Phosphate Turnover and Pasteur Effect 271 



proposed by Chance and Williams (1956), that ADP controls 

 the fermentation rate. The decrease of fructose diphosphate 

 to the aerobic level shows a lag period and seems to reflect the 

 low cytoplasmic orthophosphate concentration remaining 

 available for fermentation under the aerobic conditions. 



The behaviour of glucose-6-phosphate needs further ex- 

 planation. In the experiments cited above, it was also found 



t{ 



It 



N2 



-5 



•4 



02 



-7--P 



■Po 



■ATP 



■ADP 





 min 



Fig. 11. Changes in the inorganic and organic phosphates of baker's 

 yeast accompanying the transition from fermentation to respiration. 

 Yeast, 10 per cent; glucose, 2 per cent; in 0-02 m citrate buffer, pH 

 5-4; temp. 15°; under nitrogen; oxygenated at zero time by bubbling 

 oxygen through the yeast suspension. The ordinate values refer to 

 changes in concentration of compounds specified. 



that the steady-state level of glucose-6-phosphate is higher 

 under aerobic than under anaerobic conditions. Two different 

 explanations fit such an experimental finding: (i) a faster 

 formation of the intermediate Jn the reaction chain, or (ii) a 

 slower consumption. The first mechanism is not involved 

 here. As pointed out already, one of the main features of the 

 Pasteur effect is the lowered phosphorylation of glucose in 

 respiring cells. Thus, the only remaining possibility is that the 

 further transformation of glucose phosphate is diminished. As 



