INHIBITION OF TRANSPORT-SYSTEMS IN YEAST BY PHOTODYNAMIC TREATMENT WITH TOLUIDINE BLUE

Photodynamic treatment of yeast with the sensitizer Toluidine blue res ults in loss of cell viability. In previous investigations it was sugg ested that plasma membrane damage might be responsible for the loss of colony forming capacity. In this context the influence of photodynami c treatment on transmembrane transport systems was studied. It appeare d that the uptake of the sugars glucose, lactose and galactose, the am ino acids arginine, phenylalanine, glycine and aspartic acid and of th e inorganic compound phosphate was inhibited by photodynamic treatment . The different elements of the energy providing system necessary for active transport, viz. the plasma membrane ATPase and the protonmotive force, were not significantly affected by Toluidine blue and light, i ndicating that inhibition of transport is not caused by a reduction of the membrane potential or the transmembrane pH gradient. These observ ations suggest that the transport carriers themselves were damaged by treatment with Toluidine blue and light. This could be confirmed in ex periments, in which the lactose and galactose transport proteins of tr eated and untreated cells were reconstituted in plasma membrane vesicl es. It appeared that the carriers, obtained from photodynamically trea ted Kluyveromyces marxianus cells, had lost their transport capacity.