Summary: Compounds (e.g. -isohumulone) derived from flowers of the hop plant ( L.) protect beer from spoilage. Cells of IFO 3960 did not die when they were exposed to 40 μM--isohumulone for up to 120 h. At higher concentrations (80, 120 μM) death occurred after a lag period of about 30 h. -Isohumulone dissipated the transmembrane pH gradient of non-growing cells and reduced their ability to accumulate L-[U-C]leucine. The membrane potential was dissipated to a smaller extent. Addition of -isohumulone to cells that had accumulated L[U-C]leucine, under conditions in which no synthesis of protein took place, caused slow leakage of radiolabelled leucine. -Isohumulone did not inhibit the activity of the proton-translocating membrane ATPase. Potentiometric experiments with resting cell suspensions suggested that -isohumulone acted as an ionophore of the mobile-carrier type, causing electroneutral exchange of H for divalent cations such as Mn. A second monovalent cation (e.g. K) was essential for protonophoric activity.


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