The Metabolism of Amides in Green Plants* Iii. the Mechanism of Amide Synthesis

The explanation of the formation of amides in green plants is one of the oldest problems of plant biochemistry. Since the discovery in 1806 of asparagine in asparagus shoots by Vauquelin and Robiquet (1) and the demonstration in 1848 by Piria (2) of the derivation of this substance in seedlings from the proteins of the seeds and of its chemical relationship to malic acid, asparagine and its later discovered homologue glutamine (3) have been repeatedly investigated. Schulze (4) in 1898 expressed the view that these substances arise in seedlings from the reaction of ammonia, derived from the amino acids of the seed protein, with nitrogen-free nutrients, and that they serve as easily transportable substances eminently suited to provide nitrogen for protein regeneration in the growing parts of the plant. Prianischnikow and Schulow (5) in 1910 first suggested that an important function of the amides was to provide a means for the disposal of ammonia which otherwise might accumulate in high concentration and prove toxic. This idea was later developed in considerable detail (6, 7) and was supported by remarkably able experimentation with seedlings grown in nutrient solutions that contained ammonia ((8) pp. 762-767). Schulze’s view that the carbon compound which combines with ammonia to form the amide has its origin from carbohydrates was given direct support by the pioneer work of Suzuki (9) with fully developed plants and the extensive labors of Prianischnikow with seedlings confirmed this assumption, but the details of the