ROS: Son of Superoxide

But the horror doesn't end there. During reperfusion, enzymes known collectively as NOS (nitric oxide synthases) generate increased amounts of nitric oxide (NO) throughout the brain. NO is a potent vasodilator--just ask any fan of Viagra--and when produced by endothelial cells during reperfusion, the effect of NO is probably salutary, by increasing blood flow.

NO produced inside neurons during reperfusion, however, is another matter. This NO can combine with superoxide to form a new species, NOOO-, or ONO2-, called peroxynitrite:

O2- + NO → ONO2-

Peroxynitrite is not your friend. This molecule is much more radical than superoxide, and it's pernicious. It wants to react with everything--proteins, lipids, nucleotides, you name it. For example, when exposed to ONO2-, proteins pick up tons of nitrotyrosine residues, where ONO2- has attacked tyrosine. Naturally, this has the potentially to really gum up the protein's function. And yours. When ONO2- is around, nobody is really safe from nitrosylation.

Peroxynitrite! O NOO! You are looking at a truly evil molecule. If we didn't have it caged in this little white box right now, it would jump right out of the screen and nitrosylate your face.