Cited by 96Metal-Catalyzed Oxygenation MechanismsRedox biology and oxidative stressEnzyme Structure and Function

The Reaction of Reduced Xanthine Dehydrogenase with Molecular Oxygen

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Harris, Christopher M., Massey, Vincent·1997·Journal of Biological Chemistry

Abstract

Xanthine dehydrogenase (XDH) from bovine milk contains significant activity in xanthine/oxygen turnover assays. The oxidative half-reaction of XDH with molecular oxygen has been studied in detail, at 25 degrees C, pH 7.5, to determine the basis of the preference of XDH for NAD over oxygen as oxidizing substrate. Spectral changes of XDH accompanying oxidation were followed by stopped-flow spectrophotometry. The amount of superoxide radicals formed during oxidation was investigated to assess the ability of XDH to catalyze production of oxygen radicals. Reduced XDH reacts with oxygen in at least 4 bi-molecular steps, with 1.7-1.9 mol of superoxide per mol of XDH formed from the last 2 electrons oxidized. A model is discussed in which the flavin hydroquinone transfers electrons to oxygen to produce hydrogen peroxide at a rate constant of at least 72,000 M-1 s-1, whereas flavin semiquinone reduces oxygen to form superoxide as slow as 16 M-1 s-1. Steady-state kinetics of xanthine/oxygen and NADH/oxygen turnover of XDH were determined to have kcat values of 2.1 +/- 0.1 and 2.5 +/- 0.9 s-1, respectively, at 25 degrees C, pH 7.5. XDH is therefore capable of catalyzing the formation of reduced oxygen species at one-third the rate of xanthine/NAD turnover, 6.3 s-1 (Hunt, J., and Massey, V. (1992) J. Biol. Chem. 267, 21479-21485), in the absence of NAD. As XDH contains a significant and intrinsic xanthine oxidase activity, estimates of relative amounts of XO and XDH based solely upon turnover assays must be made with caution. Initial-rate assays containing varying amounts of xanthine, NAD, and oxygen indicate that at 100% oxygen saturation, NADH formation is only inhibited at concentrations of xanthine and NAD below Km for each substrate.

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  • This XDH ROS production only produces significant levels of ROS if NAD+ levels are low, which can happen in vascular hypoxia.

    “This reaction only produces significant levels of ROS if NAD+ levels are low; however, these conditions can happen in the setting of vascular hypoxia (406, 562).”
  • Xanthine oxidase generates H2O2 as a byproduct during oxidation of hypoxanthine and xanthine to uric acid.

    “It catalyzes the oxidation of the bases hypoxanthine and xanthine to uric acid, which is the end product of purine catabolism. H2O2 is generated as a byproduct during two oxidation steps of the enzymatic reaction, marking XO as a potential ROS source.”

    From Functions of ROS in Macrophages and Antimicrobial Immunity (2021) · cites this paper as [138]

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Research works printed but not linked: 2

  1. Segel, I. H. (1976) Biochemical Calculations, 2nd Ed., pp. 414 -415, Wiley, Inc., New York
  2. Mayhew, S. G., and Ludwig, M. L. (1975) in The Enzymes (Boyer, P. D., ed) 3rd Ed., Vol. XII, Part B, pp. 57-118, Academic Press, New York

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Authors
Harris, C. M., & Massey, V.
Affiliations
University of Michigan (US)
Corresponding author
Massey, Vincent
Venue
Journal of Biological Chemistry
Publisher
Elsevier BV
Published
1997-03
Volume
272
Issue
13
Pages
8370-8379
ISSN
0021-9258 (ISSN-L)
OpenAlex
W1966948694
Cited by
96
References
28
Citations by year
2026: 2 · 2025: 2 · 2024: 3 · 2023: 6 · 2021: 3 · 2020: 3 · 2019: 3 · 2018: 4 · 2017: 3 · 2016: 2 · 2015: 6 · 2014: 6 · 2013: 2 · 2012: 3
FWCI
3.70
Type
journal article
Language
en
Open access
Locations
  • Journal of Biological Chemistry (publishedVersion, cc-by)
  • PubMed (publishedVersion)
Funders
  • National Science Foundation (8500291)
  • National Institutes of Health
  • National Institute of General Medical Sciences (GM08270, T32GM008270)
Topics
  • Physical Sciences › Chemistry › Inorganic Chemistry › Metal-Catalyzed Oxygenation Mechanisms
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Redox biology and oxidative stress
  • Physical Sciences › Materials Science › Materials Chemistry › Enzyme Structure and Function
Keywords
xanthine dehydrogenase, reduced enzyme, molecular oxygen, superoxide, flavin semiquinone, hydrogen peroxide production, NADH oxidation, xanthine oxidation, xanthine oxidase, enzyme kinetics
MeSH terms
Animals, Cattle, Kinetics, Models, Chemical, Multienzyme Complexes, NADH, NADPH Oxidoreductases, Oxidation-Reduction, Oxygen, Superoxides, Xanthine Dehydrogenase

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