THE CHEMISTRY OF THE PROTEINS 105 



not complete. Even on prolonged action, when the biuret re- 

 action is absent or only very faint, a complex product together 

 with amino acids results. This complex polypeptide, as it is 

 termed, contains the whole of the proline and phenylalanine 

 contained in the protein, together with other amino acids. 

 It is apparently not identical with Kiihne's antipeptone which 

 gave the biuret reaction. On complete hydrolysis by acid, it 

 yielded the same quantity of proline and phenylalanine as would 

 result from the protein by acid hydrolysis. 



In the animal body the action of trypsin is preceded by that 

 of pepsin. If a protein be first digested by pepsin and then by 

 trypsin, the same complex polypeptide might be expected to 

 result, but this was not the case. It was less in amount, and 

 did not contain the whole amount of the proline and phenylala- 

 nine of the protein, a certain portion of these being found with 

 the other amino acids, which had been split off. It would thus 

 appear as if the protein molecule contained a special nucleus, 

 as suggested by Kossel, who believes that it consists mainly of 

 the diamino acids ; these make up 90 per cent, of the pro- 

 tamine molecule, the protein molecule containing less of this 

 nucleus and more monoamino acids than the protamine. 

 Histones are a transition product between the protein and 

 protamine. Unfortunately, by the method adopted by Fischer, 

 a nucleus consisting mainly of diamino acids could not be 

 definitely determined, since the phosphotungstic acid used not 

 only precipitated the complex polypeptide, but also the diamino 

 acids, so that it was impossible to tell whether they were free 

 or combined together in this polypeptide. Subsequent work, 

 if attended with such far-reaching results, will certainly decide 

 this question, especially as less complex combinations of amino 

 acids have already been isolated from proteins. New amino 

 acids and oxyamino acids may still be discovered ; Skraup's 

 results point to the existence of two more diamino acids and 

 other oxy-amino acids ; their exact constitution is still very 

 uncertain. His work cannot be further mentioned here. 



The hydrolysis of various proteins has been carried out by 

 Abderhalden and several co-workers in the hope of being able 

 to obtain closer relationships between the members of the 

 various classes of proteins, and more distinctions between the 

 classes. Abderhalden's book on physiological chemistry brings 

 out these points as well as many others of great interest. 



