S. SPIEGELMAN AND A. M. CAMPBELL 



complex precursor > active enzyme (1) 



complex precursor + free amino acids > active enzyme (2) 



free amino acids > enzyme (3) 



Reaction (1) assumes the preexistence in the noninduced cell of a 

 complex precursor which can be converted into active enzyme 

 without the involvement of the free amino acids. This property 

 distinguishes it from mechanisms (2) and (3) and permits an ex- 

 perimental decision. 



Evidently what we are asking is whether it is possible for the 

 precursor to become active enzyme without the participation of 

 the free amino acid pool. Putting the question this way suggests 

 immediately the necessity for examining the effect on the syn- 

 thesis of enzyme of any experimental condition which decreases 

 the availability of the free amino acids. Several methods are 

 available and have been employed for achieving a restriction of 

 this nature and they may be listed as follows : 



a. The use of amino acid analogues as specific agents to 

 prevent the incorporation of the free amino acids into protein. 



b. In the case of those cells which possess an internal amino 

 acid pool, to examine the effect of depletion and replenishment 

 of this pool under conditions which would minimally disturb 

 other components of the cell, 



c. The use of amino-acid-deficient mutants which would 

 make unavailable specific components. 



Experiments along all these lines have been realized with 

 yeast and the bacteria. The following paragraphs summarize 

 briefly the evidence obtained. 



THE EFFECT OF AMINO ACID ANALOGUES ON ENZYME SYNTHESIS 



Halvorson and Spiegelman (32) carried out a study with a 

 series of more than 40 analogues of amino acids for their effects 

 on induced formation of alpha glucosidase in Saccharomyces 

 cerevisae. A parallelism was established between the capacity of 

 an analogue to inhibit net protein synthesis, as measured by 

 growth, and its ability to suppress enzyme synthesis. In the case 



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