THE PARTICIPATION OF PHOSPHATE IN THE FORMATION OF A "CARRIER" FOR THE TRANSPORT OF MG(++) AND MN(++) IONS INTO YEAST CELLS

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 pretreated 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 pyruvate has little effect. Inhibitor studies with sodium acetate, redox dyes, and arsenate, reveal parallel effects on Mn(++) absorption, and on phosphate absorption. It 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.