792 15. EFFECTS OF VARIOUS FACTORS ON INHIBITION 



(1) The inhibitor is bound to the susceptible enzyme more tightly at 

 higher temperatures, i.e., the formation of the EI complex is endothermic. 



(2) The denaturation of the susceptible enzyme by the inhibitor is 

 favored at higher temperatures, the inhibitor either denaturing the enzyme 

 or combining selectively with the denatured form. 



(3) Differential effects of temperature and the inhibitor in a multienzyme 

 system occur. For example, in a divergent metabolic chain the increase 

 in temperature may increase the fraction of the total metabolism passing 

 through an inhibitor-sensitive pathway. 



(4) A second action of the inhibitor with a high temperature coefficient 

 may lead at higher temperatures to an additional inhibition that is not 

 significant at lower temperatures. 



It may be necessary to include other mechanisms in certain cases as, 

 for example, when the active inhibitor is formed metabolically from an 

 added precursor. 



Temperature Characteristics of Biological Processes and the Effects of 



Inhibition 



It has been customary for many years to express the variation of biologi- 

 cal rates with temperature in terms of the temperature characteristic, //, 

 according to the Arrhenius formulation. It was originally assumed that the 

 temperature dependence of the rate is given by the equation: 



V = Ce-f^'RT (15-49) 



where C is a constant. The value of // may be obtained either from the rates 

 at two different temperatures or by appropriate plotting. Equation 15-49 

 may be rewritten as: 



Thus a plot of log v against 1/T should give a straight line with an inter- 

 cept of log C and a slope of — ///2.303i? (Fig. 15-13). If only two tempera- 

 tures are considered, one may write: 



— = exp -— 

 Vi R 



1 1 



(15-51) 



and the temperature characteristic is given by: 



IX = 2.303R J'^" (log V, - log V,) (15-52) 



-i 2 — -^ 1 



