Lecture 6 — 139 — Biochemical Problems 



Whatever the source of inorganic nitrogen, we are 

 faced with the problem of the synthesis of amides and 

 amino acids, preceding the synthesis of proteins or 

 other complex nitrogen containing compounds. The 



COOH 



two principal amides formed are asparagine chT^' 



CONHj 

 COOH 



and glutamine 9^^^- t-. i- • j.- i.- 



cHi • Earlier mvestigations compre- 

 C0NH2 

 hensively surveyed by Chibnall and by Vickery 

 developed the view that these amides are sjmthesized 

 as a response to ammonia absorption and that they 

 act as a means of detoxication of ammonia. Later the 

 theory was advanced in Germany that plants with 

 markedly acid reactions of the sap can accumulate 

 ammonium organic acid compounds without injury 

 and that plants may be roughly divided, on the basis 

 of this distinction, into "amid" plants, with slightly 

 acid reactions, and "ammonia" plants, with markedly 

 acid reactions. 



These general concepts have had value in the study 

 of the nitrogen metabolism of plants, but the investiga- 

 tions of Vickery and his associates, and those of Chib- 

 nall, have made us aware that there are more funda- 

 mental considerations to be examined, and that these 

 rest on modern research in biochemistry. Much of 

 this research has originated in the work of biochemists 

 who have experimented with animal tissues, but in the 

 study of many phases of metabolism a useful transfer 

 of knowledge is possible in providing suggestions and 

 guidance, in the present status of knowledge of plant 

 metabolism. 



In the light of evidence now available, ammonia 

 would be expected to react with precursors derived 

 chiefly from carbohydrate metabolism; a cycle of 

 transfoiTnations occurs in an organic acid series to 

 provide these precursors. The suggestion is that from 



COOH 



oxalacetic acid, gg, , asparagine is formed and from 



COOH 



