24: THE AMINO ACIDS 



acid may show very wide variations being present to 

 the extent of nearly 44 per cent in wheat gliadin where- 

 as gelatin contains less than 1 per cent. Tryptophane 

 may be absent as in zein and gelatin. Arginine shows 

 great variation being present in largest quantity in the 

 protamines (salmine). On the other hand, lysine is 

 absent in salmine as well as in zein. In the protamine, 

 salmine, histidine is not present but may be isolated 

 from all other examples of simple proteins shown here. 

 It is clear that in general the various proteins are made 

 up of the same units and it undoubtedly follows that 

 the individual protein characteristics are bestowed by 

 the relative proportion of the units or by their absence. 

 In the tables given it will be observed that in most 

 instances the total amino acids fall far short of the 

 theoretical yield, a deficit of 40 to 50 per cent being in 

 order. Previously it has been assumed that only a 

 portion of the amino acids was known. At present, 

 however, it seems very probable that the deficit is to 

 be explained on the hypothesis of inadequate methods 

 of analysis. 



SYNTHETIC PROOF OF THE STRUCTURE OF PROTEIN 



Since the time of Liebig it has been assumed that 

 the protein molecule consisted of a huge complex of 

 amino acids linked together in some unknown manner. 

 There are many possibilities for such combinations 

 and certain of them have been subjected to experimen- 



