Oxidation of tetrahydrobiopterin by peroxynitrite or oxoferryl species occurs by a radical pathway

• Published in: Free radical research Vol. 35; no. 6; p. 709
• Main Authors: Kohnen, S L, Mouithys-Mickalad, A A, Deby-Dupont, G P, Deby, C M, Lamy, M L, Noels, A F
• Format: Journal Article
• Language: English
• Published: England 01-01-2001
• Subjects: Biopterins - analogs & derivatives; Biopterins - metabolism; Chlorine - metabolism; Electron Spin Resonance Spectroscopy; Free Radicals - metabolism; Oxidation-Reduction; Oxides - metabolism; Peroxynitrous Acid - metabolism; Signal Transduction; Spectrophotometry, Ultraviolet; Time Factors
• ISSN: 1071-5762
• DOI: 10.1080/10715760100301221

The molecular mechanisms of tetrahydrobiopterin (BH4) oxidation by peroxynitrite (ONOO-) was studied using ultra-weak chemiluminescence, electron paramagnetic resonance (EPR) and UV-visible diode-array spectrophotometry, and compared to BH4 oxidation by oxoferryl species produced by the myoglobin/hydrogen peroxide (Mb/H2O2) system. The oxidation of BH4 by ONOO- produced a weak chemiluminescence, which was altered by addition of 50 mM of the spin trap alpha-(4-pyridyl-1-oxide)-N-tert butylnitrone (POBN). EPR spin trapping demonstrated that the reaction occurred at least in part by a radical pathway. A mixture of two spectra composed by an intense six-line spectrum and a fleeting weak nine-line one was observed when using ONOO-. Mb/H2O2 produced a short-living light emission that was suppressed by the addition of BH4. Simultaneous addition of POBN, BH4 and Mb/H2O2 produced the same six-line EPR spectrum, with a signal intensity depending on BH4 concentration. Spectrophotometric studies confirmed the rapid disappearance of the characteristic peak of ONOO- (302 nm) as well as substantial modifications of the initial BH4 spectrum with both oxidant systems. These data demonstrated that BH4 oxidation, either by ONOO- or by Mb/H2O2, occurred with the production of activated species and by radical pathways.