Open AccessEffects of singlet oxygen on membrane sterols in the yeast Saccharomyces cerevisiae
Author(s) -
Böcking Till,
Barrow Kevin D.,
Netting Andrew G.,
Chilcott Terry C.,
Coster Hans G. L.,
Höfer Milan
Publication year - 2000
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1327.2000.01179.x
Subject(s) - ergosterol , singlet oxygen , chemistry , yeast , membrane , saccharomyces cerevisiae , biochemistry , sterol , photosensitizer , oxygen , photochemistry , organic chemistry , cholesterol
Photodynamic treatment of the yeast Saccharomyces cerevisiae with the singlet oxygen sensitizer toluidine blue and visible light leads to rapid oxidation of ergosterol and accumulation of oxidized ergosterol derivatives in the plasma membrane. The predominant oxidation product accumulated was identified as 5α,6α‐epoxy‐(22 E )‐ergosta‐8,22‐dien‐3β,7α‐diol (8‐DED). 9(11)‐dehydroergosterol (DHE) was identified as a minor oxidation product. In heat inactivated cells ergosterol is photooxidized to ergosterol epidioxide (EEP) and DHE. Disrupted cell preparations of S. cerevisiae convert EEP to 8‐DED, and this activity is abolished in a boiled control indicating the presence of a membrane associated enzyme with an EEP isomerase activity. Yeast selectively mobilizes ergosterol from the intracellular sterol ester pool to replenish the level of free ergosterol in the plasma membrane during singlet oxygen oxidation. The following reaction pathway is proposed: singlet oxygen‐mediated oxidation of ergosterol leads to mainly the formation of EEP, which is enzymatically rearranged to 8‐DED. Ergosterol 7‐hydroperoxide, a known minor product of the reaction of singlet oxygen with ergosterol, is formed at a much lower rate and decomposes to give DHE. Changes of physical properties of the plasma membrane are induced by depletion of ergosterol and accumulation of polar derivatives. Subsequent permeation of photosensitizer through the plasma membrane into the cell leads to events including impairment of mitochondrial function and cell inactivation.