266 ORIGIN OF STRUCTURES AND FUNCTIONS 



The very interesting experimental results obtained by 

 R. B. Khesin^^^ show that isolated secretory granules of the 

 pancreas cannot make direct use of the energy of ATP for 

 the synthesis of the protein-enzyme amylase. In them the 

 synthesis of the enzyme from free amino acids only occurs 

 as a result of the activity of substances which are elaborated 

 independently by other formed elements in the protoplasm, 

 the mitochondria, in the course of their energy-exchange 

 reactions which take place in the presence of ATP under 

 aerobic conditions. The actual synthesis of protein by the 

 granules can, however, proceed in the absence of oxygen. 



The part played by enzymes in the processes supplying the 

 energy required for synthesis is now ^vorked out in great 

 detail but the position is far worse in regard to the part 

 played by enzymic systems directly in the biosynthesis of 

 proteins. 



As early as 1886 A. Danilevskii"^ first indicated that syn- 

 thetic reactions might be brought about with the help of 

 proteolytic enzymes. On digesting dilute solutions of different 

 proteins with pepsin and then concentrating the peptones 

 thus obtained and allowing fresh portions of pepsin to act on 

 them, Danilevskii observed the formation of an insoluble 

 precipitate, which he believed to be protein ^vhich had 

 arisen as a result of the enzymic synthesis. Furthermore, it 

 was established that these precipitates, which were called 

 ' plasteins ', could be obtained from peptic hydrolysates of 

 a very large number of proteins by enzymic synthesis because, 

 owing to the removal of the insokible products of the reaction 

 by precipitation, the equilibrium was displaced away from 

 hydrolysis and towards the synthesis of peptide bonds. ^^® The 

 plasteins have since been studied in detail by all modern 

 methods."^ They seem to be polypeptides, with molecular 

 weights of some thousands, containing a predominance of 

 hydrophobic amino acids and apparently lacking any specific 

 biological properties."* 



Comparatively recently H. Tauber"' has succeeded in 

 bringing about the enzymic synthesis of proteins by the 

 action of chymotrypsin on a mixture of peptides. Chymo- 

 trypsin also catalyses the formation of peptides from esters 

 of amino acids, in which reaction the energy needed for the 



