258 Biological Chemistry. 



Part III. (B) The Derived Proteins. 



It has been already stated that the proteins on com- 

 plete hydrolysis yield a mixture of amino-acids. If less 

 drastic methods are adopted, intermediary products can 

 be obtained which contain several amino groups coupled 

 together in the form of polypeptides (see p. 228); the 

 latter on complete hydrolysis undergo scission and yield 

 a mixture of amino-acids. The production of such inter- 

 mediary products of hydrolysis may be compared with the 

 production of substances like the dextrins and maltose 

 from starch. The last-named substance on complete hydro- 

 lysis yields only dextrose, but if treated with certain 

 ferments, such as diastase, the hydrolysis is incomplete; 

 a scission of only a certain number of the dextrose groups 

 coupled together in the original starch molecule takes 

 place, and a residue can be obtained which is less complex 

 than the parent substance, but which still contains in the 

 molecule two or more dextrose groups. (Compare p. 215.) 



If proteins are treated with certain ferments or with 

 acids at lower temperatures (for example, at 37 and not 

 boiled with the acids, as is usual when complete hydro- 

 lysis is desired) the scission of amino-acids is not com- 

 pleted ; by variation of conditions of hydrolysis, substances 

 of greater or lesser complexity can be obtained according 

 to the method employed. All such substances, on more 

 drastic hydrolysis, can be degraded into their constituent 

 amino-acids by a method similar to that by means of 

 which dextrin or maltose, the intermediary hydrolysis 

 products of starch, can be degraded into dextrose. The 

 intermediary hydrolysis products from proteins are, like 

 the parent substance, essentially polypeptides, although of 

 smaller complexity. Of the intermediary hydrolysis pro- 

 ducts very few have been obtained in a crystalline form. 



