FIG. 5.

Two alternative models for the actions of H₂O₂ as a secondary messenger. The conventional model (top) involves direct actions of H₂O₂ on adjacent Cys residues within a signaling molecule to form a disulfide bond that alters conformation of the active site and the activation state. A new model (bottom) has been proposed in which peroxidases such as GPx1 promote the oxidation of adjacent Cys residues and formation of disulfide bonds. In this sense, the actions of H₂O₂ are indirect and the direct affects are determined by levels and locations of GPX1 and GSH. Cys, cysteine; GSH, glutathione; GPX, glutathione peroxidase.