INDUCED ENZYME FORMATION 



of the effective analogues, complete and specific reversal of the 

 inhibition was achieved by the addition of the homologous 

 amino acid. The generality of these findings was extended by 

 the independently performed experiments of Lee and Williams 

 (47) who demonstrated that the administration of ethionine to 

 the intact rat prevented the formation of tryptophan peroxidase. 

 In the experiments with the yeast (32,34,36,83), it was possible 

 to demonstrate by direct analysis that the presence of an effective 

 amino acid analogue inhibits incorporation from the free amino 

 acid pool into the protein fraction. One interesting feature 

 which emerged from these experiments is that the presence of any 

 one of the active amino acid analogues prevents the incorpora- 

 tion not only of its homologue but virtually of all the other amino 

 acids as well. Further, no peptide fragments, unique to pools 

 derived from cells incubated with an amino acid analogue, could 

 be found. 



In these studies, no evidence for an amino-acid-independent 

 transformation of a complex precursor into active enzyme was 

 obtained. The data rather led to the conclusion that the primary 

 pathway of the induced formation of enzyme in nondividing cells 

 of yeast involves the compulsory utilization of the internal free 

 amino acids. The fact that the utilization of nonhomologous 

 amino acids was blocked concurrently suggested further that the 

 first stable intermediate formed in the synthesis of an enzyme 

 molecule is of such a complexity as to demand the simultaneous 

 availability of a large portion of the component amino acids. 



THE EFFECT OF THE AVAILABILITY OF FREE AMINO ACIDS 

 ON ENZYME SYNTHESIS 



If the conclusions derived from the experiments with amino 

 acid analogues are correct, it would be expected that the ability 

 of cells to form enzyme should parallel the availability of free 

 amino acids for protein synthesis. 



One striking difference between the enzyme-forming ca- 

 pacity of yeast as distinguished from that of many Gram-negative 

 bacteria receives simple explanation in these terms. Thus, 



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