CONTRIBUTION TO THE PHYSIOLOGICAL CHARACTERIZATION OF GLYCEROL ACTIVEUPTAKE IN SACCHAROMYCES-CEREVISIAE

Evidence is presented here that in Saccharomyces cerevisiae IGC 3507, grown either on glycerol, ethanol or acetate, glycerol is transported by a high affinity uptake system of the electrogenic proton symport ty pe, with K-m of 1.7 +/- 0.7 mM, V-max 441 +/- 19 mu mol h(-1) g(-1) dr y weight and a stoichiometry of 1:1 proton per molecule of glycerol, a t 30 degrees C and pH 5.0. No competitors were found among other polyo ls and sugars. Glycerol maximum accumulation ratios followed p.m.f. wi th extracellular pH. CCCP prevented glycerol accumulation, and inhibit ed uptake. NaCl did not interfere with H+/glycerol kinetics and energe tics. This transport system was shown to be under glucose repression a nd inactivation. Glucose-grown cells presented, instead, a lower affin ity permease for glycerol, probably a facilitated diffusion. Growth on glucose in the presence of NaCl did not induce the high affinity carr ier. The stringent control of cell physiological condition over induct ion suggests for glycerol proton symport rather a physiological role c onnected with growth under gluconeogenic conditions. (C) 1997 Elsevier Science B.V.