FACTORS INFLUENCING ENZYME ACTION ll'j 



follow this rule only from 0° C. to a temperature called their 

 optimum temperature, above which the rate decreases rapidly. 

 The optimum temperature of most enzymes lies between 30° and 

 40° C. The decrease in rate of reaction when the temperature 

 is allowed to go over 40° C, is probably due to coagulation of the 

 enzyme. Increase in temperature causes alterations in the physical 

 state of colloidal matter. These alterations, in viscosity, in 

 colour, and in conductivity, all indicate an increase in the size 

 of the colloidal particles, and consequently a decrease in their 

 specific surface. The effective adsorbing surface is diminished. 

 At the optimum temperature the increased chemical action due 



TEMPER.ATUR.E 



Flti. 27.— Graph to show liow the effect of increase of temperature on tlie rate of enzyme 

 action is the result of the interaction of two factors, (1) increased chemical action and (2) 

 increased destruction of enzyme. 



to temperature more than balances the decreased adsorbing 

 surface. Beyond this temperature, the loss of surface becomes 

 relatively important. If the temperature is raised till the specific 

 surface is reduced, by coagulation, to a value below 10,000, 

 adsorbing power is totally lost, chemical action is stopped, and 

 the enzyme is said to be dead. 



In the appended figure (Fig. 27) curve 1 (dotted line) shows 

 how, as the temperature increases, a pure chemical action is 

 accelerated. Curve 2 (dash line) represents the rate at which the 

 effective surface is decreased by rising temperature. The process, 

 it will be noticed, is not an instantaneous one, but proceeds with 

 a definite velocity which increases very markedly somewhere 

 about 30° C. Curve 3 (firm line) is the graph of the rate of the 

 same chemical reaction as shown in (1), but carried out by enzyme 



