Nitric oxide reversibly suppresses xanthine oxidase activity

Free Radic Res. 1994 Sep;21(4):203-12. doi: 10.3109/10715769409056572.


The effects of nitric oxide (NO) on xanthine oxidase (XOD) activity and the site(s) of the redox center(s) affected were investigated. XOD activity was determined by superoxide (O2-) generation and uric acid formation. NO reversibly and dose-dependently suppressed XOD activity in both determination methods. The suppression interval also disclosed a dose-dependent prolongation. The suppression occurred irrespective of the presence or absence of xanthine; indicating that the reaction product of NO and O2-, peroxynitrite, is not responsible for the suppression. Application of synthesized peroxynitrite did not affect XOD activity up to 2 microM. Methylene blue, which is an electron acceptor from Fe/S center, prevented the NO-induced inactivation. The results indicate that NO suppresses XOD activity through reversible alteration of the flavin prosthetic site.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Enzyme Activation / drug effects
  • Nitric Oxide / pharmacology*
  • Oxidation-Reduction
  • Spectrophotometry, Atomic
  • Xanthine Oxidase / antagonists & inhibitors*
  • Xanthine Oxidase / chemistry


  • Nitric Oxide
  • Xanthine Oxidase