Strategies to determine the extent of control exerted by glucose transporton glycolytic flux in the yeast Saccharomyces bayanus

The extent to which the transport of glucose across the plasma membrane of the yeast Saccharomyces bayanus controls the glycolytic flux was determined . The magnitude of control was quantified by measuring the effect of small changes in the activity of the glucose transport system on the rate of gluc ose consumption. Two effecters were used to modulate the activity of glucos e transport: (i) maltose, a competitive inhibitor of the glucose transport system in S. bayanus (as well as in Saccharomyces cerevisiae) and (ii) extr acellular glucose, the substrate of the glucose transport system. Two appro aches were followed to derive from the experimental data the flux control c oefficient of glucose transport on the glycolytic flux: (i) direct comparis on of the steady-state glycolytic flux with the zero trans-influx of glucos e and (ii) comparison of the change in glycolytic flux with the concomitant change in calculated glucose transport activity on variation of the extrac ellular glucose concentration. Both these approaches demonstrated that in c ells of S. bayanus grown on glucose and harvested at the point of glucose e xhaustion, a high proportion of the control of the glycolytic flux resides in the transport of glucose across the plasma membrane.