164 



PHYSIOLOGY OF NUTRITION 



1. Monoamino 

 acids 



2. Diamino 

 acids 



Heterocylic 

 compounds 



Glycin. ....... 



Alanin 



Serin 



Leucin 



Aspartic acid . . 

 Glutamic acid. 

 Phenyl alanin. 



Tyrosin 



Cystin * 



Total 



Lysin. . 



Arginin . 



Total... 



Histidin. 



Prolin 



Tryptophan . 



Total 



Wheat 



0.90 

 4 65 

 0.74 

 6.00 

 0.90 

 23.40 

 2 .00 



4-25 

 0.02 



Oats 



596 



The greater part of the simple proteins is thus seen to be composed of mono- 

 amino acids. 



After numerous analyses had firmly established the fact that the various 

 amino acids are to be considered as the building-stones out of which proteins 

 are formed, Emil Fischer 1 took up the synthesis of these complicated substances 

 from the amino acids. We now know many compounds that are produced by 

 an amid-like linking of amino acids and Fischer has called these polypeptides. 

 These compounds are classified according to the number of amino acids asso- 

 ciated in their formation as dipeptides, tripeptides, tetrapeptides, pentapeptides, 

 etc. The simplest polypeptides are crystalline compounds, but the more com- 

 plicated ones, with great molecular weights, have colloidal properties, give the 

 biuret reaction and are similar to peptones. 



It is hardly to be doubted that Fischer's reasoning and methods point the 

 way to the synthesis of proteins. The partial hydrolysis of the simple proteins 

 has demonstrated the fact that polypeptides are undoubtedly concerned in the 

 building up of these substances. This partial hydrolysis is effected by acids 

 at room temperature or, at most, at temperatures not higher than 37°C. In this 

 way polypeptides may be obtained from various simple proteins. 2 It thus 

 appears that the simple proteins are to be considered as built up from poly- 

 peptides, which, in their turn, are products of amid-like linkings of various amino 

 acids. 



1 Fischer, Emil, Untersuchungen uber Aminosauren, Polypeptide und Proteine. Berlin, 1906. Ab- 

 derhalden, 1909. [See note 2, p. 162.] 



2 Fischer, Emil, and Abderhalden, E., Bildung eines Dipeptids bei der Hydrolyse des Seidenfibroins. 

 Ber. Deutsch. Chem. Ges. 39': 752-760. 1906. Idem, Bildung von Dipeptiden bei der Hydrolyse der 

 Proteine. Ibid. 39" : 2315-2320. Idem, same title. Ibid. 40" : 3544-3562. 1907- 



■^Cystin is a diamino acid. — Ed. 





