CATALYSIS AND ENZYME ACTION 65 



which it acts. Therefore in studying the effect of the con- 

 centration of the enzyme on the rate of reaction all other 

 factors must be kept uniform. 



Let us introduce some factor <p into the law of mass action 

 to represent the amount of active enzyme in the solution. 



Thus ~ == kC x becomes A * = k'<pC x . We see that there are 

 at at 



two extreme cases. The first in which y is very small, therefore 

 the enzyme causes a slow change of concentration of x. 

 Thus C* is almost constant, and the rate of change will be 

 proportional to the amount of enzyme added. The second 

 case is that in which 9? is relatively large, whence the concentra- 

 tion of x changes rapidly. The rapid alteration in C, will 

 be the predominant factor, and the rate of reaction with 

 relatively large amounts of enzyme will be apparently in- 

 dependent of the amount of enzyme added. 



Between these two extremes we find that the rate of change 

 depends partly on the amount of enzyme and partly on the 

 concentration of the substrate. These various relations may 

 exist in the same experiment. In the early stages the rate of 

 reaction may be proportional to the amount of enzyme : as 

 the concentration of the substrate diminishes the rate of 

 reaction is dependent on both the concentration of the 

 enzyme and the substrate. Lastly, in the final stages the 

 rate of reaction may become independent of the amount of 

 enzyme added. 



Moore has worked out an equation which covers all possible 

 relations of enzyme to substrate, and also takes into account 

 the reverse reaction. 



As shown in the preceding section <p will depend on the 

 condition of the enzyme, i.e. the acidity or alkalinity of the 

 solution will produce more or less active enzyme from the 

 same amount of added enzyme. 



SPECIFIC RELATION BETWEEN ENZYME AND SUBSTRATE 



Unlike many other catalysts the enzymes show a capricious- 

 ness which is sometimes extremely surprising. Hot acid or 

 hot alkali can hydrolyse all the substances that can be 

 hydrolysed by enzymes, and the products of the reaction are 

 the simplest compounds possible. The enzymes, on the other 

 hand, act only on certain definite substances and the products 

 of the reaction are often only stages in the complete hydrolysis. 



For instance, acids hydrolyse starch, glycogen, maltose, 

 lactose, cane sugar, proteins, etc., but separate enzymes are 



