A comprehensive mechanistic study of the molybdoflavoenzyme xanthine oxidase is proposed focusing on two central aspects of the catalytic behavior of this important enzyme, which catalyzes the final two steps in purine catabolism. In the first aspect of the proposed work, the reductive half-reaction of the catalytic cycle will be comprehensively examined with the aim of establishing the detailed chemistry that occurs in the conversion of xanthine to uric acid. The results will be interpreted in terms of a specific chemical mechanisms proposed for the reductive half-reaction. The structure of the complex of alloxanthine with xanthine oxidase will specifically be examined in this aspect of the proposed work. This complex is thought to be a particularly stable analog to a specific catalytic intermediate, and is also of clinical significance in that its great stability is the basis for the remarkable clinical efficacy of allopurinol. This well-tolerated drug is used in the treatment of hyperuricemia associated with such diverse conditions as gout and gouty arthritis, and enzyme deficiencies in hypoxanthine-guanine phosphoribosyltransferase (Lesch-Nyhan syndrome) and glucose-6-phosphatase (von Gierke's disease). In the second aspect of the proposed work, the interaction of the four oxidation-reduction centers in xanthine oxidase will be quantitatively examined in an effort to determine the rates at which reducing equivalents equilibrate in the enzyme, and the extent to which the equilibration of reducing equivalents influences catalytic turnover. The presence in xanthine oxidase of multiple sites capable of reversibly accepting reducing equivalents offers the opportunity to examine the transfer of electrons from one biological center to another while being held at a fixed distance and orientation within a more or less rigid polypeptide matrix. This has become an area of great interest in biophysics, and the careful examination of the properties of xanthine oxidase is expectd to yield significant information regarding the principles governing electron transfer in biological systems. The mode of interaction of the various centers in xanthine oxidase may also be relevant in the production of superoxide by xanthine oxidase. This too is of clinical significance given that enzyme-generated superoxide has been proposed to play a significant role in ischemia-related tissue damage (in atherosclerosis and heart attack).

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR038917-03
Application #
3158966
Study Section
Biochemistry Study Section (BIO)
Project Start
1988-04-01
Project End
1993-03-31
Budget Start
1990-04-01
Budget End
1991-03-31
Support Year
3
Fiscal Year
1990
Total Cost
Indirect Cost
Name
Ohio State University
Department
Type
Schools of Medicine
DUNS #
098987217
City
Columbus
State
OH
Country
United States
Zip Code
43210
Xia, M; Dempski, R; Hille, R (1999) The reductive half-reaction of xanthine oxidase. Reaction with aldehyde substrates and identification of the catalytically labile oxygen. J Biol Chem 274:3323-30
Michaud, A L; Herrick, J A; Duplain, J E et al. (1998) FTIR characterization of heterocycles lumazine and violapterin in solution: effects of solvent on anionic forms. Biospectroscopy 4:235-56
Conrads, T; Hemann, C; Hille, R (1998) Formation of a tyrosyl radical in xanthine oxidase. Biochemistry 37:7787-91
Kim, J H; Ryan, M G; Knaut, H et al. (1996) The reductive half-reaction of xanthine oxidase. The involvement of prototropic equilibria in the course of the catalytic sequence. J Biol Chem 271:6771-80
Sun, J; Kahlow, M A; Kaysser, T M et al. (1996) Resonance Raman spectroscopic identification of a histidine ligand of b595 and the nature of the ligation of chlorin d in the fully reduced Escherichia coli cytochrome bd oxidase. Biochemistry 35:2403-12
Brody, M S; Hille, R (1995) The reaction of chicken liver sulfite oxidase with dimethylsulfite. Biochim Biophys Acta 1253:133-5
Hille, R; Nishino, T (1995) Flavoprotein structure and mechanism. 4. Xanthine oxidase and xanthine dehydrogenase. FASEB J 9:995-1003
Hille, R (1994) The reaction mechanism of oxomolybdenum enzymes. Biochim Biophys Acta 1184:143-69
Lorigan, G A; Britt, R D; Kim, J H et al. (1994) Electron spin echo envelope modulation spectroscopy of the molybdenum center of xanthine oxidase. Biochim Biophys Acta 1185:284-94
Ratnam, K; Hille, R (1993) Paradoxical stabilization of the neutral flavin semiquinone of xanthine dehydrogenase at high pH. Biochem Biophys Res Commun 194:1097-102

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