SYNTHESIS OF PROTEINS 9 



4. The Synthesis of Proteins. — The marked predominance 

 of amino-acids in the products of protein hydrolysis, long ago 

 led protein chemists to surmise that the amino-acid structure, 

 or some derivative of that structure, must be represented in a 

 high degree in the protein molecule, and it was in following 

 this clue that Schiitzenberger (64) carried out one of the earliest 

 and most successful attempts to synthesize bodies of a protein 

 character. Recognizing that the decomposition of proteins into 

 amino-acids is essentially a phenomenon of hydrolysis, he re- 

 garded dehydration as an essential feature of any attempt at 

 protein synthesis, while the abundance of amino-acids among 

 the products of protein hydrolysis and the presence therein of 

 bodies related to urea, led him to believe that protein synthesis 

 must consist in the linkage of amino-acids with molecules of urea 

 and the elimination of water. Accordingly amino-acids were 

 mixed with urea and phosphorus pentoxide and heated to 125° C. 

 The product was a pasty solid, soluble in water and readily pre- 

 cipitated by alcohol. It was, furthermore, precipitated from aque- 

 ous solution by the usual protein precipitants and gave the biuret 

 and xanthoproteic reactions. 



This experiment of Schtitzenberger's left us, however, very- 

 much where we were, so far as real knowledge of the structure 

 of the protein molecule is concerned. The knowledge of the fact 

 that a mixture of amino-acids and urea yields, under certain 

 treatment, a body or bodies more or less closely resembling the 

 proteins, furnished us little or no information regarding the 

 structure of the protein molecule which we did not already 

 possess in the fact that the disintegration products of the pro- 

 teins are predominantly amino-acids. Prior to Schiitzenberger, 

 Grimaux (28) had shown that condensation-products of amino- 

 benzoic acid and of aspartic acid (probably comparable with the 

 octaspartic acid of Schiff (62)) resemble the proteins in many 

 of their properties; but these experiments also threw no light 

 upon the structure of the protein molecule beyond emphasizing 

 the already sufficiently evident probability that the amino-acid 

 grouping plays an important part in the building up of the protein 

 molecule. 



The clue which led, through a series of remarkable researches 

 to our present comparatively extensive knowledge of the groupings 

 within the protein molecule, was obtained by Curtius (9) who, 



