692 SCIENCE PROGRESS 



any tyrosine or tryptophane. The alcohol-soluble vegetable 

 proteins are characterised by their complete lack of glycine 

 and lysine, and are especially rich in glutaminic acid (gliadin 

 of wheat containing 36 per cent.). Some animal proteins, such 

 as the protamines, yield enormously high percentages of 

 arginine (salmine = 84 per cent.). It is worth noting in this 

 connection that in the hydrolysis of all important proteins 

 which play the chief part in animal or vegetable metabolism, 

 all these amino acids occur almost without exception, so that 

 the conclusion must be drawn that none of them can be 

 dispensed with in organic life. 



Synthesis. — The study and isolation of the hydrolytic cleavage 

 products have thus been shown to be of the greatest importance. 

 As the same substances are not only formed by the action of 

 acids and alkalies, but also by the agency of the digestive 

 enzymes, they are to be regarded as the true " Bausteine " 

 (building stones), of which the complicated protein molecule is 

 built up. Starting from this idea E. Fischer has been able to 

 build up, by linking together simple amino acids (a process the 

 reverse of hydrolysis), substances which he called polypeptides. 

 These are very similar to the polypeptides which he isolated 

 from digestive mixtures, and even some of the relatively simple 

 ones, such as 1-leucyl-triglycyl-l-tyrosine, exhibit many of the 

 properties of the albumoses. The octa-deca-peptide derived 

 from fifteen molecules of glycine and three molecules of 

 leucine, having the high molecular weight of 121 3, is a sub- 

 stance which, in its external properties, closely resembles many 

 natural proteins. More than one hundred of these artificial 

 polypeptides have already been synthesised, and we may expect 

 in the near future the announcement of the synthesis of what 

 E. Fischer regards as the simplest protein, namely silk-fibroin, 

 which according to his researches only contains four different 

 amino acids. 1 



Classification of Vegetable Proteins. — The classification of the 

 proteins in general is at present under revision, and can only be 

 a provisional one in view of the rapid progress being made 

 in their chemistry. It is possible that shortly the increased 

 knowledge of the cleavage products and their quantitative 



1 For a complete account of Fischer's work see his book, Untersiichnngen 

 iiber Aminosauren, Polypeptide und Proteine, 1906 ; also R. H. Aders Plimmer, 

 Science Progress, vol. ii. 1907, 88. 



