54 



PHYSIOLOGY OF THE FUNGI 



formed when Qio is 2, 3, and 4. It was assumed that one unit of substrate 

 was transformed per unit of time at 0°C. For a reaction with a Qio of 2 

 an increase in temperature from 28 to 30°C. causes as great an increase in 

 the amount of substrate transformed as does the increase from to 10°C. 

 A small increase in temperature in the range 25 to 35°C. has a greater 

 effect on the rate of reaction than a much greater increase in temperature 

 in the lower temperature range. 



80 



70 

 E 



O60 



C 

 QJ 



'^SO 



OJ 



E 

 _o 



£40 

 o 



a> 



I 30 



"in 



3 



o 20 

 trt 



c 

 3 



10 







10 20 30 



Temperature in degrees centjgrode 



40 



I' ;g. 9. The theoretical effect of temperature on the rate of enzymatic reactions for 

 different assumed values of Qio. 



Enzymes are inactivated by heat. The inactivation may be reversible 

 or irreversible depending upon the enzyme involved, the duration of heat- 

 ing, and other factors. The temperature at which the increased rate of 

 reaction is balanced by destruction of an isolated enzyme is the so-called 

 optimum temperature (Bayliss, 1925). 



The life processes of a fungus are mediated by a large number of en- 

 zymes, which differ in their sensitivity to heat. Fungi cease to grow or 

 reproduce at temperatures lower than that required to kill them. It may 

 be assumed that the enzymes most sensitive to heat are gradually inac- 

 tivated as the temperature increases. This situation in the li^'ing fungus 

 is different from that of an isolated system in that the enzyme is in its 

 natural surroundings and the fungus is able to synthesize or repair the 

 vital enzymes in question. At some temperature we may suppose that 

 the rate of synthesis or repair of the enzyme system is exceeded by the 

 rate of inactivation. When this temperature is reached, or exceeded, the 

 activity of these enzyme systems decrease. This decreased activity is 



