INDUCED ENZYME FORMATION 



by the work of Vogel and Davis (99) withA^-acetyl-ornithine 

 deacetylase and by Stanier's (91) and Suda's (92) skillful use of 

 sequential induction. 



It will be noted that comparatively irreversible combina- 

 tions of inducer are assumed to occur only when both template 

 and a replica are present. This situation possesses interesting 

 predictive consequences which are sufficiently unique to permit 

 experimental examination. It is evident immediately that the 

 state of a noninduced cell, with the majority of its templates 

 unoccupied by enzyme, should be very different from one which 

 is induced to the condition where a considerable portion of the 

 templates are already in the active state, and where enzyme mole- 

 cules are freely available for the formation of new active com- 

 plexes. 



In the first place, differences in response to inducer concen- 

 tration in noninduced as compared with partially induced cells 

 would not be unexpected. Induced cells would contain the 

 T-E complexes permitting the relatively irreversible combination 

 with inducer molecules. This is of course most dramatically 

 exhibited by the long-term adapting instance. Here, no level 

 of inducer concentration is capable of stimulating enzyme for- 

 mation in the vast majority of cells. However, once this is suc- 

 cessful and an induced cell is produced, normal inducer levels 

 are sufficient to maintain enzyme formation indefinitely. An 

 analogous difference can also actually be seen in normal enzyme 

 formation. Thus, with alpha-methyl-glucoside as an inducer it 

 is found that the concentration levels required to initiate induc- 

 tion are considerably higher than those needed to maintain 

 enzyme formation once it is started (77). The same observa- 

 tion has been made independently by Monod (cited in ref. 15) 

 and Spiegelman and Gilmour (81) with respect to beta-galac- 

 tosidase synthesis in E. coli. Here enzyme formation does not 

 commence at thio-methyl-D-galactoside levels of 1 X 10~^ A/ 

 but will if the concentration is raised to 5 X 10~^ M. However, 

 once enzyme formation is begun, 1 X 10~^ M is perfectly ade- 

 quate to maintain the induction. 



147 



