THE SYNTHESIS OF PROTEINS I9 



are not in equilibrium with each other when isolated from serum, but this 

 fact by no means proves that they are not in equilibrium with each other 

 in the circulating blood. 



Moore, Shen, and Alexander (1945) have found a special protein in 

 chicken embryos which is not found in adult chicken serum. 



The various equilibria indicated by these experimental results may be 

 described in terms of the present hypothesis as follows : 



Amino Acids 



If (Energy added somewhere between amino acids and proteinogen.) 

 (Intermediate?) 



\\ (Autocatalytic reaction.) 

 Proteinogen 

 ± Enzyme Jf \\ (Autocatalytic or catalytic reaction.) 

 Protein A, Protein B, Protein C, etc. 



Since all the proteins are in equilibrium with the proteinogen they 

 are in equilibrium with each other. 



The quantity of proteinogen present at any time may be very small 

 and hence difficult to detect. 



The proteinogen is probably synthesized only in cells. The formation 

 of the usual proteins from proteinogen may occur anywhere. 



No experimental evidence for the formation of normal proteins in 

 this way is at hand. It is possible that such a reaction would be observed 

 if an organism could be completely freed from one of its normal pro- 

 teins. The re-addition of this protein to the organism should then result 

 in renewed production. 



The formation of enzymes from their precursors is exactly analogous 

 to the hypothetical reaction assumed for the formation of all normal 

 proteins, and hence one of interest in this connection. The precursors of 

 the enzymes must themselves be formed from the proteinogen mole- 

 cules, and an indication of such a reaction has been noted by Allen, Ray, 

 and Bodine (1938). 



Formation of Enzymes from Their Precursors 



Trypsin from Trypsinogen. This reaction agrees quantitatively 

 with the theory for a simple autocatalytic reaction. The velocity is af- 

 fected by acidity and temperature in the same way as is the formation of 

 chymo-trypsin from chymotrypsinogen (Kunitz and Northrop, 1935) 

 or the hydrolysis of other proteins by trypsin. At pYi 5.0 and 8°C. the 



