Lecture 6 



— 141 — 



Biochemical Problems 



COOH 



a-keto-glutaric acid, gg^ , glutamine. In some plants 



CH2 



COOH 



asparagine is the principal amide and in others gluta- 

 mine. It is doubtful that most plants synthesize ex- 

 clusively either asparagine or glutamine. A metabolic 

 cycle that may explain the formation of either or both 

 amides is one known as the citric acid cycle, which in 

 one of its forms is illustrated by Fig. 39. Far more 

 remains to be learned of the nature of the respiratory 



+ H20 



+ H20 



Textfigure 40. — Scheme of synthesis of asparagine and 

 glutamine from amino acids. 



processes in plants, and of the specific metabolic re- 

 actions that eventuate in amide synthesis. The degree 

 to which the formation of the organic acid precursors 

 may be stimulated by ammonia requires further eluci- 

 dation. There are also to be explained the steps in 

 synthesis that make possible the foiTnation of the 

 array of amino acids required for the building up of 

 proteins. 



