The Active Transport of Phosphate Into the Yeast Cell

Abstract

The exchanges of phosphate between cellular and intracellular compartments have been studied in a number of cell types. In each case the entry of phosphate into the cell seems to be associated with metabolic processes at the cell surface (1). For example, in red blood cells, the uptake of Pro-labelled phosphate is to a large measure dependent on glycolysis (2). It has a high temperature coefficient (3) and is blocked by metabolic inhibitors (2). Studies of precursor relationships and also of phosphate turnover in red cell stroma suggest that phosphate enters the cell by incorporation in the membrane into glycolytic intermediates such as 2,3-diphosphoglycerate and ATP (4, 5). In muscle, precursor relationships with 1 ~ also suggest that phosphate enters the cell v/a some phosphorylation reaction (6). However, the latter studies involve the technical difficulty of distinguishing extra-and intracellular orthophosphate in the muscle mass. Autoradiographic studies (7) lend support to the phosphorylation concept. In sea urchin eggs formation of ATP at the cell surface seems to be an integral part of the mechanism of phosphate entry (8).In microorganisms a dependence of phosphate entry on metabolic reactions is well established (9). Yeast has been most intensively studied. In growing yeast, the uptake of PS*-labelled phosphate requires the presence of sugar and is blocked at low temperature (10), and by metabolic inhibitors (9). The phosphate which is absorbed is largely converted to polymerized forms of phosphate (11,12). The total amount of uptake is dependent on the presence of cations such as potassium and magnesium which are also absorbed (13). It is not clear whether the effect of potassium is due to a stimulation of the entry process for phosphate, or to a maintenance of cation-anion balance within the cell, or to stimulation of metaphosphate formation within the cell.In the present study some of the properties of the process of phosphate entry into yeast cells have been investigated, including the kinetics of the reaction, the nature of the substrate, the nature of the entering ion, the effect of potassium, and certain other related phenomena.

The Coupling of Phosphate Accumulation to Acid Production by a Non-growing Streptococcus

“…By contrast, when SL-I cocci were harvested and stored at the pH values to be tested, phosphate accumulation rates were strongly pH dependent. This finding is similar to those observed with Staphylococcus aureus (Mitchell, 1954) and yeast (Goodman & Rothstein, 1957). These observed variations of phosphate uptake rate with extracellular pH, at least with SL-I, may be due to disruption of the phosphate accumulative machinery incurred when energy-depleted cocci are faced with disadvantageous environmental pH for a prolonged period of storage.…”

Interaction of cations with phosphate uptake by Saccharomyces cerevisiae. Effects of surface potential

“…Since phosphate is taken up as the univalent anion only (Goodman & Rothstein, 1957) and at pH7.2 only 20% of the phosphate is in this form, an appropriate correction was made. The data are also corrected for complex-formation between phosphate and Mg2+ [about 23 % of the phosphate is complexed by Mg2" under these conditions (Kobos 1979& Rechnitz, 1976].…”

Entry of phosphate into yeast cell

“…The maximum site increase is in the absence of glucose (fig 7). The component of phosphate uptake N-ith K,,, (6) and would have been greatly predominant in some of their experiments. Neither iodoacetate nor barbital apparently inhibits the reaction at concentrations of 10-1 M, although precision is so low that a one and a half-fold change would be uncertain (figs 4 & 5).…”

“…Particular attention has been devoted to the esterification of phosphate in this process and to the nature of coupling with a source of energy. The accumulation of phosphate has been considered as coupled to: A, the general reactions of glycolysis (10); B, the action of glyceraldehyde-3-phosphate dehydrogenase (6,16); C, a redox pump (4,5) and D, oxidations in the respiratory chain under aerobic conditions (14).…”