W. YEMM 



than the total requirement and there is every indication that the carbon skeletons 

 for the syntheses of the amino-acids and amides are provided in this way. 



Data obtained from similar experiments with yeast are summarized in Table II. 

 In the yeast a much more active synthesis of amino-acids and proteins occurs, but 

 here again there is evidence that this, together with the respiratory losses, is mainly 

 met by the breakdown of the reserve carbohydrates, glycogen and mannans. Other 

 sources of carbon in the cell are drawn upon to a less extent; measurements of the 

 respiratory quotient suggest that this may be from fat reserves. There are several 

 other points of interest in these records: they show, for example, the very great drain 

 on the reserves associated with nitrogen assimilation so that the diversion of carbon 



Table II 



Carbon balance sheet for yeast 



Aerated cultures allowed to assimilate for 

 2 hours in o 01 m NH 4 H 2 P0 4 at 25 C. 



Products mg. C/i gm. Yeast 



(1) Respiratory CO a 59 



(2) Syntheses 



Glutamine 2-2 



Glutamic acid 1 • 1 



Alanine 05 



Other sol. N 19 



Protein 6 6 



to the synthesis of amino-acids, amides and proteins is several times greater than that 

 lost as carbon dioxide. 



To sum up, the chief results of these analytical experiments indicate that the form- 

 ation of glutamic acid and its amide, glutamine, occurs in the first phases of nitrogen 

 assimilation in both yeast and root tissues. The synthesis is associated with high rates 

 of cell oxidation and is sustained by the mobilization of carbohydrate and possibly 

 other reserves in the cells. 



THE METABOLISM OF GLUTAMINE 



A close coupling between the formation of glutamine and the metabolism of carbo- 

 hydrates may be inferred from the enzymic mechanisms associated with the synthesis 

 of the amide. It is highly probable that glutamic acid arises in the cell by reductive 



58 



