66 PHYSIOLOGICAL CHEMISTRY. 



regarding the final products of the protein decomposition and 

 demonstrating that amino acids were the ultimate results of the 

 various forms of decomposition, these investigators, and notably 

 Fischer, set about in an effort to form, from these amino acids, by 

 synthetic means, substances which should possess protein character- 

 istics. The simplest of these bodies formed in this way was synthe- 

 sized from two molecules of glycocoll with the liberation of water, 

 thus: 



CH 2 - NH 2 - co IOHTH! HN - cn 2 - COOH. 



The body thus formed is a dipeptide, called glycyl-glycine. In an 

 analogous manner may be produced leucyl-leucine , through the 

 synthesis of two molecules of leucineor leucyl-alanyl-glycine through 

 the union of one molecule of leucine, one of alanine, and one of 

 glycocoll. By this procedure Fischer and his pupils have been able 

 to make a large number of peptides containing varied numbers of 

 amino acid radicals, the name polypeptides being given to the whole 

 group of synthetic substances thus formed. The most complex poly- 

 peptide yet produced is one containing fifteen glycocoll and three 

 leucine residues. 



Notwithstanding the fact that most synthetic polypeptides are 

 produced through a union of amino acids by means of their imide 

 bonds, it must not be imagined that the protein molecule is con- 

 structed from amino acids linked together in straight chains in a 

 manner analogous to the formation of simple peptides, such as 

 glycyl-glycine. The molecular structure of the proteins is much too 

 complex to be explained upon any such simple formation as that. 

 There must be a variety of linkings, since there is a varied assort- 

 ment of decomposition products of totally different structure. 



Many of these synthetic bodies respond to the biuret test, are 

 precipitated by phosphotungstic acid and behave, in other ways, 

 as to leave no doubt as to their protein characteristics. For instance, 

 a number of amino acids each possessing a sweet taste have been 

 synthesized in such a manner as to yield a polypeptide of bitter 

 taste, a well known characteristic of peptones. From the fact that 

 the polypeptides formed in the manner indicated have free acidic 

 and basic radicals we gather the explanation of the amphoteric 

 character of true proteins. Fischer expresses the encouraging 

 belief that he will soon be able to produce a true protein by the 

 synthesis of. its decomposition products. Silk fibroin is the protein 

 substance he expects to synthesize. He no doubt will perform this 



