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F. Lynen, et al. 



(Lynen, 1941). It was found that the concentration of in- 

 organic phosphate under oxygen was lower than under nitro- 

 gen. If yeast cells are suspended in glucose solution and shaken 

 alternatively under oxygen and nitrogen, the free phosphate 

 oscillates between the lower aerobic and the higher anaerobic 

 level (Fig. 2). However, the differences observed do not seem 

 to be large enough to explain the considerable slowing down 



Fig. 2. The orthophosphate content of baker's yeast, 



aerobically and anaerobically. 



Yeast, 10 per cent ; glucose, 6 per cent ; under oxygen and 



nitrogen alternatively; temp. 30°. 



of triose phosphate dehydrogenase caused by respiration. In 

 an attempt to overcome the difficulty, we considered the 

 possibility of some of the inorganic phosphate in the cell, as 

 determined by the molybdenum blue method, being present 

 not as free phosphate, but as having existed as some labile 

 phosphorus compound, e.g. acyl phosphate, which had 

 become hydrolysed during assay (Lynen, 1941; Kamen and 

 Spiegelman, 1948). More recent observations and the negative 

 result of attempts to find noticeable amounts of acyl phosphate 

 in respiring or fermenting yeast cells (Holzer, 1949) made it 



