Peroxynitrite is a highly reactive nitrogen-containing oxidant formed when superoxide anion reacts with nitric oxide, a signaling molecule normally involved in regulating blood flow and immune function. This reaction happens extremely quickly, and because it consumes nitric oxide in the process, excessive peroxynitrite formation can disrupt normal nitric oxide signaling in addition to causing direct oxidative damage. Peroxynitrite is capable of damaging lipids, proteins, and DNA, and it has a particular tendency to modify tyrosine residues in proteins through a process called nitration, which can impair protein function. It is considered part of the broader category of reactive nitrogen species (RNS) rather than pure reactive oxygen species (ROS), though the two categories overlap and interact extensively in oxidative stress pathways. Because peroxynitrite forms from the combination of superoxide and nitric oxide, conditions that increase both of these simultaneously, such as inflammation, tend to be particularly favorable for peroxynitrite generation and its associated tissue damage.

Peroxynitrite (Wikipedia)

Peroxynitrite

Chemical structure of the peroxynitrite anion
Names
IUPAC name Oxido nitrite
Identifiers
CAS Number	19059-14-4
3D model (JSmol)	Interactive image
ChEBI	CHEBI:25941
ChemSpider	94607
Gmelin Reference	674445
KEGG	C16845
PubChem CID	104806
UNII	UR67NH4U77 Y
CompTox Dashboard (EPA)	DTXSID10172540
InChI InChI=1S/HNO3/c2-1-4-3/h3H/p-1 Key: CMFNMSMUKZHDEY-UHFFFAOYSA-M
SMILES N(=O)O[O-]
Properties
Chemical formula	NO3−
Molar mass	62.005 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Peroxynitrite (sometimes called peroxonitrite) is an ion with the formula ONOO⁻. It is a structural isomer of nitrate, NO⁻
₃. Peroxynitrite is a potent reactive nitrogen species and is highly cytotoxic.