Originally published in Acta Physiol. Scand. 2, 347 (1941). 



96. POTASSIUM INTERCHANGE IN YEAST CELLS 



G. Hevesy and N. Nielsen 



From the Institute of Theoretical Physics and the Carlsberg Laboratory 



cf Copenhagen 



Using ladiophosphorus as an indicator, phosphate present in the yeast 

 cells was found to interchange very slowly with the phosphate of the 

 nutrient solution (Hevesy, Linderstr0m-Lang and Nielsen, 1937). 

 Recently, we extended this investigation to the behaviour of potassium, 

 using radiopotassium (*'^K) as an indicator. In this note, experiments 

 on the uptake and release of radiopotassium by the yeast cells are 

 communicated. 



EXPERIMENTAL PROCEDURE 



The yeast used in our experiments has been grown for three to five days in 

 beerwort at 25°. A pure yeast culture was applied. The yeast was separated by 

 centrifuging and was purified by repeatedly suspending it in water and centrifuging 

 the suspension. The suspension finally obtained, contained yeast corresponding 

 to a dry substance weight of 1.5 gm per 100 cm^. 



The nutrient solution (pH = 4.5) had the following composition: 1.4 gm 

 MgSO^-THjO; 2.0 gm NaH2P04: 1.0 gm KCl; 0.8 gm CaClj • 6 H^O; 1.2 gm 

 (NH4)2S04; 0.01 gm FeCls • 6 HgO; 100 gm sachaiose; 0.2 y biotin; 100 y aneurin; 

 2 mgm /5-alanin; 2.0 gm citric acid per liter. The KCl was replaced by labelled 

 KCl in those cases in which the intiusion of ^^K from the nutrient solution into 

 the yeast cells was investigated. 



At the start of the experiinent, 1 volume yeast suspension was mixed with 

 1 volume nutrient solution. The dry substance of the yeast was determined in 

 the usual way by filtering the suspension through a glass filter (1 G 4 Schott) 

 and by drying the yeast at 105°. The potassium content of the yeast and the 

 nutrient solution was determined by the method of Winkel and Maas (1936) 

 respectively Kolthoff and Bendix (1939). The samples analysed contained 

 10—20 mgm potassium. The yeast suspended in nutrient solution was shaken 

 in a thermostat kept at 25°. The samples taken at intervals were sharply centri- 

 fuged; the 3' were not washed before analysis in older to prevent loss of potassium 

 by the yeast. 



In some of our experiments, the KCl content of the nutrient solution was 

 replaced by labelled potassium chloride; in other experiments, yeast containing 

 labelled potassium was placed in a non-radioactive nutrient solution. The labelled 

 potassium chloride was prepared by bombarding KCl with deuterons accelerated 



