A Yeast Cell Sugar Compartment. II: Sorbose Efflux.

Usual type efflux curves, showing two or more rates, were obtained with yeast cells preloaded from sorbose solutions of widely different concentrations. Extrapolations of the slow rate portions of such curves from cells preloaded for successively longer periods of time provided a measure of sorbose influx into an intracell compartment an influx which occurred at a slower rate than total cell influx. Efflux from the compartment was speeded by fermentable sugars the usual rate was resumed when the sugar was removed the effect was blocked by iodoacetic acid, but not by cycloheximide. Other sugars which compete with sorbose for transport across the external cell membrane did not compete for transport across the compartment membrane low temperatures reduced sorbose passage across the external membrane much more than across the compartment membrane. Fermentable sugars evidently increased the permeability of the compartment membrane, which decreased again when the sugar was removed or its metabolism blocked the lack of competition with other sugars and the effects of low temperatures on sorbose loss indicate that a facilitated transport system does not function. Modified author abstract