Asymmetry of glucose transport in the yeast, Kluyveromyces lactis.

Uptake and efflux of 6-deoxy-D-[3H]glucose and of 2-deoxy-D-[14C]glucose by the yeast Kluyveromyces lactis was studied. The tritiated, nonphosphorylatable hexose analogue leaves the cell in the absence and presence of intracellular 2-deoxy-D-glucose 6-phosphate. In energy-rich cells containing pools of hexose 6-phosphate, 2-deoxy-D-glucose is trapped in the cells, for it neither effluxes into glucose-free medium nor exchanges with external, free sugar. In starved, poisoned cells containing negligible amounts of 2-deoxy-D-glucose 6-phosphate, 2-deoxy-D-glucose does leave the cells upon transfer to glucose-free medium. An involvement of analogue structure and availability of metabolites of energy-rich cells in hexose retention is suggested. An internal pool of 6-deoxy-D-glucose does not affect the rate of uptake of 6-deoxy-D-[3H]glucose, nor does internal 2-deoxy-D-[14C]glucose 6-phosphate influence that rate. Hence, transport of glucose by this yeast is probably not regulated by internal pools of glucose 6-phosphate.