Reversible permeability changes in the membrane of a yeast cell sugar compartment.
Sorbose uptake by Saccharomyces cerevisiae was increased 40 to 60% by glucose and other metabolizable sugars. Neither growth nor binding accounted for the increased uptake. However, accessibility of a restrictive intracellular compartment was increased as shown by counterflow and efflux measurements. Efflux from the compartment was more than doubled by glucose. This effect was reversed by washing and was prevented by iodoacetic acid and other inhibitors, but not by cycloheximide. No evidence was found for a facilitated transport system in the compartment membrane such as exists in the external cell membrane. It was concluded that sorbose crosses the compartment membrane by simple diffusion and that a reaction requiring the metabolism of sugars increases the permeability of the membrane. Arabinose and fucose entered and were lost from the compartment like sorbose, whereas dimethylsulfoxide was unaffected by the compartment. All three of these later compounds were bound by the cells when glucose was available in uptake suspensions. Binding was prevented by iodoacetic acid, but not by cycloheximide.