410 CHEMICAL DYNAMICS 



It will be seen that from x = 0.1 to x = 0.5 the law of direct 

 proportionality very nearly holds good; from a: = 3.0 to a; = 9.0 

 the Schiitz rule very nearly holds good, while from x = 4.0 to 

 a: = 8.0 the monomolecular formula adequately expresses the 

 relationship between x and t. 



4. The Influence of Acid and Alkali upon the Rate of Protein 

 Hydrolysis by Enzymes. — Of great importance in determining 

 the rate of hydrolysis of proteins by proteolytic enzymes is the 

 reaction (H+ or OH' concentration) of the solution in which 

 digestion is occurring. The activity of pepsin is greatly en- 

 hanced by a low degree of acidity, greater acidity hindering its 

 activity through destruction of the enzyme itself by the excess 

 of acid. The activity of trypsin, on the other hand, is very 

 markedly favored by a very slight alkahnity, excess of alkali 

 being even more destructive to trypsin than excess of acid is 

 to pepsin. An excess of acid very rapidly destroys the activity 

 of trypsin, while an alkaline medium leads to the somewhat 



less rapid destruction of pepsin. According to Taylor -— — to 



N 

 jjrTn. OH' is the optimum alkahnity for the action of trypsin 



upon protamin sulphate (129). 



The nature of the part played by the alkali and acid in protein 

 hydrolysis by enzymes is by no means clear. Since acids and 

 alkalies (H+ and OH' ions) are well-known hydrolysing agents, 

 a very natural assumption regarding their influence upon protein 

 hydrolysis by enzymes is to suppose that they play the part of 

 accessory catalysors, the catalytic action of the acid or alkali 

 being added to that of the enzyme. As regards the influence 

 of acids upon the hydrolysis of proteins by pepsin, however, 

 there are many well-known facts which speak against this view. 



The influence of acids is by no means proportional to their 

 degree of dissociation as would be expected were their influence 

 due to a catalytic action of the hydrogen ion (6) (68). On the 

 contrary, hydrochloric acid has an almost specific action upon 

 the hydrolysis of proteins by pepsin, so that many observers 

 have inclined to the belief that the real ferment is in this instance 

 a compound of pepsin with hydrochloric acid (121). Loeb (74) 

 has suggested that the part played by the acid, in accelerating 

 the hydrolysis of proteins by pepsin, is analogous to the part 



