Phosphate Uptake by Phosphate-Starved Euglena

Phosphate participates in an essential way in a number of cell functions, including glycolysis, oxidative phosphorylation, and nucleic acid synthesis. In almost all the cell types studied, the entry of phosphate seems to be controlled at the cell surface (1). In yeast, in which phosphate can be transported against a concentration gradient, the accumulation of phosphate depends on glycolysis and on the presence of cations such as potassium or magnesium (2) and is competitively inhibited by arsenate (3). In phosphate-starved yeast there is an increased level of acid phosphatase activity (4) and an increased rate of phosphate accumulation, but both Rothstein and Meier (5) and Borst Pauwels (6) have concluded that the acid phosphatases of yeast do not directly function in the uptake of phosphate. I t has recently been shown that Euglena gracilis synthesizes an induced acid phosphatase as growth ceases because of phosphate deprivation (7, 8) and acquires the ability to rapidly accumulate phosphate (8). In phosphate-deprived yeast it is probable that the increase in acid phosphatase activity occurs primarily in the region between the cell membrane and the cell wall (9, 10). In Euglena the induced enzyme is localized in specific helical regions of the cell surface (11). Because of these similarities it appeared that an investigation of phosphate accumulation by Euglena would contribute not only to our understanding of the physiology of this flagellate but also might be of interest from the comparative point of view. In this paper we present evidence concerning the effects of temperature, pH, cations, and several types of inhibitors on phosphate uptake in Euglena. 1 1 2 5 on July 6, 2017 jgp.rress.org D ow nladed fom I I 14 T H E J O U R N A L O F G E N E R A L P H Y S I O L O G Y • V O L U M E 4 9 • 1g66