260 Biological Chemistry. 



it will be obvious that several peptide linkages exist (in* 

 dicated in the above formula by dotted lines), at which 

 positions hydrolysis can take place 

 R* R B 



NH-CH-CO-NH-CH-CO- + H.O 

 C6*> R B 



= .^NH-CH COOH + NH 2 CH CO 



Theoretically it is conceivable that hydrolysis can occur 

 at any one or more places. A peptide linkage can be 

 broken either at the end of the chain or at any inter- 

 mediate point. By incomplete hydrolysis it is possible, 

 therefore, that a very large number of products can be 

 obtained from a complex protein made up by the conjuga- 

 tion of a large number of amino-acids. Several poly- 

 peptides are, therefore, derivable by the incomplete hydro- 

 lysis of a protein in addition to simple amino-acids. In 

 practice it is found that when a protein is digested with 

 gastric juice in acid solution at 37, many products are 

 obtained, varying in complexity from simple amino-acids 

 to highly complex substances, which, like the original 

 proteins, are incapable of passing a parchment membrane 

 (see p. 234). Up to the present it has been found im- 

 possible to separate such digestion products from one 

 another in a pure state. Those products which can be 

 precipitated from solution by the addition of salts are 

 known as proteoses (or albumoses), whereas the products 

 which cannot be thus precipitated, but which are precipit- 

 able by phosphotungstic acid and other similar reagents, are 

 known as the peptones. The salts generally employed for 

 the precipitation of the proteoses are ammonium sulphate 

 and zinc sulphate (which is employed in solutions made 

 acid with sulphuric acid). Some of the albumoses are 



