EFFECTS OF TEMPERATURE: ENZYMES 



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The most complete studies of the variation of enzyme inhibition with 

 temperature are those of Gressly and Aebi (1959; Gressly et al., 1959). 

 The actions of azide, hydroxylamine. 2.4-dichlorophenol, and 3-amino-l,2-4: 

 triazole on mouse liver catalase were determined at different concentrations 

 and temperatures. Typical concentration-inhibition curves for azide are 

 shown in Fig. 15-3 and the marked shift with temperature is evident. In 



Fig. 15-3. Inhibition of catalase by azide at three different 

 temperatures. (From Gressly et al., 1959.) 



Fig. 15-4 the effects of temperature on all the inhibitions are summarized. 

 It is interesting that although three inhibitors follow the usual exothermic 

 pattern, the inhibition by 3-amino-l,2,4-triazole is endothermic. The en- 

 thalpy change for azide inhibition is quite high: ]H = — 14.6 kcal/mole, 

 JjF = — 7.6 kcal/mole, and J*S = — 22.6 cal; mole/degree. Another in- 

 hibition that increases with rising temperature is that of 1,10-phenanthro- 

 line on succinic dehydrogenase, preliminary experiments at the 1 mM 

 level showing 13% inhibition at 17°, 14.5% inhibition at 27°, and 17.2% 

 inhibition at 37° (Sanyal, 1959). 



Perhaps the most endothermic inhibition yet reported is that of 500 mM 

 urethane on yeast /?-fructofuranosidase between 45° and 65°, in which range 

 the inhibition increases from 28% to 97% (Johnson et al., 1948). It is likely 



