D-arabinose countertransport in Bakers' yeast.

The initial rate of the glucose-induced countertransport of d-arabinose was measured at several concentrations of extracellular glucose. These data permit the calculation of the intracellular concentration of free glucose, and, if the rate of glucose metabolism is known, the maximal rate of glucose transport can be estimated. Since the maximal transport rate remained essentially constant when the extracellular glucose concentration was increased from 2 to 100 mm, the results are consistent with the hypothesis that, during glucose metabolism, glucose is transported across the yeast cell membrane by a symmetrical carrier system which functions independently of metabolism.