Electron paramagnetic resonance properties and oxidation-reduction potentials of the molybdenum,flavin, and iron-sulfur centers of chicken liver xanthine dehydrogenase |
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Authors: | Michael J Barber Michael P Coughlan Masayuki Kanda KV Rajagopalan |
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Institution: | Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710 U.S.A. |
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Abstract: | The oxidation-reduction potentials of the various prosthetic groups in the native and desulfo forms of chicken liver xanthine dehydrogenase, determined by potentiometric titration in 0.05 m potassium phosphate buffer, pH 7.8, are: Mo(VI)/Mo(V) (native), ?357 mV; Mo(VI)/Mo(V) (desulfo), ?397 mV; Mo(V)/Mo(IV) (native), ?337 mV; Mo(V)/Mo(IV) (desulfo), ?433 mV; FAD/FADH · ?345 mV; FADH · FADH2, ? 377 mV; (Fe/S)Iox/(Fe/S)Ired, ?280 mV; (Fe/S)IIox/(Fe/S)IIred, ? 275 mV. Titration at pH 6.8 revealed that the Mo and FAD centers but not the Fe/S centers are in prototropic equilibrium. Spectroscopic studies on the native and deflavinated enzymes show that environment of the flavin in xanthine dehydrogenase differs from that in bovine milk xanthine oxidase. |
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