S. SPIEGELMAN AND A. M. CAMPBELL 



competitive inhibitor of the beta-galactosidase, was nevertheless 

 incapable of inducing the formation of this enzyme. Other 

 specific complexants, e.g., neolactose and phenyl-beta-D- 

 galactoside, were similarly found devoid of inductive capacity. 



An instance of an apparent violation of the third deduction 

 was provided by Spiegelman and Halvorson (82). The dis- 

 sociation constant of methyl-alpha-D-glucoside, an inducer of 

 alpha-glucosidase synthesis in Saccharomyces cerevisiae, was deter- 

 mined and compared with the constant derived from its com- 

 plexant properties with enzyme. The two values were found to 

 differ by a factor of about two hundred. 



It must be emphasized that the types of hypothesis made 

 unlikely by the experiments cited are highly restricted in nature. 

 All of these experiments had in common an examination of the 

 effect of the inducers as enzyme complexants in terms of meas- 

 urable effects on enzymatic function. By their very nature 

 they could not preclude the possibility of combination at some 

 site which possessed no consequences in terms of a detectable 

 modification of enzyme activity. 



It must further be noted that such experiments do not 

 eliminate the possibility that inducer serves as a coupling agent 

 which leads to the formation of a stable complex among enzyme, 

 inducer, and a third component. If the inducer would combine 

 with enzyme effectively only in the presence of the third com- 

 ponent, violation of all three predictions could obtain. 



THE QUESTION OF STOICHIOMETRY OF INDUCER ACTION 



Until the advent of the resourceful exploitation by Pollock 

 of the penicillinase-forming system of B. cereus, the question of 

 stoichiometry was one which could be formulated but hardly 

 resolved. Pollock (59-61) discovered that fleeting exposures of 

 cells to minute concentrations of penicillin at ° C. can lead to 

 the specific adsorption of enough inducer molecules to permit 

 penicillinase formation even subsequent to the destruction of all 

 unbound penicillin. With the use of S^^-labeled penicillin it 

 was found that specific fixation is saturated at about 80 atoms 



130 



