The glutaredoxin/glutathione post-stress recovery system is dependent on the availability of glutathione in the cell.
Blom, Erin Shelby.
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The cellular response to oxidative stress involves three interconnected processes: reactive oxygen species detoxification, adaptation and repair. Glutathionylation is an adaptive response in which glutathione binds to labile proteins protecting them from oxidative damage but also inactivating them. While it has been established that glutaredoxins play a crucial role in deglutathionylating these proteins, the kinetic regulation of this post-stress repair process is less clear. Intriguingly, aged cells have decreased glutathione levels, although the mechanistic significance of this decrease has not been well-understood. We hypothesized that in these cells, the lower glutathione levels reduced the efficiency of the glutaredoxin/glutathione system which impaired the recovery of the cell post-stress. To test this hypothesis, we used a validated computational model of the glutaredoxin/glutathione system to determine how perturbation of the glutaredoxin system affected the availability of active glutaredoxin as well as the rate of deglutathionylation. We separated the effects of the kinetic and thermodynamic components of glutaredoxin activity and found that the overall flux was primarily controlled by the kinetic effects and that the activity of the system was largely dependent on the availability of reduced glutathione. To test whether reduced deglutathionylation activity was a characteristic of aging, aging and glutathione determination experiments were undertaken in the fission yeast, Schizosaccharomyces pombe. In contrast to our hypothesis and data from other studies, fission yeast cells aged for five days were shown to have increased glutathione concentrations, from 36.62 μM to 43.09 μM in minimal media when compared with two-day old cells, except in the presence of additional glutathione or Lbuthionine sulfoximine, a glutathione synthesis inhibitor. Further, glutathionylation levels decreased or remained unchanged in the aged cultures which we speculate was due to an adaptive response by the glutathione synthesis pathway in these cells. Future experiments will need to measure both the glutaredoxin system and the metabolic pathways that provide reductive inputs into the system in order to understand the role of the glutathionylation cycle in post-stress recovery.