170 LAWRENCE R. PROUTY AND JAMES D. HARDY 



sion of sucrose by acids or iiivertase, conversion of fat to soap by al- 

 kali, and many oxidative reactions. 



Many physiological processes involve several complex chemical 

 reactions and the determination of the dominant reaction is the chief 

 application of the temperature characteristic. The usual procedure 

 is to study the reaction in a bath, the temperature of which is either 

 constant or variable at a controlled rate. 



Theory of the Master Reaction 



Crozier (34,35) proposed that, in a complicated physiological reac- 

 tion such as cellular oxidation, there may be a slowest step which 

 governs the over-all velocity of the process. He further suggested 

 that in this type of reaction, the temperature coefficient of the reac- 

 tion velocity (Qw) yielded a quantity similar to energy of activation. 

 This quantity (the temperature characteristic or n) changed in value 

 on passing from one temperature range to another and these changes 

 were interpreted as shifts in "mastery" from a reaction with a velocity 

 constant ki(ni) to a reaction with a velocity constant kiini). Crozier 

 believed that Ai and A'2 were constants for the rates of formation and 

 destruction of an enzyme. By dominating the steady state concen- 

 tration of an enzyme, these constants also regulated the over-all 

 velocity of the reaction. Many enzymes are common to many dif- 

 ferent biological species and different life processes. Thus, it might 

 be predicted that a random distribution of temperature characteristics 

 for many diverse physiological reactions in different species would not 

 exist. Rather, well defined modes corresponding to either ki or k2 

 for various enzymes would be expected. Crozier's plot of fx values 

 against frequency of their occurrence shows these modes. 



The rate of the heart beat might be determined, for example, by a 

 single type of activation because of the interdependence of the several 

 reactions involved (35). In any such related chain of reactions, it 

 would be the slowest reaction that would determine the rate for the 

 entire process and act as the "master reaction." The chain of reac- 

 tions associated with muscular contraction, flavoprotein systems, and 

 cytochrome, are also examples. In these cases in which the Arrhe- 

 nius plot does not give a straight line, Crozier calls the point of slope 

 change the critical temperature at which dominancy changes from 

 one master reaction to another. 



Considerable experimental evidence has been collected by Crozier 



