W. YEMM 



of barley and with food yeast, Torulopsis utilis. These materials were chosen because, 

 despite wide differences in general nutrition, they both have a high capacity for 

 assimilating nitrogen and synthesizing proteins from simple inorganic compounds 

 of nitrogen. For example, cultures of food yeast, supplied with ammonium salts under 

 favourable conditions, will double their protein content within 2-3 hours. High rates 

 of assimilation and protein synthesis also obtain in the early stages of development 

 of barley seedlings. The conditions which favour a rapid uptake of ammonium salts 



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Figure 1 . The effect of ammonium ions on the rate of oxygen 

 uptake of yeast. Replicate samples, containing 60 mg. of 

 fresh yeast, were treated at the time indicated with either 

 ammonium or sodium phosphate. Oxygen uptake was 

 measured by conventional manometric methods. 



or nitrate were investigated in a series of preliminary experiments and an account of 

 these has already been given (Folkes, Willis and Yemm, 1952; Yemm and Folkes, 

 1954). The chief results may be briefly recorded. 



An essential condition for rapid assimilation is a high level of readily available 

 carbohydrates in the cells. With both organisms this requirement can be met by 

 growing them for a short preliminary period under conditions of high carbohydrate 

 supply, but deprived of nitrogen. The seedlings were therefore grown at high light 

 intensities in a nutrient solution deficient in nitrogen. A similar effect is achieved 



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