THE SYNTHESIS OF PROTEINS 7 



Borsook and Schott have found (1931) from a study of oxidation 

 potentials that the enzyme, fumarase, which catalyzes the reaction, suc- 

 cinate=fumarate, also acts as a theoretical catalyst. 



The synthesis of glycogen described by Cori and Cori (1939) is 

 another example, since in this case the reaction proceeds in either direc- 

 tion, depending upon conditions. The synthetic reaction is remarkable 

 in that a trace of the end product, glycogen, is required to start it. The 

 enzyme, phosphorylase, however, is also necessary. The reaction as a 

 whole therefore appears to be an example of autocatalysis superimposed 

 on an enzyme reaction. 



The experimental results with esters and glucosides in the presence 

 of enzymes are therefore in good agreement with theory. In the case of 

 the proteolytic enzymes, however, the results are more complicated, and 

 there is some doubt as to the occurrence of protein synthesis in the pres- 

 ence of proteinases. 



Various Possible Synthetic Reactions 



The various methods which have been suggested to account for the 

 synthesis of proteins may be roughly classified as follows : 



1. Purely catalytic synthesis, no energy added. 



a. Equilibrium point shifted in favor of protein by change 

 of concentration or other condition (plastein formation). 



b. Removal of protein as soon as formed. Insoluble proteins 

 — plastein? Synthesis of anilides (Bergmann and Fruton, 

 1941). Protein surface films (Langmuir and Schaefer, 1938). 



2. Energy added so as to shift equilibrium in favor of protein. 



a. Coupled reaction (cf. Borsook and Dubnofif, 1940, hip- 

 pur ic acid). 



b. Synthesis from building stones other than amino acids. 



Purely Catalytic Synthesis 



This mechanism (Wasteneys and Borsook, 1930) is the simplest and 

 the most thoroughly investigated. 



Theory. Proteins are hydrolyzed by enzymes and therefore they must 

 also be synthesized by the enzyme which caused hydrolysis, since 

 catalysts must accelerate the reaction equally in both directions. In order 

 actually to obtain proteins in this way, therefore, it is only necessary to 

 find conditions under which significant quantities of protein will exist 

 at equilibrium. Theoretically, more protein will exist in concentrated 

 than in dilute solution. This follows from the law of mass action which 



