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TEXTBOOK OF PLANT PHYSIOLOGY 



Alanine 



Leucine 



Proline 



Phenyl alanine 



Tyrosine 



Aspartic acid. 

 Glutamic acid. 



Arginine 



Lysine 



Histidine 



Ammonia 



Legumins 

 of Peas 



2.08 

 8.00 

 3.22 

 3.75 

 1.55 

 5.30 

 16.97 

 11.71 

 4.98 

 1.69 

 2.05 



Phaseolin 



of Kidney 



Beans 



1.80 

 9.65 

 2.77 

 3.25 

 2.84 

 5.24 

 14.54 

 4.89 

 4.58 

 2.62 

 2.06 



Gliadin 

 of Wheat 



2.00 

 5.61 

 7.06 

 2.35 

 1.20 

 0.58 

 37.33 

 3.16 

 0.0 

 0.61 

 5.11 



Edestin 

 of Hemp 



3.60 



20.90 



1.70 



2.40 



2.13 



4.50 



14.07 



14.17 



1.65 



2.19 



2.28 



All of these amino acids are obtained from proteins through 

 hydrolysis, apparently without any great changes in the structure 

 of the molecule, which leads to the belief that they are linked to 

 each other in such a way that the COOH group of one acid unites 

 with the NH2 group of another. It must be remembered that 

 amino acids are amphoteric compounds, able to react as weak 

 acids and as weak bases at the same time. As a result of such 

 unions, there accumulates in the protein molecule a number of 

 CO — NH — CH groups which are the ones that give the biuret test. 

 An amino acid by itself will not give this reaction. 



Basing his work upon these suppositions, Emil Fischer (1906), 

 attempted to bring about a synthesis of the protein molecule. 

 Binding together amino acids, first by twos, then by threes, and 

 finally as many as 18 or 19, he obtained complex compounds named 

 by him polypeptides, which gave the biuret reaction and, in gen- 

 eral, possessed many of the properties of proteins. The structure 

 of the polypeptide may be represented by the following chain 

 formula : 



-NH-CH-CO-NH-CH-CO-NH^CH-CO-NH-CH-CO, 



Ri 



R2 



Ra 



R4 



where Ri, R2, etc. are parts of different amino acids, connected 

 with the link CH of the main chain to form lateral chains. Accord- 

 ing to the theory of Emil Fischer, actual proteins represent nothing 



