Summary: The sugar transport systems of are irreversibly inactivated when protein synthesis is inhibited. This inactivation is responsible for the drastic decrease in fermentation observed in ammonium-starved yeast and is related to the occurrence of the Pasteur effect in these cells. Our study of the inactivation of the glucose transport system indicates that both the high-affinity and the low-affinity components of this system are inactivated. Inactivation of the high-affinity component evidently requires the utilization of a fermentable substrate by the cells, since (i) inactivation did not occur during carbon starvation, (ii) when a fermentable sugar was added to starved cells, inactivation began, (iii) when the fermentation inhibitors iodoacetate or arsenate were added in addition to sugars, the inactivation was prevented, (iv) when a non-fermentable substrate was added instead of sugars, inactivation was also prevented. The inactivation of the low-affinity component appeared to show similar requirements. It is concluded that the glucose transport system in is regulated by a catabolite-inactivation process.


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