Phosphate Turnover and Pasteur Effect 261 



yet, only the inhibition of glucose degradation via triose 

 phosphate has been considered. The Pasteur effect, however, 

 also becomes evident in the aerobic decrease of sugar uptake 

 by the cell. This can be demonstrated in a simple way by 

 suspending equal amounts of yeast cells in sugar solutions. 

 One sample is kept aerobically, the other anaerobically, and 

 both are assayed for the disappearance of glucose from the 

 medium. It is found that the glucose decreases more rapidly 

 with fermenting yeast cells than it does with respiring cells 

 (cf. Table II). 



Our experiments rule out the possibility that oxygen 

 changes the cell-wall permeability. If an effect of that kind 

 existed, we should expect the inter-relationship of sugar 

 uptake and sugar concentration in the medium to be different 

 under aerobic and anaerobic conditions. Hartmann (1958, 

 unpublished), in our laboratory, has studied this problem 

 systematically. Of course, his measurements had to be 

 restricted to low sugar levels where no Pasteur effect occurs. 

 The technique used was as follows: a mechanically driven 

 syringe delivers sugar solution at a constant rate into a large 

 volume of yeast suspension. At certain intervals the sugar 

 concentration of the solution is measured. Fig. 3 shows the 

 technical set-up. It was found that a constant sugar concen- 

 tration is maintained, which means that the addition of sugar 

 from the syringe and the uptake of the yeast cells correspond 

 to each other. By varying the sugar concentration of the 



