The latter modification plays a major role in regulating enzyme activities and protein structures. Sglutathionylation, formerly known as S-thiolation, is the formation of protein Desacetyl-asperulosidic-acid mixed-disulfides with glutathione. Irreversible modification occurs when protein cysteine residues are oxidized to sulfinic and cysteic acids and this modification usually leads to protein degradation. Protein S-glutathionylation serves a unique role by connecting the pools of non-protein and protein thiols in cells under oxidant stress. It is known that protein post-translational modifications play a significant role in many biochemical functions. The best example of various modifications is protein phosphorylation and dephosphorylation. Although protein S-glutathionylation is a new addition to the list of modifications, a large body of data has shown the importance of glutathionylation. Initially, many in vitro studies have shown glutathionylation is a Dehydrodiisoeugenol switch to turn on/off enzymes�� activities. Recently, glutathionylation has been proposed as a protective mechanism in vivo to prevent enzymes from irreversible damage by oxidant stress. Moreover, protein S-glutathionylation also has been shown to be involved in signal transduction and the progression of disease. A number of S-glutathionylated proteins have been identified in vivo, i.e. actin. This line of research enlarges the understanding of novel functions associated with these glutathionylated proteins. The details of the role of glutathionylation in many cellular aspects can be found in recent reviews. The amount of glutathionylation on proteins is a dynamic process under oxidative stress. The mechanism for the addition of glutathione to protein reactive cysteine residues is still somewhat ambiguous, but the mechanism of deglutathionylation is well characterized. For example, glutaredoxin, a dethiolase, is known to specifically catalyze the reversed reaction of glutathionylated proteins. In this report, our data shows specific S-glutathionylated proteins in HEK 293 cells using different oxidants.