FACTORS INFLUENCING ENZYME ACTION 95 



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 

 action. fc This curve may be drawn by plotting the differences of 

 the ordinates of (1) and (2) on the same scale of temperatures. 



(c) The hydrogen ion concentration of the medium in which 

 the enzyme acts has much to do with its activity. Each enzyme 

 is active only when the bathing fluid has a p H of a certain range 

 with an optimum p a at which the action proceeds at its best. 



TEMPER.ATUFLE: 



FIG. 12. Graph to show how the effect of increase of temperature on the rate of 

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

 action and (2) increased destruction of enzyme. 



The extraordinary sensitiveness of colloids to the p u has been 

 mentioned. 



(d) The crystalloid content of the substrate solution is peculiar 

 for each enzyme. Certain salts are, of course, destructive. All 

 salts which break up colloidal complexes, inhibit or destroy 

 enzyme action. Enzymes are " salted out " by the neutral salts 

 that precipitate colloids and may thus be separated. 



(e) Anaesthetics have no effect on enzyme action. 

 Chloroform, thymol, etc., may therefore be used to keep experi- 

 mental enzyme solutions free from bacteria. 



To sum up, the ranges of temperature, p H , salt content, etc., 

 all point to the colloidal nature of enzymes. 



The material on which an enzyme acts is called its substrate, 

 and each enzyme acts on a specific substrate and on no other. In 



