbing FAD and 2Fe2S clusters in the protein. The resonance Raman spectra reveal in-plane bending modes of the bound product and low-frequency molybdenum dithiolene and pyranopterin dithiolene vibrational modes. This work provides keen insight into the role of the pyranopterin dithiolene in electron-transfer reactivity.

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Key vibrationalmodes computed for MoIV-4-TV: (A) productin-plane ring bending; (B) S–Mo–S symmetric core stretch;(C) dithiolene fold + Mo≡O rocking + pyranopterin ditholene.Other normal modes for MoIV-2,4-TV and MoIV-4-TVare in the SI.
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fig4: Key vibrationalmodes computed for MoIV-4-TV: (A) productin-plane ring bending; (B) S–Mo–S symmetric core stretch;(C) dithiolene fold + Mo≡O rocking + pyranopterin ditholene.Other normal modes for MoIV-2,4-TV and MoIV-4-TVare in the SI.

Mentions: Low-frequency rR spectra for reduced XOR and XDH product-boundspecies, collected on resonance with the MoIV-product MLCTband (780 nm excitation), are essentially identical (Figure 3). However, the spectra are dependent on the natureof the product molecule bound to molybdenum and display multiple resonantlyenhanced vibrations in the 200–600 cm–1 region.Beause the sulfur heteroatoms are part of the heterocyclic πsystem of the product and the mass of sulfur is approximately twicethat of oxygen, vibrations with appreciable product character will display frequency shifts relative to other resonantlyenhanced modes due to force constant and reduced mass changes. Thisheavy-atom-congener approach, coupled with vibrational-frequency calculations,represents a powerful method for the assignment of vibrational modesthat are localized on either the product half or the pyranopterinditholene half of the MoIV-product complex. Product-dependentspectral differences are clearly apparent at Raman shifts greaterthan ∼375 cm–1. The experimental dependenceof these vibrational bands on the nature of the product allows usto assign the MoIV-4-TV resonantly enhanced vibration at493 cm–1 (Figure 4A) andthe MoIV-2,4-TV enhanced vibrations at 411 and 513 cm–1 (Figure S2 in the SI)as in-plane product bending modes localized on the product.


Pyranopterin dithiolene distortions relevant to electron transfer in xanthine oxidase/dehydrogenase.

Dong C, Yang J, Leimkühler S, Kirk ML - Inorg Chem (2014)

Key vibrationalmodes computed for MoIV-4-TV: (A) productin-plane ring bending; (B) S–Mo–S symmetric core stretch;(C) dithiolene fold + Mo≡O rocking + pyranopterin ditholene.Other normal modes for MoIV-2,4-TV and MoIV-4-TVare in the SI.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4215880&req=5

fig4: Key vibrationalmodes computed for MoIV-4-TV: (A) productin-plane ring bending; (B) S–Mo–S symmetric core stretch;(C) dithiolene fold + Mo≡O rocking + pyranopterin ditholene.Other normal modes for MoIV-2,4-TV and MoIV-4-TVare in the SI.
Mentions: Low-frequency rR spectra for reduced XOR and XDH product-boundspecies, collected on resonance with the MoIV-product MLCTband (780 nm excitation), are essentially identical (Figure 3). However, the spectra are dependent on the natureof the product molecule bound to molybdenum and display multiple resonantlyenhanced vibrations in the 200–600 cm–1 region.Beause the sulfur heteroatoms are part of the heterocyclic πsystem of the product and the mass of sulfur is approximately twicethat of oxygen, vibrations with appreciable product character will display frequency shifts relative to other resonantlyenhanced modes due to force constant and reduced mass changes. Thisheavy-atom-congener approach, coupled with vibrational-frequency calculations,represents a powerful method for the assignment of vibrational modesthat are localized on either the product half or the pyranopterinditholene half of the MoIV-product complex. Product-dependentspectral differences are clearly apparent at Raman shifts greaterthan ∼375 cm–1. The experimental dependenceof these vibrational bands on the nature of the product allows usto assign the MoIV-4-TV resonantly enhanced vibration at493 cm–1 (Figure 4A) andthe MoIV-2,4-TV enhanced vibrations at 411 and 513 cm–1 (Figure S2 in the SI)as in-plane product bending modes localized on the product.

Bottom Line: The reducing substrates 4-thiolumazine and 2,4-dithiolumazine have been used to form Mo(IV)-product complexes with xanthine oxidase (XO) and xanthine dehydrogenase.The resonance Raman spectra reveal in-plane bending modes of the bound product and low-frequency molybdenum dithiolene and pyranopterin dithiolene vibrational modes.This work provides keen insight into the role of the pyranopterin dithiolene in electron-transfer reactivity.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry and Chemical Biology, The University of New Mexico , MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States.

ABSTRACT
The reducing substrates 4-thiolumazine and 2,4-dithiolumazine have been used to form Mo(IV)-product complexes with xanthine oxidase (XO) and xanthine dehydrogenase. These Mo(IV)-product complexes display an intense metal-to-ligand charge-transfer (MLCT) band in the near-infrared region of the spectrum. Optical pumping into this MLCT band yields resonance Raman spectra of the Mo site that are devoid of contributions from the highly absorbing FAD and 2Fe2S clusters in the protein. The resonance Raman spectra reveal in-plane bending modes of the bound product and low-frequency molybdenum dithiolene and pyranopterin dithiolene vibrational modes. This work provides keen insight into the role of the pyranopterin dithiolene in electron-transfer reactivity.

Show MeSH
Related in: MedlinePlus