Turnover of the K⁺ transport system in Saccharomyces cerevisiae

Abstract

The stability of the K' transport system in Sacchurornyces cerevisiae has been studied upon inhibition of protein synthesis with cycloheximide. Addition of the antibiotic gave rise lo an inactivation of this transport. This activation followed first-order kinetics and was stimulated by the presence of a fermentable substrate. A half-life of about 4 h could be calculated in the presence of glucose. The results indicate that, similarly to sugar carriers, K' transport system is less stable than the bulk of proteins of this organism.

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

“…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.…”

Elimination of Defective α-Factor Pheromone Receptors

“…There are numerous examples of yeast plasma membrane proteins that are removed and degraded in response to regulatory cues-i.e., ligand-mediated endocytosis (17,58), nutrient deprivation (15,20,42,47), and control of ion homeostasis (49). Other plasma membrane proteins are subject to high constitutive rates of degradation (5,7,18,39). We report the first example in which a plasma membrane protein is eliminated from the cell surface because of a structural defect.…”

Involvement of endocytosis in catabolite inactivation of the K+ and glucose transport systems in Saccharomyces cerevisiae

“…35°C produced a decrease of about 20% in the ATPase activity of the mutants as compared with the wild-type and the transformed cells ( Table 2) and it has been shown that this low decrease has no significant effect on the K ÷ transport activity [2,15].…”

“…Inactivation of the K ÷ and glucose transports were triggered by suspending the cells in a minimal medium as described [9] in the presence of 2% glucose, 10 /zg m1-1 cycloheximide, and the appropriate nutrients. After incubation at 24°C or 35°C for the indicated periods in a rotatory shaker (200 rpm), K ÷ transport activity was measured as described [2]. For this purpose the cells were depleted beforehand of intracellular K ÷ by incubation in the presence of NaN 3 as described earlier [10].…”

“…Most proteins in Saccharomyces cerevisiae are stable for long periods of time under different metabolic conditions [1]. Several plasma membrane proteins behave differently in this respect, in that a rapid and irreversible inactivation is observed upon arrest of protein synthesis [2][3][4]. This inactivation, that is known in the literature as catabolite inactivation [5], is dependent on energy, stimulated by fermentable substrates [2][3][4] and due to proteolysis [6].…”