T H E Participation of Phosphate in T H E Formation of a "carrier" for T H E Transport of Mg ++ and Mn ++ Ions into Yeast Cells* by D. H. Jennings, $, § D. C. Hooper, An~

During the absorption of phosphate by yeast, the cells acquire the capacity to absorb Mn ++ and Mg ++, a capacity which is retained even after phosphate is no longer present in the medium. Cells pretrcated with phosphate and then washed, slowly lose their ability to absorb Mn ++, the rate of loss depending on the temperature and on the metabolic state. The fermentation of sugars induces a very rapid loss of absorptive capacity, whereas the respiration of ethyl alcohol, lactate, or pymvate has little effect. Inhibitor studies with sodium acetate, redox dyes, and arsenate, reveal parallel effects on Mn ~" absorption, and on phosphate absorption. I t is concluded that the synthesis of a carrier for the transport of Mg ++ and Mn ++ involves a phosphorylation step closely coupled with reactions involved in the absorption of phosphate. Yeast cells in the absence of glucose bind bivalent cations to the cell surface (1). Cations so bound are completely exchangeable with the cations of the medium. Certain of these cations, particularly Mg ++ and Mn ++, can be specifically absorbed by yeast, in a non-exchangeable manner, provided that glucose is available and that phosphate is also absorbed (2). This cation absorption is stimulated by low concentrations of K +, but inhibited at higher concentrations. The inhibitory effect of K + is due to the accumulation of a large surplus of K + within the cell, whereas the stimulation of uptake at the lower concentrations is the result of the enhancement of phosphate accumulation (3). The rate of Mn ++ uptake is also conditioned by the concentration of phosphate; and, although the rate of uptake is never greater than the rate of * This work was aided in part by a grant from the Electro Metallurgical laboratory, a division of Union Carbide and Carbon Corporation, and in part is based on work performed under contract with the United States Atomic Energy Commission at The University of Rochester Atomic Energy Project, Rochester, New York. King George VI Memorial Fellow. § Present address: the Botany Department, Leeds University, England~