Signaling Functions of Reactive Oxygen Species

We review signaling by reactive oxygen species, which is emerging as a major physiological process. However, among the reactive oxygen species, H2O2 best fulfills the requirements of being a second messenger. Its enzymatic production and degradation, along with the requirements for the oxidation of thiols by H2O2, provide the specificity for time and place that are required in signaling. Both thermodynamic and kinetic considerations suggest that among possible oxidation states of cysteine, formation of sulfenic acid derivatives or disulfides call be relevant as thiol redox switches in signaling. In this Work, the general constraints that are required for protein thiol oxidation by H2O2 to be fast enough to be relevant for signaling are discussed ill light of the mechanism of oxidation of the catalytic cysteine or selenceysteine in thiol peroxidases. While the nonenzymatle reaction between thiol and H2O2 is, in most cases, too slow to be relevant in signaling, the enzymatic catalysis of thiol oxidation by these peroxidases provides a potential mechanism for redox signaling.