Sodium peroxynitrite

All chemicals and reagents were purchased from Sigma-Aldrich (St. Louis, MO) in the best available grade, unless otherwise noted. Rat brains, stripped of the meninges, were obtained from Pel-Freez Biologicals (Rogers, AR). Sodium peroxynitrite (100–200 mM in 4.7% sodium hydroxide) was obtained from EMD Millipore (Billerica, MA) and was aliquoted and stored at −80°C for up to 6 months and then thawed immediately before use. Sulfo-NHS-SS-Biotin and Aminolink aldehyde-agarose beads were purchased from Thermo Fisher Scientific (Waltham, MA), and Strata-X C18 columns were purchased from Phenomenex (Torrance, CA). The histone H1.2-derived peptide, ALAAAG(Y-NO₂)DVEK, was custom-synthesized by Genscript (Piscataway, NJ).

Pure water was taken from a Barnstead™ GenPure™ xCAD plus water purification system (Thermo Scientific, Braunschweig, Germany). The water was autoclaved at 121 ${}^{\circ }$ C for 20 min and filtered three times through a sterile 0.1 µm pore diameter polyethersulfone (PES) vacuum filter unit (VWR International, Radnor, PA, USA). Recombinant timothy grass (Phleum pratense) pollen allergen 5 (Phl p 5.0101) was obtained from Biomay AG (Vienna, Austria), and a stock solution (1 mg mL⁻¹) was prepared with pure water prior to each experiment. The solution was reconstituted at room temperature for at least 30 min to ensure complete reconstitution of the protein. Sodium peroxynitrite (160–200 mM) was purchased from Merck (Darmstadt, Germany), and ammonium bicarbonate (NH₄HCO₃), acetonitrile (ACN), Tris-HCl, Glycerol, SDS, and monobasic sodium phosphate monohydrate (NaH₂PO₄· H₂O) were from Carl Roth GmbH & Co. KG (Karlsruhe, Germany). A 150 mM NaH₂PO₄· H₂O buffer was prepared, and the pH was adjusted to 7 by the addition of sodium hydroxide (NaOH). NaOH and water with 0.1% trifluoroacetic acid (TFA) were obtained from VWR International GmbH (Darmstadt, Germany). $\mathsf{\alpha }$ -Cyano-4-hydroxycinnamic acid (HCCA, ultrapure, J67635) was purchased from Th. Geyer GmbH & Co. KG (Renningen, Germany). Trifluoroacetic acid (TFA, LC-MS grade, 85183) was obtained from Thermo Fisher Scientific (Braunschweig, Germany).