EFFECTS OF TEMPERATURE: CELLULAR SYSTEMS 



793 



The plotting procedure is preferred because linearity cannot always be 

 assumed. If a curve is obtained, the // at any temperature can be calculated 

 from the slpoe at that point. When T^ — T^ = 10°, v^jv-^ is Q-^q and thus 

 the relationship between // and Q^^ for temperatures in the neighborhood 

 of 30O may be written as: 



1.1 = 42,200 log Q,o 

 It mav be noted that u is usually given in small calories. 



(15-53) 



Fig. 1.5-13. Plot of log v against l/T for the determination of 

 the temperature characteristic [x (Eq. 15-50). 



It is possible to obtain // values from systems of any degree of complexity 

 and they serve to characterize the temperature dependence of the rates. 

 However, the physical interpretation of // becomes more and more difficult 

 as the complexity of the system increases. The principle of limiting reactions 

 has often been called uiDon to interpret // values obtained from cellular 

 systems and it is claimed that // relates only to the single limiting reaction 

 that controls the over-all rate. This has given rise to much argument, 

 which is beyond the scope of this book, but reference may be made to Chap- 

 ter 7 in which reasons were given for believing that the metabolic or func- 

 tional rates in living systems are generally not determined by single reac- 

 tions. Indeed, it is well to consider what // means for a single enzyme reac- 

 tion. It has been frequently stated that // is the activation energy for the 



