Phosphate Turnover and Pasteur Effect 268 



the fact that it makes no difference whether the yeast cells 

 are kept aerobically or anaerobically. Obviously the perme- 

 ability of the cell membrane, which could control the sugar 

 uptake, is independent of the gas phase. 



The peculiar form of the curve may be expressed by two 



TOO 800 ' 900 1000 

 glucose cone. (^g/mJ.) 



Fig. 5. Comparison of uptake of glucose, fructose and mannose; 



aerobic. 

 Experimental conditions as for Fig. 4. 



straight lines with different slopes (Figs. 4, 5). This suggests 

 that two processes overlap when glucose enters the yeast cell. 

 One process is probably an "active" transport and dominates 

 in the range of small substrate, concentrations from zero up to 

 0-001 M glucose. Under the conditions of the experiments this 

 mechanism can transport up to 5 [xmoles per minute per g. of 

 wet yeast cells, which amounts to nearly half the saturation 

 value. A second and much slower process is superimposed on 

 the first one and can be assumed to be the passive sugar 



