ABSTRACT
This chapter focuses on how myeloperoxidase unleashes the oxidation potential of hydrogen peroxide and exploits it to produce oxidants that are highly toxic to microorganisms and human cells. Myeloperoxidase functions as a classical peroxidase when compound I oxidizes substrates by removing a single electron to produce compound II and a substrate free radical. Compound II —an oxoferryl complex—reacts with a second substrate molecule to produce another radical and regenerate the ferric enzyme. Compound III can be represented as the electronically equivalent structures of superoxide bound to ferric iron or molecular oxygen bound to ferrous iron. Its main physiological substrate appears to be superoxide which reduces it in a favorable reaction to either compound I or ferric enzyme plus hydrogen peroxide. The skepticism leveled at true catalase activity for hydrogen peroxide breakdown is understandable because the mechanism fails to take into account the relative difficulty of forming compound I.
