The Oxygen Paradox: Biochemistry of Active Oxygen

Abstract

A book originating from an annual meeting of the Oxygen Society (Charleston, South Carolina 1995) (Davies and Ursini 1995) and dedicated to Paul Hochstein on the occasion of his retirement is entitled The Oxygen Paradox. The preface and some interesting articles define the oxygen paradox as the dual effects of oxygen, in a manner reminiscent of Fridovich’s article 20 years before in The American Scientist (Fridovich 1975). It is clear that in both instances an equilibrium is referred to and that this equilibrium is encompassed on the one hand, by the production of oxygen-centered radicals (a concept today extended to sulfur-, nitrogen-, and carbon-centered radicals) and the availability of reactants leading to their nonenzymatic decomposition (e.g., transition metals), and on the other hand, by the effective removal of these species by disproportionation to less reactive (non-radical) species or by interception by small antioxidant molecules or by specific antioxidant enzymes.

Here we survey the sources and removal of hydrogen peroxide (H₂O₂), a central molecule, the metabolism of which gains significance in light of its quantification by direct measurement or steady-state approximation. Emphasis is placed on the one- and two-electron reductions of H₂O₂, the former involving the generation of the hydroxyl radical (•OH) and the latter encompassing its reduction to H₂O upon interaction with hemoproteins yielding a hypervalent reactive state of the heme.

SOURCES OF H ₂ O₂
The cellular sources of H₂O₂ are many, and this species stems from nonenzymatic or enzymatic reactions. The former are usually encompassed by the spontaneous or superoxide-dismutase...