THE SYNTHESIS OF PROTEINS 9 



Plastein is also formed by the action of trypsin or papain on a solu- 

 tion of insulin which has been previously digested by pepsin (Haddock 

 and Thomas, 1942). 



There seems little doubt that some synthetic reactions occur during 

 plastein formation, but whether proteins are produced is still uncertain. 

 According to FoUey (1932) no substance having a molecular weight 

 of over 1000 is formed. This result has been confirmed by Ecker ( 1947) . 



Taylor (1907 and 1909) reported the synthesis of protamine sulfate 

 from a completely digested solution of the compound. The enzyme 

 preparation was a glycerine extract of liver. The substance formed was 

 identical, or very similar, to the original protamine. 



The relation of the plastein to the original protein may be tested by 

 hydrolyzing enzyme proteins. Plastein is formed in concentrated solu- 

 tions of trypsin or pepsin which have been hydrolyzed by pepsin. The 

 plastein, however, has no enzymatic activity, nor does it have the general 

 properties of the enzyme protein from which it is derived. In these cases, 

 therefore, the plastein obtained is not related to the protein originally 

 hydrolyzed (Northrop, 1947). 



There is some experimental evidence that proteins may be formed by 

 enzymatic synthesis under the proper conditions. 



Removal of Protein From Reaction Mixture. The preceding 

 section summarizes attempts which have been made to synthesize pro- 

 teins by changing the concentration of the reaction mixture so as to 

 favor the presence of the protein. 



Protein could also be accumulated if the quantity in equilibrium with 

 the hydrolysis products could be constantly removed. This operation 

 would require energy but would result in the formation of indefinite 

 quantities of protein. 



The synthesis of anilides discovered by Bergmann and Fruton ( 1944) 

 is probably an example of this type of reaction. 



Robertson (1926) suggested that protein might be synthesized at 

 liquid interfaces since the protein is concentrated there. The experi- 

 ments of Langmuir (1939) and Gorter (1937) have shown that native 

 proteins, although soluble in bulk, form an extremely insoluble surface 

 layer at the air-water interface. If this layer were constantly removed 

 a new one would form and in this way protein would be obtained. Lang- 

 muir has suggested (Langmuir and Schaefer, 1938) that the molecules 

 already present on the surface could act to regulate the formation of 

 more identical molecules. This mechanism also predicts that the syn- 



