Transport of organic acid anions and guanosine into vacuoles of Saccharomyces pastorianus

Abstract

Isolated vacuoles of the yeast Saccharomyces pastorianus accumulate citrate, α‐ketoglutarate, malate and guanosine. This accumulation is Mg ATP‐dependent and inhibited by protonophores. The ionophores monensin and A23187 (electroneutral Men+/nH+‐exchange) inhibit guanosine accumulation but fail to block citrate uptake. Mg2+ ions (2 mM) increase the values of both Δ\documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \mu $\end{document}H+ components and stimulate the uptake of all the above compounds. Ca2+ ions (1 mM), hyperpolarizing the yeast vacuolar membrane and dissipating the pH gradient, inhibit guanosine uptake and stimulate that of citrate. It is concluded that guanosine is transported into yeast vacuoles by an H+/guanosine antiporter while citrate, malate and α‐ketoglutarate are translocated by a uniporter(s) at the expense of the membrane potential (positive inside).

Change in transport activities of vacuoles of the yeast Yarrowia lipolytica during its growth on glucose

“…Table 1 shows that the activity of vacuolar ATPase decreases under these growth conditions; simultaneously, the ability to form ApH' goes down (see also Figure 2). However, even at the stationary growth phase, the ATPase activity and the value of the membrane potential are close to the respective values observed in vacuoles from S. pastorianus at the stage of their active growth, and sufficient to provide citrate transport into vacuoles (Kulakovskaya et al, 1991). Ca2+-transporting activity of vacuoles also decreases during growth (Table I).…”

“…We report here that the isolated vacuoles of Y. lipolytica show the activities of H+-translocating ATPase, Ca2+-antiporter and citrate uniporter, which are close to the activities of those transporters of S . pastorianus vacuoles isolated in the middle of the logarithmic growth phase (Kulakovskaya et al, 1991). In other words, both the degree of tonoplast energization by its H+-ATPase and the presence of the citrate uniporter in the beginning of Y. lipolytica growth could support the hypothetical involvement of these organelles in citrate secretion to the medium via the putative transport vesicles by exocytosis.…”

“…lipolytica vacuoles was completely inhibited by protonophore carbonyl cyanide p-(tri-fluoromethoxy)phenylhydrazone (5 C(M) and by penetrating anion SCN-(10 mM), which dissipated the membrane potential. Therefore, we consider this transport to be dependent on the membrane potential, just as in vacuoles of S. pastorianus (Kulakovskaya et al, 1991). In contrast with S. pastorianus, Y. lipolytica vacuoles did not transport a-ketoglutarate and malate in any of the growth points studied, while the level of citrate transport in Y. lipolytica vacuoles isolated from the cells taken during active growth was close to that in S. pastorianus.…”

“…ApH and membrane potential pH gradient (ApH) and membrane potential (Em) were determined by fluorescence quenching of 9-amino-6-chloro-2-methoxyacridine and oxonol V, respectively, as described (Kulakovskaya et al, 1991), using a Hitachi-850 microfluorimeter (Japan). sorbitol, 10 m~-N-morpholino-2-ethanesulfonic acid (Mes)-Tris, pH 7.2) containing 8% Ficoll, and 0.2% bovine serum albumin (BSA), free from fatty acids, fraction V (Serva).…”

“…Isolated vacuoles of the yeast Saccharomyces pastorianus accumulate citrate and a-ketoglutarate. This transport is ATP-dependent and provided by the membrane potential (positive inside) (Kulakovskaya et al, 1991). It is not clear, however, if the tonoplast has transport systems for each organic acid and what their function is.…”