INDUCED ENZYME FORMATION 



door is thus slammed upon an extremely attractive approach for 

 tackling the question of protein formation. Those who accept 

 these conclusions obviously are faced with the necessity of find- 

 ing a new approach to the solution of the problem of protein 

 synthesis. 



Adopting a mechanism of protein synthesis which involves 

 the simultaneous availability of the constituent amino acid leads 

 one quite naturally to consider a template-type mechanism. It is 

 unnecessary here to undertake an extensive discussion of the 

 recent information (3,4,12,13,21) obtained from radioactive ex- 

 periments with intact animals and tissues which have attempted 

 to decide between template and stepwise mechanisms. In 

 general, unequal labeling of the protein has been taken as an 

 argument against the template hypothesis. 



A serious difficulty is introduced by the realization that 

 the incorporation of label compounds need not provide us with 

 information relevant solely to the question of total protein syn- 

 thesis. Exchange reactions are necessarily included in the 

 information obtained from such experiments. That a very real 

 difficulty exists is well illustrated by the recent experiments re- 

 ported by Gale and Folkes (25,26) in which a dissociation of net 

 protein synthesis from incorporation by exchange reactions has 

 been demonstrated. As had been shown with yeast (32), it was 

 found that /?-chlorophenylalanine can prevent new protein 

 synthesis in Staphylococcus aureus. In addition. Gale and Folkes 

 discovered that although the presence of this analogue effec- 

 tively prevents the incorporation of phenylalanine into the 

 protein, it has relatively little effect on the exchange incorpora- 

 tion of glutamic acid. 



The existence of such phenomena makes it difficult to inter- 

 pret with certainty the significance and uniqueness of data 

 derived solely from incorporation studies. 



On the Role of the Inducer 



One of the most dramatic features of the phenomenon of 

 enzyme induction is the requirement for the presence of the 



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