Hydrogen peroxide is the major oxidant product of xanthine oxidase.
Xanthine oxidase (XO) is a critical source of reactive oxygen species (ROS) in inflammatory disease. Focus, however, has centered almost exclusively on XO-derived superoxide (O(2)(*-)), whereas direct H(2)O(2) production from XO has been less well investigated. Therefore, we examined the relative quantities of O(2)(*-) and H(2)O(2) produced by XO under a range (1-21%) of O(2) tensions. At O(2) concentrations between 10 and 21%, H(2)O(2) accounted for approximately 75% of ROS production. As O(2) concentrations were lowered, there was a concentration-dependent increase in H(2)O(2) formation, accounting for 90% of ROS production at 1% O(2). Alterations in pH between 5.5 and 7.4 did not affect the relative proportions of H(2)O(2) and O(2)(*-) formation. Immobilization of XO, by binding to heparin-Sepharose, further enhanced relative H(2)O(2) production by approximately 30%, under both normoxic and hypoxic conditions. Furthermore, XO bound to glycosaminoglycans on the apical surface of bovine aortic endothelial cells demonstrated a similar ROS production profile. These data establish H(2)O(2) as the dominant (70-95%) reactive product produced by XO under clinically relevant conditions and emphasize the importance of H(2)O(2) as a critical factor when examining the contributory roles of XO-catalyzed ROS in inflammatory processes as well as cellular signaling.
Kelley
Eric E
EE
Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA. ekelley@pitt.edu
Khoo
Nicholas K H
NK
Hundley
Nicholas J
NJ
Malik
Umair Z
UZ
Freeman
Bruce A
BA
Tarpey
Margaret M
MM
D000818:Animals; D002021:Buffers; D002417:Cattle; D002470:Cell Survival; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000201:enzymology; D006861:Hydrogen Peroxide / Q000737:chemistry / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D008954:Models, Biological; D016877:Oxidants / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D010101:Oxygen Consumption; D015398:Signal Transduction; D014969:Xanthine Oxidase / Q000737:chemistry / Q000378:metabolism*
D002021:Buffers; D016877:Oxidants; D006861:Hydrogen Peroxide; D014969:Xanthine Oxidase; D010100:Oxygen