126 PHYSIOLOGY OF ALIMENTATION. 



he products formed are due to the action of alkali-proteinase 

 alone and not to the action of intracellular enzymes exist- 

 ing beside the alkali-proteinase. 



The following is a list of the amino-acids that have been 

 isolated from various proteins. In spite of the great physi- 

 cal differences between the proteins obtained from different 

 sources, they are very similar in chemical constitution. When 

 any protein is split hydrolytically, be this under the influence 

 of alkali-proteinase or acid-proteinase, or as it is often accom- 

 plished in the laboratory, through the action of strong acids 

 or alkalies, the same series of simple substances is always ob- 

 tained which consists almost entirely of amino-acids. All 

 proteins, moreover, yield the same amino-acids, only the pro- 

 portion which these bear to each other in the different pro- 

 teins is different, and sometimes one or the other of the 

 acids may be entirely absent. In order to render what is to 

 follow more intelligible, the next paragraph contains a list 

 of the amino-acids which have been obtained not only through 

 the action of alkali-proteinase, but also by other methods of 

 hydrolysis. Most of these acids have, however, been isolated 

 from at least certain proteins through the action of alkali- 

 proteinase alone. It will be noticed that certain of those 

 enumerated have already been mentioned as products of 

 peptic digestion. 



Glycocoll, alanin, aminoisovalerianic acid, leucin, isoleucin, 

 serin, aspartic acid, glutamic acid, lysin, arginin, histidin, 

 cystin, phenylalanin, tyrosin, prolin, oxyprolin, tryptophan. 1 



The diamino-acids in the above series, such as lysin, arginin, 

 and histidin, are often spoken of as the hexone bases, and con- 

 titute with ammonia the basic products of the hydrolysis of 

 proteins. 



The following diagram, as arranged by ABDERHALDEN, may 

 serve to indicate the scheme according to which the proteins 

 are under the influence of a ferment (or other hydrolytic 



1 ABDERHALDEN. Lehrbuch d. physio! . Chemie. Berlin, 1906, p. 160. 



