KINETICS AND ENERGETICS OF TREHALOSE TRANSPORT IN SACCHAROMYCES-CEREVISIAE

Cells of Saccharomyces cerevisiae are able to transport trehalose agai nst a concentration gradient, without efflux or counterflow of the lab eled substrate. Uptake was inhibited by uncouplers, acetic acid, and o rganic mercury compounds. The addition of trehalose resulted in alkali nization of the medium. The ratio of H+ depletion to trehalose uptake by yeast cells was approximately 1:1, which indicates the existence of a trehalose-H+ symporter in these cells. The optimum pH for this acti ve H+-trehalose symport was 5.0, and both the K-m and the V-max were n egatively affected by increasing or decreasing the extracellular pH fr om its optimum value. Kinetic studies showed the existence of at least two different trehalose transport activities in yeast cells: a high-a ffinity H+-trehalose symporter (K-m = 4 mM), and a low-affinity transp ort activity (K-m > 100 mM) that could be a facilitated diffusion proc ess. The high-affinity H+-trehalose symporter was repressed by glucose , whereas the low-affinity uptake was constitutively expressed in S. c erevisiae.