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The state of reduction of molybdopterin in xanthine oxidase and sulfite oxidase.

Publication ,  Journal Article
Gardlik, S; Rajagopalan, KV
Published in: J Biol Chem
August 5, 1990

Methods have been devised to examine the spectral properties and state of reduction of the pterin ring of molybdopterin (MPT) in milk xanthine oxidase and the Mo-containing domain of rat liver sulfite oxidase. The absorption spectrum of the native pterin was visualized by difference spectroscopy of each protein, denatured anaerobically in 6 M guanidine hydrochloride (GdnHCl), versus a sample containing the respective apoprotein and other necessary components. The state of reduction of MPT was also probed using 2,6-dichlorobenzenoneindophenol (DCIP) to measure reducing equivalents/MPT, after anaerobic denaturation of the protein in GdnHCl in the presence or absence of Hg2+. In the case of xanthine oxidase the data indicate that the terminal sulfide ligand of Mo causes the reduction of a native dihydro form of MPT to the tetrahydro level. This reduction does not occur if Hg2+ is added prior to denaturation of the protein. Based on its observed behavior, the native MPT in the Mo cofactor of xanthine oxidase is postulated to exist as a quinonoid dihydropterin. Quantitation of DCIP reduction by MPT of Mo fragment of sulfite oxidase showed a two-electron oxidation of MPT, even when the Mo fragment was denatured in the presence of Hg2+ to prevent internal reduction reactions due to sulfhydryls or sulfide. Difference spectra of DCIP-treated versus untreated Mo fragment showed that MPT had been fully oxidized. These data indicate that the native MPT in sulfite oxidase must be a dihydro isomer different from that in xanthine oxidase.

Duke Scholars

Published In

J Biol Chem

ISSN

0021-9258

Publication Date

August 5, 1990

Volume

265

Issue

22

Start / End Page

13047 / 13054

Location

United States

Related Subject Headings

  • Xanthine Oxidase
  • Spectrophotometry
  • Rats
  • Pteridines
  • Oxidoreductases Acting on Sulfur Group Donors
  • Oxidoreductases
  • Oxidation-Reduction
  • Molybdenum Cofactors
  • Molybdenum
  • Molecular Structure
 

Citation

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Gardlik, S., & Rajagopalan, K. V. (1990). The state of reduction of molybdopterin in xanthine oxidase and sulfite oxidase. J Biol Chem, 265(22), 13047–13054.
Gardlik, S., and K. V. Rajagopalan. “The state of reduction of molybdopterin in xanthine oxidase and sulfite oxidase.J Biol Chem 265, no. 22 (August 5, 1990): 13047–54.
Gardlik S, Rajagopalan KV. The state of reduction of molybdopterin in xanthine oxidase and sulfite oxidase. J Biol Chem. 1990 Aug 5;265(22):13047–54.
Gardlik, S., and K. V. Rajagopalan. “The state of reduction of molybdopterin in xanthine oxidase and sulfite oxidase.J Biol Chem, vol. 265, no. 22, Aug. 1990, pp. 13047–54.
Gardlik S, Rajagopalan KV. The state of reduction of molybdopterin in xanthine oxidase and sulfite oxidase. J Biol Chem. 1990 Aug 5;265(22):13047–13054.

Published In

J Biol Chem

ISSN

0021-9258

Publication Date

August 5, 1990

Volume

265

Issue

22

Start / End Page

13047 / 13054

Location

United States

Related Subject Headings

  • Xanthine Oxidase
  • Spectrophotometry
  • Rats
  • Pteridines
  • Oxidoreductases Acting on Sulfur Group Donors
  • Oxidoreductases
  • Oxidation-Reduction
  • Molybdenum Cofactors
  • Molybdenum
  • Molecular Structure