Fig. 5.

Oxidation levels affect the redox status of cysteines in vivo and lead to divergent cellular responses. A, The redox continuum of oxidation in the cell ranges from reductive stress to oxidative stress with low levels of oxidation present in unstressed cells. B, C, Cysteines can be oxidized to different states depending on the oxidation level in the cell. While oxoforms essential to cell survival and proliferation (yellow) are the primary type of cysteine modification found in unstressed cells, a moderate increase in oxidation leads to an adaptive response and glutathionylation (S-GSH) of cysteines. Severe oxidative stress leads to senescence or cell death and is accompanied by overoxidized cysteine oxoforms such as sulfinic (orange) and sulfonic acid (red) which are dysfunctional. Hypoxia and reductive stress disrupts essential redox reactions (red X) and can result in cell death.