INFLUENCE OF OTHER FACTORS ON ENZYMES 203 



by boiling in alcoholic solution, and Fermi and Pernossi that 

 enzymes are only slowly acted upon in amyl alcohol solutions. 



In the dried condition it has been shown that some enzymes 

 can be heated to as high as 160 C. without losing their activity. 



Exposure to low temperatures does not appear to have any 

 marked effect upon enzymes. 



With regard to the effect of alterations of temperature upon 

 the rapidity of action of ferments, it is found that each ferment 

 is most active at a temperature called the optimum temperature, 

 which varies in the case of each ferment, and also in the same 

 ferment with the conditions of solution, presence of neutral salts, 

 reaction, and temperature to which the solution has previously 

 been exposed. As a general rule the optimum temperature lies 

 between 35 and 45 C., but according to Roberts the action of 

 trypsin increases even up to 60 C., at which temperature it is, 

 however, rapidly destroyed. 



It is stated by Bredig that the existence of the optimum tem- 

 perature and the decrease in rapidity of reaction at higher tempera- 

 tures than the optimum is due to two opposing factors. The first 

 factor is the increase in reaction velocity which rise in temperature 

 always occasions, and the second is the destruction of a portion of 

 the enzyme which gradually occurs, more rapidly as the temperature 

 is increased, and finally outbalances the positive effect due to 

 increased temperature per se. Ernst working in Bredig's labora- 

 tory tested the rate of action of Bredig's platinsol upon water-gas, 

 and found conformably to this view that it also possessed an opti- 

 mum temperature of action, the exact position of which varied with 

 the previous history of the platinsol, the period during which it had 

 been kept at the higher temperature previously to starting the 

 reaction, etc. 



Accordingly it would appear that the optimum temperature is 

 not a peculiar characteristic of enzymes, but depends upon their 

 instability at the optimum temperature and above it. It must 

 be added, however, that in presence of their appropriate substrata, 

 some ferments are very stable at their temperature of optimum 

 activity e.g., pepsin the rate of destruction being practically 

 inappreciable, and hence it appears to the writer that although 

 Bredig's view may hold in some cases it is not a universal explana- 

 tion of the existence of an optimum temperature of action for all 

 ferments. 



