94 ENZYMES 



substrate that existence apart is impossible. It may be that the 

 colloidal character of enzymes is the secret of their action. At 

 any rate an artificial oxidising enzyme has been prepared by 

 mixing a suspensoid finely divided manganese, with an emulsoid 

 gum acacia. The adsorption complex so formed, if suitable 

 crystalloids were present, reacted as an artificial " laccase." 



(b) Enzymes retain their activity only over a very well-defined 

 range of temperature. It is common knowledge that physio- 

 logical processes take place most readily at body temperature. 

 Every biological laboratory is equipped with devices for keeping 

 incubators at a constant temperature say, 37-40 C. Before 

 these appliances had been perfected, investigators in this realm 

 had to keep their experimental material on their person. The 

 Abbe Spallanzani (1729-1799), in his classical work on digestion, 

 carried his digest-tubes in small pockets in his armpits for several 

 days. During the Great War, when scientific work had to be 

 carried out in all sorts of places, at least one physiologist, bereft 

 of gas regulators, had to resort to this simple but efficient method 

 of maintaining a fairly uniform temperature. In this way, 

 reactions in which they play a part differ from those usually 

 styled chemical. The rate of most chemical processes is doubled 

 or trebled when the temperature is raised 10 C. The enzymes 

 follow this rule only from 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 

 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. 12) 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 



