Synergistic fungicidal activity of Cu2+ and allicin, an allyl sulfur compound from garlic, and its relation to the role of alkyl hydroperoxide reductase 1 as a cell surface defense in Saccharomyces cerevisiae

Cu2+ showed a dose-dependent fungicidal activity against Saccharomyces cerevisiae cells, and its lethal effect was extremely enhanced in the presence of allicin, an allyl sulfur compound from garlic. The fungicidal activity of Cu2+ was unaffected or rather attenuated by other sulfur-containing compounds such as N-acetyl-cysteine, l-cysteine or dithiothreitol. Ca2+ could absolutely protect against the lethal effect of Cu2+ itself, but showed no protection against the fungicidal activity of Cu2+ newly generated in combination with allicin. Cu2+ accelerated an endogenous generation of reactive oxygen species (ROS) in S. cerevisiae cells at a lethal concentration, but such intracellular oxidative stress induction was not observed during cell death progression upon treatment with Cu2+ and allicin. A surfactant, sodium N-lauroyl sarcosinate (SLS), enhanced the solubilization of a few proteins including alkyl hydroperoxide reductase 1 (AHP1) in intact cells, accounting for the absence of this protein in the extract from allicin-treated cells. Allicin-treated cells were rendered extremely sensitive to the subsequent Cu2+ treatment as in the case of SLS-treated cells. Allicin-treated cells and SLS-treated cells similarly showed an increased sensitivity to exogenously added tert-butyl hydroperoxide (t-BOOH), an organic peroxide that is detoxified by the action of AHP1. Our study suggests that allicin influences the mode of cell surface localization or the related function of AHP1 as a defense against phospholipid peroxidation by the external action of Cu2+.