Xanthine Oxidase (XO) 學生 : 李威聰 指導老師 : 李惠春

Introduction  Function  Structure  Property  Gout

Function  In purine degradation, it oxidizes hypoxanthine successively to xanthine and then to uric acid

Stucture  Homodimer  Each monomer has three domains  N-terminal domain (residues 1~165):  N-terminal domain (residues 1~165): two Fe/S cofactors two Fe/S cofactors  FAD-binding domain (residues  FAD-binding domain (residues 226~553) 226~553)  The third domain (residues  The third domain (residues 590~1332): one molybdenum 590~1332): one molybdenum

 Fe/S  convert XDH (xanthine dehydrogenase) to XO dehydrogenase) to XO FAD  reduction of O 2 FAD  reduction of O 2 Molybdenum  oxidative hydroxylation Molybdenum  oxidative hydroxylation of purine of purine

Property  Ubiquitous among species and within the various tissues  Normally it exists in the liver and jejunum  determination of serum xanthine  determination of serum xanthine oxidase level serves as a sensitive oxidase level serves as a sensitive indicator of acute liver damage indicator of acute liver damage

 In individuals, 90% is XDH form, and 10% is XO form 10% is XO form  XDH  XO (oxidation of sulfhydryl or  XDH  XO (oxidation of sulfhydryl or proteolysis) proteolysis)  Difference between XO & XDH: XO  XH+H 2 O+O 2  X=O+H 2 O 2 XO  XH+H 2 O+O 2  X=O+H 2 O 2 XDH  XH+H 2 O+NAD +  X=O+NADH XDH  XH+H 2 O+NAD +  X=O+NADH

 Other names: xanthine oxidoreductase, hypoxanthine oxidase, hypoxanthine- xanthine oxidase

Gout  A form of arthritis caused by excess uric acid (hyperuricemia)  Complication can result death  Cause: heredity, diet, fatness, sex, excessive exercise, drug, alcohol, and some diseases

 Drug can decrease patients’ pains and prevent it  an attack of acute gout: colchicine  an attack of acute gout: colchicine  lower conc. of uric acid: allopurinol  lower conc. of uric acid: allopurinol