SECTION I. 



THE CHEMICAL COMPOSITION OF THE PROTEIN MOLECULE. 



Hydrolysis. 



IT has been already stated that the method of hydrolysis is the only 

 one which has contributed to our present knowledge of the chemical 

 composition of the proteins, and that the hydrolysis has been effected 

 by (i) boiling with acids, (2) boiling with alkalies, (3) the action of 

 proteoclastic enzymes. 



Hydrolysis by the action of proteoclastic enzymes is never complete. 

 The earlier investigators always observed that a complex body anti- 

 peptone resistant to the further action of the enzyme was formed. 

 Fischer and Abderhalden have confirmed this observation and have 

 found that the resistant body contains all the phenylalanine and proline 

 present in the protein molecule ; even by the combined action of pepsin 

 and trypsin, although phenylalanine and proline are formed under 

 these conditions, a body resistant to enzyme hydrolysis still remained. 

 Almost complete hydrolysis may be effected by trypsin and the 

 enzymes in the small intestine if a sufficiently long time be given for 

 the digestion. Hydrolysis by enzymes, though of use in the discovery 

 of new units in the protein molecule, is not serviceable for a complete 

 analysis of the decomposition products. 



Hydrochloric acid, sulphuric acid, and hydrofluoric acid are the 

 acids which have been used in hydrolysis, caustic soda and baryta the 

 alkalies. 



Several observers have maintained that the results obtained by 

 hydrolysing with concentrated hydrochloric acid and 25-33 P er cent, sul- 

 phuric acid are different, but recent investigations by Abderhalden 

 and Funk, Skraup and Turk and others have shown that complete 

 hydrolysis is effected by both acids, if the boiling be continued for a 

 sufficiently long time. It is customary to boil with hydrochloric acid 

 for six to twelve hours, with sulphuric acid for twelve to twenty hours, 

 and to ascertain if the hydrolysis is complete by performing the biuret 

 test on the solution and on the residue which always remains when the 



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