S. SPIEGELMAN AND A. M. CAMPBELL 



with a view to seeing whether it circumscribes the nature of the 

 induction mechanism sufficiently to serve as a useful guide in the 

 construction of a more suitable model. 



THE KINETICS OF ENZYME SYNTHESIS 

 AND ITS INTERPRETATION 



One of the most obvious ways of examining the adequacy of 

 mechanisms analogous to the activator hypothesis is in terms of 

 its kinetic consequences, and historically this was the first type of 

 data provided. The kinetics found for the induced synthesis of 

 maltase and galactozymase in yeast were found to be auto- 

 catalytic and could be accurately described by the logistic equa- 

 tion (71,72). Subsequently other systems were found to obey 

 the same kinetics (41). 



The results obtained suggested that in the early phases of 

 the induction, enzyme-forming capacity increases as new enzyme 

 molecules are produced. The data are clearly inconsistent with 

 a simple activator hypothesis, and on the same ground the Yud- 

 kin mass action model (103) for inducer function was rejected 

 (71), since it also predicts maximal rates of enzyme formation 

 from the onset of induction. To explain the autocatalytic 

 kinetics, as well as certain data of a genetic nature to which we 

 will have reference below, the so-called "plasmagene" hypoth- 

 esis was proposed (72). In this it was assumed that the in- 

 ducer functions by stabilizing a complex between enzyme and 

 the "plasmagene" and that this complex is capable of replicat- 

 ing itself and producing enzyme. The widespread implica- 

 tions of this hypothesis and the admittedly limited experimental 

 support available at its formulation acted as a stimulatory 

 irritant. Equally plausible alternatives for explaining the 

 logistic kinetics were quickly offered by a number of authors. 



Thus, it has been argued (53) that enzyme formation was 

 being followed in these studies employing metabolizable inducers 

 which could serve as an energy source. Under such circum- 

 stances, obviously the more enzyme there is present, the greater 

 is the rate of energy generation, and the more rapid therefore 



132 



