Table 1 

 Rates of Flow of Carbon through Active Pools of Amino Acids 



Calculated rate Equiv. NH4"'" 

 of synthesis R, uptake, Mmoles 

 Compound jumoles of carbon of NH4"'" 



* Not included in totals. 



b 



Figures are for carbamyl carbon only. 



derived, for the most part, from the listed amino acids. How- 

 ever, the aromatic rings of the amino acids are synthesized by 

 another pathway. 



In Table 1 we compare the rates of synthesis of carbon 

 skeletons that have been measured with the rate of uptake 

 of NH4 + . The rate of synthesis of any given amino acid 

 does not necessarily represent the rate of incorporation of 

 inorganic nitrogen into that amino acid, since it could be 

 formed by transamination from another amino acid. How- 

 ever, the total of the rates of synthesis of all "primary" amino 

 acids should account for the major fraction of the rate of 

 uptake of ammonia. By "primary" amino acids we mean 

 those amino acids whose carbon skeletons are not synthesized 

 from some other amino acid. Alanine, serine, and aspartic 

 acid are clearly primary amino acids, since their rates of 

 labeling reach a maximum as soon as the intermediates in 



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