H. M. KALCKAR 



idea that the reproduction of a chain molecule may be accomplished 

 by the operation of mesomeric forces. According to this hypothesis, 

 the chances for reproduction are reasonable in case the new molecule 

 exists in the transitory state of a free radical (or as numerous free 

 radicals). Each unit of the daughter chain molecule existing as a free 

 radical will attempt to be picked up by the identical valence saturated 

 units of the original molecule with which they will form a mesomeric 

 three-electron bond of the type illustrated in formula IX. Delbriick 

 imagines the formation of such a chain of free radicals taking place as 

 the result of a one-step oxidation of an amino aldehyde "polypeptide" 

 chain, as in formula X (1). The peptide represents the fully oxidized 

 group, and the free radical, the partly reduced group. 



-i- -i- 



I I 



N— H H— N 



I .. .. I • 



C::0 0:0: 



I .. .. I 



Peptide Free radical 



X 



A different quantum mechanical model of autocatalysis of pro- 

 teins has been discussed in a recent review by Jordan (5). It is hardly 

 necessary to stress that such hypotheses, which are based on quantum 

 mechanical concepts, must be taken only as the very first attempt to 

 explain the type of forces which operate in phenomena like reproduc- 

 tion. As Delbriick (2) expresses it: "The point I want to make is this: 

 Quantum mechanics offers a reason why a two-step oxidation may be 

 catalyzed by a structure which is closely similar to the oxidation 

 product." 



The considerations just outlined ought to encourage us to look at 

 the problem of enzyme catalysis in terms of mesomerism. The idea 

 that a group of specific proteins called enzymes are capable of overcom- 

 ing potential barriers of 20,000 to 50,000 calories has always been 

 difficult to comprehend. It was mentioned above that the living cell, 

 in order to overcome the potential barrier which prevents the degrada- 

 tion of metabolites, had to evolve the device of catalysis. Suppose the 

 reaction A — ^ C illustrated in scheme I (page 232) were an oxidation 

 (scheme II) involving two electrons and that the intermediate B repre- 



236 



