Catabolite inactivation of the maltose transporter in nitrogen-starved yeast could be due to the stimulation of general protein turnover

Abstract

Addition of glucose to Saccharomyces cerevisiae inactivates the maltose transporter. The general consensus is that this inactivation, called catabolite inactivation, is one of the control mechanisms developed by this organism to use glucose preferentially whenever it is available. Using nitrogen-starved cells (resting cells), it has been shown that glucose triggers endocytosis and degradation of the transporter in the vacuole. We now show that maltose itself triggers inactivation and degradation of its own transporter as efficiently as glucose. This fact, and the observation that glucose inactivates a variety of plasma membrane proteins including glucose transporters themselves, suggests that catabolite inactivation of the maltose transporter in nitrogen-starved cells is not a control mechanism specifically directed to ensure a preferential use of glucose. It is proposed that, in this metabolic condition, inactivation of the maltose transporter might be due to the stimulation of the general protein turnover that follows nitrogen starvation.

Catabolite inactivation of the sugar transporters in is inhibited by the presence of a nitrogen source

“…It is believed that these inactivation processes are part of the mechanisms that favour the preferential use of glucose. However, this belief contrasts with the available evidence because it assumes that : (i) the inactivation is speci¢cally produced by glucose while the results show that it is produced by all tested fermentable sugars [20,23]; (ii) the inactivation a¡ects only non-glucose sugar transporters while the results show that all tested plasma membrane proteins, i.e. the uracil [24], inositol [25], and K permeases [26,27], the H -ATPase [28], and even the glucose transporters themselves [27,29,30], are inactivated by a similar mechanism.…”

“…Inactivation of sugar transporters by glucose has been almost exclusively investigated using nitrogen-starved yeast (resting cells). Since nitrogen starvation is the most in£uencing factor among the variety of factors that stimulate protein degradation [31,32], it has been proposed that the inactivation might be mainly due not to speci¢c mechanisms controlled by glucose, but to the stimulation of the general protein turnover that follows nitrogen starvation [23]. For this hypothesis to be correct, one prediction should be satis¢ed: the presence of a nitrogen source should decrease the inactivation.…”

Starvation‐induced degradation of yeast hexose transporter Hxt7p is dependent on endocytosis, autophagy and the terminal sequences of the permease

“…raffinose, ensuring that the high‐affinity transporters are rapidly removed from the plasma membrane under conditions where low‐affinity transporters like Hxt1p are expressed. However, degradation of sugar transporters by glucose has almost exclusively been investigated using nitrogen‐starved resting yeast cells to prevent the synthesis of new proteins [4–6]. In the case of maltose permease it has recently been proposed that the glucose‐induced degradation might be mainly due to the stimulation of general protein turnover caused by the nitrogen starvation conditions and not by a specific mechanism controlled by glucose [6].…”

“…However, degradation of sugar transporters by glucose has almost exclusively been investigated using nitrogen‐starved resting yeast cells to prevent the synthesis of new proteins [4–6]. In the case of maltose permease it has recently been proposed that the glucose‐induced degradation might be mainly due to the stimulation of general protein turnover caused by the nitrogen starvation conditions and not by a specific mechanism controlled by glucose [6]. Moreover, as nitrogen starvation conditions also induce autophagy, a degradative process by which cells sequester bulk cytosol into double membrane vesicles and deliver them to the vacuole for degradation [7], we asked whether this pathway might also be involved in the degradation of hexose transporters.…”

The Kinetics of Ethanol Fermentation Based on Adsorption Processes

“…11 The stability of transport protein is easily affected by the addition of ethanol, which is a protein conformation destabilizer, through the increment of protein secondary structure, disruption of protein native structure, and inducement of amyloid formation. 12 The transport can be blocked by ethanol due to the denaturation of protein through the formation of competitive bonds between the alcohol and the non-polar residues of the protein, and results in the inhibition of glucose fermentation.…”