THE ROLE OF AN ACTIVE-TRANSPORT MECHANISM IN GLYCEROL ACCUMULATION DURING OSMOREGULATION BY ZYGOSACCHAROMYCES-ROUXII

At water activities (aw) of 0.998 (no osmoticum) and 0.960 aw(NaCl), the affinity (Km) of glycerol transport by Zygosaccharomyces rouxii was 25.6 and 6.4 mmol/l respectively. The maximum uptake rate (Vmax) was ca. 2.3 μmol/g/min at both aw's. However, at an awof 0.960 using polyethylene glycol (PEG) 400 the Kmand Vmax for glycerol transport increased to 61.1 mmol/l and 32.2 μmol/g per minute respectively. This suggests that different glycerol transport mechanisms operate during stress by the two osmotica. The addition of uncouplers (2,4-dinitrophenol or carbonylcyanide-m-chlorophenylhydrazine) resulted in the outflow of accumulated [14C]glycerol from Z. rouxii after on osmotic upshock indicating that an active transport mechanism was operative. The transport mechanism was specific for glycerol since other polyols (mannitol, meso-erythritol and arabitol) had no effect on the uptake rate. During upshock from 0.998 to 0.960 aw(NaCl), a transient increases in the rate of [14C]glycerol uptake was observed. However, if PEG 400 was used as osmoticum, the rate of glycerol uptake failed to increase. © 1990 Springer-Verlag.