THE EFFECT OF POTASSIUM IONS ON THE ABSORPTION OF ORTHOPHOSPHATE AND THE FORMATION OF METAPHOSPHATE BY BAKERS' YEAST

Abstract

Jeener and Brachet (1) found that the absorption of inorganic phosphate by bakers' yeast is greatly enhanced when the incubation of the yeast in a phosphate-containing nutrient (period of P absorption) is preceded by a period of incubation in a medium devoid of phosphate (period of P starvation).The Belgian authors had already demonstrated that a large part of the absorbed phosphate appears in the yeast cells as a compound which is different from orthophosphate.Wiame (2, 3) and independently Schmidt, Hecht, and Thannhauser (4) characterized this compound as a metaphosphate.Observations concerning the occurrence of metaphosphate in yeast and molds have previously been reported in the literature.Kossel ( 5) and Ascoli (6) found in the nucleic acid fraction of yeast a compound resembling metaphosphate.More than 40 years later MacFarlane (7) conclusively identified this substance as a metaphosphate.Mann (8) isolated a metaphosphate from Aspergillus.The rates of phosphate assimilation by bakers' yeast are little affected by varying the pH values of the medium between 4 and 7.5 or by varying the phosphate concentrations between 0.002 and 0.1 M. Variations of the mutual proportions of the cations as well as the complete omission of sodium and magnesium salts during the period of phosphate absorption likewise had little influence on these processes.It was found, however, that the absorption of orthophosphate and the formation of metaphosphate by the yeast were strongly inhibited in media which were devoid of potassium salts.In the present paper, we will describe experiments in which this effect of potassium deficiency was studied.EXPERIMENTAL