Superoxide, Peroxy Radicals and Peroxynitrite

This spontaneous dismutation reaction proceeds most rapidly at pH 4.8, the pKa for the equilibrium between Oy and the hydroperoxy species (HOj). H2O2 is a stronger oxidant than Oy and preferentially partitions into lipid and the hydrophobic cores of globular proteins and molecules where it exerts its oxidative effects [4]. Although Oy is charged, it can cross the plasma membrane via anion channels and thus exhibit increased specificity in target selection. 

However, this reaction only proceeds very slowly under physiological condi- 

The hydroxyl radical reacts with most organic molecules at rates not far from diffusion controlled consequently it has a very short half-life and is difficult to detect directly. It follows that a major determinant of the toxicity of OT and H2O2 in vivo is the availability and location of metal ions capable of catalysing OH formation. 

---