Decrease of H₂O₂ Plasma Membrane Permeability during Adaptation to H₂O₂ in Saccharomyces cerevisiae^*

Abstract

Contrary to what is widely believed, recent published results show that H₂O₂ does not freely diffuse across biomembranes. The fast removal of H₂O₂ by antioxidant enzymes is able to generate a gradient if H₂O₂ is produced in a different compartment from that containing the enzymes (Antunes, F., and Cadenas, E. (2000) FEBS Lett. 475, 121-126). In this work, we extended these studies and tested whether an active regulation of biomembranes permeability characteristics is part of the cell response to oxidative stress. Using Saccharomyces cerevisiae as a model, we showed that: (a) H₂O₂ gradients across the plasma membrane are formed upon exposure to external H₂O₂; (b) there is a correlation between the magnitude of the gradients and the resistance to H₂O₂;(c) there is not a correlation between the intracellular capacity to remove H₂O₂ and the resistance to H₂O₂; (d) the plasma membrane permeability to H₂O₂ decreases by a factor of two upon acquisition of resistance to this agent by pre-exposing cells either to nonlethal doses of H₂O₂ or to cycloheximide, an inhibitor of protein synthesis; and (e) erg3Δ and erg6Δ mutants, which have impaired ergosterol biosynthesis pathways, show higher plasma membrane permeability to H₂O₂ and are more sensitive to H₂O₂. Altogether, the regulation of the plasma membrane permeability to H₂O₂ emerged as a new mechanism by which cells respond and adapt to H₂O₂. The consequences of the results to cellular redox compartmentalization and to the origin and evolution of the eukaryotic cell are discussed.