490 SCIENCE PROGRESS 



acids formed upon the digestion of the protein food reserves. 

 Very little is known beyond the fact that asparagin seems 

 usually to be the chief amino-acid formed, accompanied by 

 certain quantities of leucin and tryrosin. These amino-acids 

 pass up the stem of the germinating seedling and seem to 

 disappear in the leaf contemporaneously with the beginning 

 of photosynthetic activity. But our knowledge of these 

 phenomena is still far too nebulous to make speculation 

 profitable regarding the part played by enzymes in this subse- 

 quent synthesis in the leaf. 



The succeeding section of this paper will therefore consist 

 simply of a critical review of certain supposed syntheses of 

 proteins with the aid of enzymes, under " in vitro " conditions. 

 The earlier and more significant stage in synthesis, the first 

 linkages of the amino-acids, unfortunately cannot be discussed 

 at all from the standpoint of enzyme catalysis, 1 owing to the 

 fact that no reversible syntheses with the ereptase group of 

 enzymes have been described. 



4. Protein Synthesis by Reversible Catalysis, from the 

 Products of Protein Hydrolysis 



The probability is that the experiments now to be described 

 provide sufficient evidence to establish the fact that the catalysis 

 of protein hydrolysis can proceed in the reverse direction, that 

 of synthesis, under the action of the same enzyme ; but owing 

 to the difficulty of identifying with chemical exactitude either 

 initial or end products, very little definite information has yet 

 been obtained of the course of such a synthetic reaction. 



The so-called " plastein " 3 formation obtained by Danilewski 

 and his co-workers is a typical example of this class of experi- 

 ment. This investigator found that by leaving concentrated 

 solutions of Witte's peptone in contact with rennet, precipitates 

 were obtained which gave characteristic protein reactions. 



Preparations of peptase introduced into peptones produced 

 the same result. This work has since been confirmed and 

 extended, other enzymes being employed, and in some cases 

 similar precipitates have been obtained from solutions initially 

 containing amino-acids and polypeptides. 



1 Lawrow, Hoppe-Seyler's Zeit. f. Physiol. Chem. 51, p. I. 



* See Euler, Trans. Pope, he. cit. p. 265, for summary of this work. 



