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Paradoxical stabilization of the neutral flavin semiquinone of xanthine dehydrogenase at high pH.
Biochem Biophys Res Commun. 1993 Aug 16; 194(3):1097-102.BB

Abstract

The pH dependence of the behavior of chicken liver xanthine dehydrogenase in the course of reductive titrations with sodium dithionite has been examined. Below pH 8.5, the behavior of xanthine dehydrogenase is similar to that of the much better understood milk xanthine oxidase, with the amount of neutral semiquinone accumulating transiently in the course of the titration increasing somewhat as the pH decreases. At pH 10, however, an anomalously large accumulation of the neutral semiquinone is observed by both UV/visible and EPR spectroscopy. Treatment of xanthine dehydrogenase with the thiol reagent iodoacetamide significantly diminishes the ability of the enzyme to stabilize the neutral flavin semiquinone at high pH. These data are consistent with the presence of a protein thiol in the immediate vicinity of the flavin, whose ionization above pH 8.5 results in thermodynamic stabilization of the neutral flavin semiquinone over the anionic form.

Authors+Show Affiliations

Department of Medical Biochemistry, Ohio State University, Columbus 43210.No affiliation info available

Pub Type(s)

Journal Article
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

8394700

Citation

Ratnam, K, and R Hille. "Paradoxical Stabilization of the Neutral Flavin Semiquinone of Xanthine Dehydrogenase at High PH." Biochemical and Biophysical Research Communications, vol. 194, no. 3, 1993, pp. 1097-102.
Ratnam K, Hille R. Paradoxical stabilization of the neutral flavin semiquinone of xanthine dehydrogenase at high pH. Biochem Biophys Res Commun. 1993;194(3):1097-102.
Ratnam, K., & Hille, R. (1993). Paradoxical stabilization of the neutral flavin semiquinone of xanthine dehydrogenase at high pH. Biochemical and Biophysical Research Communications, 194(3), 1097-102.
Ratnam K, Hille R. Paradoxical Stabilization of the Neutral Flavin Semiquinone of Xanthine Dehydrogenase at High PH. Biochem Biophys Res Commun. 1993 Aug 16;194(3):1097-102. PubMed PMID: 8394700.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Paradoxical stabilization of the neutral flavin semiquinone of xanthine dehydrogenase at high pH. AU - Ratnam,K, AU - Hille,R, PY - 1993/8/16/pubmed PY - 1993/8/16/medline PY - 1993/8/16/entrez SP - 1097 EP - 102 JF - Biochemical and biophysical research communications JO - Biochem Biophys Res Commun VL - 194 IS - 3 N2 - The pH dependence of the behavior of chicken liver xanthine dehydrogenase in the course of reductive titrations with sodium dithionite has been examined. Below pH 8.5, the behavior of xanthine dehydrogenase is similar to that of the much better understood milk xanthine oxidase, with the amount of neutral semiquinone accumulating transiently in the course of the titration increasing somewhat as the pH decreases. At pH 10, however, an anomalously large accumulation of the neutral semiquinone is observed by both UV/visible and EPR spectroscopy. Treatment of xanthine dehydrogenase with the thiol reagent iodoacetamide significantly diminishes the ability of the enzyme to stabilize the neutral flavin semiquinone at high pH. These data are consistent with the presence of a protein thiol in the immediate vicinity of the flavin, whose ionization above pH 8.5 results in thermodynamic stabilization of the neutral flavin semiquinone over the anionic form. SN - 0006-291X UR - https://www.unboundmedicine.com/medline/citation/8394700/Paradoxical_stabilization_of_the_neutral_flavin_semiquinone_of_xanthine_dehydrogenase_at_high_pH_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S0006-291X(83)71934-0 DB - PRIME DP - Unbound Medicine ER -