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Fumiyuki Yamakura, Takashi Matsumoto, Keiichi Ikeda, Hikari Taka, Tsutomu Fujimura, Kimie Murayama, Eiji Watanabe, Makoto Tamaki, Takeo Imai, Kenji Takamori, Nitrated and Oxidized Products of a Single Tryptophan Residue in Human Cu,Zn-Superoxide Dismutase Treated with Either Peroxynitrite-Carbon Dioxide or Myeloperoxidase-Hydrogen Peroxide-Nitrite, The Journal of Biochemistry, Volume 138, Issue 1, Jul. 2005, Pages 57–69, https://doi.org/10.1093/jb/mvi095
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Abstract
We reported previously that a single tryptophan residue, Trp32, in human Cu,Zn-superoxide dismutase is specifically modified by peroxynitrite-CO2 [Yamakura et al. (2001) Biochim. Biophys. Acta 1548, 38–46]. In this study, we modified Cu,Zn-superoxide dismutase by using a combination of myeloperoxidase, hydrogen peroxide, and nitrite. The modified enzyme showed no loss of copper and zinc, and 15% less enzymatic activity. Trp32 was the only significant amino acid lost. After trypsin digestion of the modified SOD with peroxynitrite-CO2 and the myeloperoxidase system, six newly appearing peptides containing tryptophan derivatives were observed on microLC-ESI-Q-TOF mass analyses and HPLC with a photodiode-array detector. The derivatives of the tryptophan residue exhibiting mass increases of 4, 16 (2 peaks), 32, 45 (major), and 45 Da (minor) were identified as kynurenine, oxindole-3-alanine and its derivatives, dihydroxytryptophan, 6-nitrotryptophan and 5-nitrotryptophan, respectively. We further identified 6-nitrotryptophan from the 1H-NMR spectrum for the pronase-digested product and calculated the yield of 6-nitrotryptophan as being about 30% for each of the modification methods. The tryptophan residue in the modified human Cu,Zn-superoxide dismutase gave the same spectra for the products including 6-nitrotryptophan as the major nitrated product with the two different modification systems.