Xanthine oxidase has been recognized as an important source of oxygen free radicals in ischemia-reperfusion injury. In order to study enzyme in biological tissues, the conversion of of pterin (2-amino-4-hydroxypteridine) of isoxanthopterin provides the basis for a very sensitive fluorometric assay. Xanthine oxidase is typically assayed in the presence of pterin only, while an electron acceptor which replaces NAD+ is used to determine the combined xanthine dehydrogenase plus xanthine oxidase activity. 2,6-Dichlorophenol-indophenol has been used as an electron acceptor in this aasay. However, it was found in this study that it acts as an effective competitive inhibitor for xanthine oxidase. We conclude that methylene blue is the electron acceptor of choice in the fluorometric assays for xanthine oxidase.
Bibliographical noteFunding Information:
S. Mest was supported by the University of Washington's Medical Student Research Training Program. F.J.G.M. van Kuijk was supported by the Air Force Office of Scientific Research, Air Force Systems Command, USAF, under grant No. 90-0327. The U.S. government is authorized to reproduce and distribute reprints for governmental purposes notwithstanding any copyright notation thereon. The authors would like to thank Lynne J. Eddy, Institute of Toxicology, USC, Los Angeles, CA, for assistance with the assay.
- Competitive inhibitor
- Fluorometric assay
- Free radicals
- Xanthine dehydrogenase
- Xanthine oxidase