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THE AMERICAN NATURALIST [Vol. XLV 



succeeded in securing- linkages of certain ones of these, 

 thus producing polymeric amino-acid compounds called 

 by Fischer polypeptids. Bodies of this same type have 

 been isolated from natural organic substances. These 

 polypeptids resemble peptones in appearance and, 

 moreover, they react in the same way peptones do 

 toward enzymes and various test reagents. One of the 

 artificially synthesized polypeptids, furthermore, is ap- 

 parently identical with one of the known polypeptids 

 found in digestion, and Z-leucyhtrigiycyl-/-tyrosin, when 

 prepared artificially, seems to have all the properties of 

 the albumoses. 



The amino-acids possess both acid and basic proper- 

 ties. It is this amphoteric condition that renders link- 

 age possible. The individual amino-acids which consti- 

 tute the units in such polymerizations are frequently 

 spoken of as " nuclei." Linkage has been obtained not 

 only between similar "nuclei," but also between "nuclei" 

 of different amino-acids. 



The results point clearly to the conclusion that the 

 peptones and higher proteins are huge molecules formed 

 chiefly of amino-acid molecules linked together by NH 

 and CO affinities left unsatisfied as a result of processes 

 comparable to dehydration. Such a protein molecule 

 may perhaps be represented as a main chain or ring, of 

 which the respective links are amino-acid "nuclei." 

 Glycocoll, NH 2 CH 2 COOH, for instance, would through 

 dehydration have for its nucleus in such a chain 

 — NH.CH 2 .CO— . Furthermore, since one H of the CH 2 

 of such "nuclei" 



( e . g . f _NH.CH.CO-) 



H 



can be substituted by various compounds (acetic acid, 

 buthane, methylparaoxybenzene, etc.) we are led to con- 

 clude that to each link of the protein chain, a side-chain, 

 differing in constitution in different cases, is attached 

 or is attachable by replacement of this hydrogen atom. 

 The well-known instability of living protein would seem 



