146 



PHYSIOLOGY OF NUTRITION 



I. Monoamino ' 

 acids 



Wheat 



Glycin o • 9° 



Alanin 4-6s 



Serin " • 74 



Leucin 6 . 00 



Aspartic acid 0.90 



Glutamic acid 23 -40 



Phenyl alanin ■'■oo 



Tyrosin 4^ 25 



Cystin^ o-oz 



Total 42-86 



Oats 



I Lysin. 



1.90 



2. Diamino i Arginin 4-7° 



acids [ Total 6.60 



3. Heterocylic 

 compounds 



Histidin i.76 



Prolin 4- 20 



Tryptophan trace 



Total 5-96 



IS 



4 



18 



3 



I 



45 



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 buUding- stones out of which proteins 

 are formed, Emil Fischer^ 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 polj^^eptides. 

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

 ciated in their formation as dipep tides, tripep tides, 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.^ 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. 



' Fischer, Emil, Untersuohungen iiber Aminos&uren, Polypeptide und Proteine. Berlin, 1906. Ab- 

 derhalden, 1909. [See note 2, p. 144.] 



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

 Ber. Deutseh. Chem, Ges. 39^: 7S2-760. 1906. Idem, Bildung von Dipoptiden bei der Hydrolyse der 



Proteine. Ibid, 39^^ : 2315-2320. 1906. 



f Cystin is a diamino acid. — Ed. 



Idem, same title. Ibid, 40 : 3544-3562. 1907, 



