Peroxynitrite-induced nitration of tyrosine hydroxylase. Identification of tyrosines 423, 428, and 432 as sites of modification by matrix-assisted laser desorption ionization time-of-flight mass spectrometry and tyrosine-scanning mutagenesis

Donald M. Kuhn, Mahdieh Sadidi, Xiuli Liu, Christian Kreipke, Timothy Geddes, Chad Borges, J. Throck Watson

Research output: Contribution to journalArticle

45 Scopus citations

Abstract

Tyrosine hydroxylase (TH), the initial and rate-limiting enzyme in the biosynthesis of the neurotransmitter dopamine, is inactivated by peroxynitrite. The sites of peroxynitrite-induced tyrosine nitration in TH have been identified by matrix-assisted laser desorption time-of-flight mass spectrometry and tyrosine-scanning mutagenesis. V8 proteolytic fragments of nitrated TH were analyzed by matrix-assisted laser desorption time-of-flight mass spectrometry. A peptide of 3135.4 daltons, corresponding to residues V410-E436 of TH, showed peroxynitrite-induced mass shifts of +45, +90, and +135 daltons, reflecting nitration of one, two, or three tyrosines, respectively. These modifications were not evident in untreated TH. The tyrosine residues (positions 423, 428, and 432) within this peptide were mutated to phenylalanine to confirm the site(s) of nitration and assess the effects of mutation on TH activity. Single mutants expressed wild-type levels of TH catalytic activity and were inactivated by peroxynitrite while showing reduced (30-60%) levels of nitration. The double mutants Y423F,Y428F, Y423F,Y432F, and Y428F,Y432F showed trace amounts of tyrosine nitration (7-30% of control) after exposure to peroxynitrite, and the triple mutant Y423F,Y428F,Y432F was not a substrate for nitration, yet peroxynitrite significantly reduced the activity of each. When all tyrosine mutants were probed with PEO-maleimide activated biotin, a thiol-reactive reagent that specifically labels reduced cysteine residues in proteins, it was evident that peroxynitrite resulted in cysteine oxidation. These studies identify residues Tyr423, Tyr428, and Tyr432 as the sites of peroxynitrite-induced nitration in TH. No single tyrosine residue appears to be critical for TH catalytic function, and tyrosine nitration is neither necessary nor sufficient for peroxynitrite-induced inactivation. The loss of TH catalytic activity caused by peroxynitrite is associated instead with oxidation of cysteine residues.

Original languageEnglish (US)
Pages (from-to)14336-14342
Number of pages7
JournalJournal of Biological Chemistry
Volume277
Issue number16
DOIs
StatePublished - Apr 19 2002
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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