Regulation of xanthine oxidase by nitric oxide and peroxynitrite

Chang Il Lee, Xiaoping Liu, Jay L. Zweier

Research output: Contribution to journalArticlepeer-review

125 Scopus citations


Xanthine oxidase (XO) is a central mechanism of oxidative injury as occurs following ischemia. During the early period of reperfusion, both nitric oxide (NO·) and superoxide (O2-) generation are increased leading to the formation of peroxynitrite (ONOO-); however, questions remain regarding the presence and nature of the interactions of NO· or ONOO- with XO and the role of this process in regulating oxidant generation. Therefore, we determined the dose-dependent effects of NO· and ONOO- on the O2- generation and enzyme activity of XO, respectively, by EPR spin trapping of O2- using 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide and spectrophotometric assay. ONOO- markedly inhibited both O2- generation and XO activity in dose-dependent manner, while NO· from NO· gas in concentrations up to 200 μM had no effect. Furthermore, we observed that NO· donors such as NOR-1 also inhibited O2- generation and XO activity; however, these effects were O2--dependent and blocked by superoxide dismutase or ONOO- scavengers. Finally, we found that ONOO- totally abolished the Mo(V) EPR spectrum. These changes were irreversible, suggesting oxidative disruption of the critical molybdenum center of the catalytic site. Thus, ONOO- formed in biological systems can feedback and downregulate XO activity and O2- generation, which in turn may serve to limit further ONOO- formation.

Original languageEnglish (US)
Pages (from-to)9369-9376
Number of pages8
JournalJournal of Biological Chemistry
Issue number13
StatePublished - Mar 31 2000

ASJC Scopus subject areas

  • Biochemistry


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