AFFINITY OF GLUCOSE-TRANSPORT IN SACCHAROMYCES-CEREVISIAE IS MODULATED DURING GROWTH ON GLUCOSE

By using a modified technique to measure glucose uptake in Saccharomyc es cerevisiae, potential uncertainties have been identified in previou s determinations. These previous determinations had led to the proposa l that S. celevisine contained a constitutive low-affinity glucose tra nsporter and a glucose-repressible high-affinity transporter. We show that, upon transition from glucose-repressed to -derepressed condition s, the maximum rate of glucose transport is constant and only the affi nity for glucose changes. We conclude that the transporter or group of transporters is constitutive and that regulation of glucose transport occurs via a factor that modifies the affinity of the transporters an d not via the synthesis of different kinetically independent transport ers. Such a mechanism could, for instance, be accommodated by the bind ing of kinases causing a change in affinity for glucose.