S. SPIEGELMAN AND A. M. CAMPBELL 



inducer and the apparent precision with which it specifically 

 stimulates the formation of a particular enzyme. 



Monod and Cohn (55) have recently reviewed the bulk of 

 the published information relevant to inducer function. Much of 

 this knowledge we owe primarily to the efforts of these two men 

 and their collaborators. Certain experiments are particularly 

 pregnant with interesting implications for the nature of EFS and 

 it is these which will occupy our attention. 



SPECIFICITY AND THE RELATION OF AN INDUCER TO THE 

 HOMOLOGOUS ENZYME 



There are two possible mechanisms of inducer action which 

 can be formulated with sufficient exactitude to permit their 

 experimental elimination. These have been labeled by Monod 

 and Cohn (55). 



7. The Functional Hypothesis. The synthesis of an 

 enzyme is presumed to be linked to its activity, from which 

 hypothesis one would conclude that effective inducers would 

 necessarily be substrates. 



2. The Equilibrium Hypothesis. It is assumed that 

 inducers must form complexes with enzyme synthesized as a 

 sine qua non of enzyme formation. 



A number of observations eliminated the first hypothesis. 

 Thus, Spiegelman, Reiner, and Sussman (88) demonstrated 

 that maltose can induce alpha-glucosidase at pli values that 

 preclude detectable metabolism of the maltose even by fully 

 induced cells. Analogues of natural substrates have been 

 employed for similar purposes. Thus, alpha-methyl-glucoside 

 can be shown (76,82) to be an inducer of maltase under con- 

 ditions in which utilization cannot be detected. Further, 

 Monod, Cohen-Bazire, and Cohn (54) have demonstrated 

 similarly that thio-methyl-beta-D-galactoside and melibiose, 

 neither of which is detectably metabolized by strain ML of 

 E. coli, are nevertheless inducers of beta-galactosidase. 



The second hypothesis was proposed in its simplest form 

 first by Yudkin (103) who did so in terms of a mass action hy- 

 pothesis in which combination between inducer and enzyme is 



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