PROTEINS. 113 



Secondary Protein Derivatives. 



These derivatives result from a more profound cleavage of the 

 protein molecule than that which occurs in the formation of the 

 primary derivatives. The class includes proteases, peptones and 

 pep tides. 



PROTEOSES AND PEPTONES. 



Proteoses are intermediate products in the digestion of proteins 

 by proteolytic enzymes, as well as in the decomposition of proteins 

 by hydrolysis and the putrefaction of proteins through the action 

 of bacteria. Proteoses are also called albumoses by some writers, 

 but it seems more logical to reserve the term albumose for the 

 proteose of albumin. 



Peptones are formed after the proteoses and it has been cus- 

 tomary to consider them as the last product of the processes before 

 mentioned which still possess true protein characteristics. In other 

 words it has been considered that the protein nature of the end- 

 products of the cleavage of the protein molecule ceased with the 

 peptones, and that the simpler bodies formed from peptones were 

 substances of a different nature (see page 63). However, as the 

 end-products have been more carefully studied, it has been found 

 to be no easy matter to designate the exact character of a peptone 

 or to indicate the exact point at which the peptone characteristic 

 ends and the peptide characteristic begins. The situation regarding 

 the proteoses, peptones and peptides, is at present a most unsatis- 

 factory one because of the unsettled state of our knowledge regard- 

 ing them. The exact differences between certain members of the 

 peptone and peptide groups remain to be more accurately estab- 

 lished. It has been quite well established that the peptones are 

 peptides or mixtures of peptides, but the term peptide is used at 

 present to designate only those possessing a definite structure. 



There are several proteoses (protoproteose, heteroproteose and 

 deuteroproteose), and at least two peptones (amphopeptone and 

 antipeptone), which result from proteolysis. The differentiation 

 of the various proteoses and peptones at present in use is rather 

 unsatisfactory. These compounds are classified according to their 

 varying solubilities, especially in ammonium sulphate solutions of 

 different strengths. The exact differences in composition between 

 the various members of the group remain to be more accurately 

 established. Because of the difficulty attending the separation of 

 these bodies, pure proteose and peptone are not easy to procure. 

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