Researchers found that schwannoma cells produce an oxidant and nitrating agent, peroxynitrite
, which modifies an amino acid, tyrosine, in proteins.
Nitrotyrosine is formed by the interaction of peroxynitrite
with the tyrosine residues of proteins, and it can be used to evaluate the potential cytotoxic effects of nitric oxide.
The toxic one is peroxynitrite
that inflicts blood vessel damage.
[H.sub.2]S may easily react with certain compounds, especially with reactive oxygen and nitrogen species, such as superoxide radical anion ([O.sub.2-]), [H.sub.2][O.sub.2], peroxynitrite
(ONOO-), and hypochlorite (CIO-) (22-24).
It is known that FORs react with NO and cause formation of peroxynitrite
and this cytotoxic oxidant disrupts the function of cellular proteins via the nitration of proteins and leads to endothelial dysfunction.
Furthermore, NO easily reacts with superoxide, forming peroxynitrite
, and reduces NO bioavailability [28, 29].
The over-produced iNOS-dependent formation of NO may cause serious lung damage though the formation of peroxynitrite
(reactive nitrogen species - RNS) combining with superoxide [36, 39, 40].
For instance, hydroxyl radicals and peroxynitrite
bursts generated in some acute disease and more in degenerative disease create more and larger PPPs.
This eliminates the possibility of interaction between NO and superoxide with the formation of toxic peroxynitrite
Superoxide radicals augment apoptosis, cause formation of peroxynitrite
and can lead to dysfunction of the endothelium (5,8,9).
[17, 18] have showed that the contractile carotid hyperreactivity underlying cerebrovascular complication in stressed diabetic animals involves the upregulation of NADPH/Nox4 oxidase-driven generation of hydrogen peroxide ([H.sub.2][O.sub.2])  and inducible nitric oxide synthase (iNOS)-driven generation of peroxynitrite
. The product of the superoxide anion and NO chemical reaction is another factor that inhibits effector T cells .