Modulation of cellular redox equilibrium by exogenous glutathione: insights into the GSH:GSSG cycle of Saccharomyces cerevisiae under external stress conditions

ATP-dependent reduced glutathione (GSH) is significant for cellular redox control, in particular under stress. To investigate the impact of various external stress conditions on the intracellular GSH redox cycle and to analyse the effect of exogenous glutathione in mitigating these stress conditions, Saccharomyces cerevisiae (yeast) was researched for its stress tolerance by evaluating its different physiological responses. Thermal, ethanol, hydrogen peroxide (H₂O₂) and hydroxyurea (HU) stress conditions were applied independently and in various combinations to yeast cells without or with 5 mM exogenous glutathione application at different time points of 0–2 h, 3–6 h, 6–12 h, 12–24 h, and >24 h, and the GSH : GSSG ratios of different yeast cell organelles, such as mitochondria, the cytosol and the nucleus, were quantified. Our findings revealed the response of yeast cells under various external stress conditions via spot assays, identified the role of the GSH redox cycle in reducing the effects of external stress conditions that resulted in a marked depletion of the GSH pool, and found an effective dose concentration (5 mM exogenous glutathione) under external stress conditions that significantly enhanced the intracellular GSH : GSSG ratio by acting as an antioxidant, mitigating the oxidative and environmental damage and boosting the GSH redox ratio. This is the first report to assess the GSH-mediated thermal, alcohol, hydrogen peroxide (H₂O₂) and hydroxyurea (HU) stress tolerance of Saccharomyces cerevisiae. Therefore, the exogenous application of an effective concentration of glutathione to protect against various types of external stress can be an effective approach for augmenting the yeast defense system and supporting yeast survival under the adverse conditions encountered in industrial and biotechnological applications.