204 PLANT PHYSIOLOGY 



destroyed. This is a genuine masterpiece of hypothesizing, but, 

 until more enzymes are isolated, these points, like many others in 

 plant physiology, will remain unsettled. 



Accelerators. — The activity of enzymes is much influenced 

 by the addition of small quantities of an electrolyte (acid, alkalies, 

 or salts) as previously mentioned. This action when favorable is 

 said to be accelerating. It may be connected with the electrical 

 charge of the colloidal enzymes and their general properties as 

 colloids; but some ions have a very specific effect, as shown by 

 Doby and Hibbard (1927), who report that amylase is strongly 

 accelerated by Cl~ ions but only weakly by K + and NO 7. Saccha- 

 rase, on the other hand, is strongly accelerated by NO7, less by 

 K + , and is paralyzed by Cl~. A different type of accelerating 

 action, which is probably not electrolytic, is that of certain amino 

 acids such as asparagine upon amylase. 



Inhibitors or Paralyzers. — Inhibitors destroy or inhibit the 

 action of enzymes. The electrolytes mentioned above are in- 

 hibitors when harmful. Many other substances exercise an in- 

 hibitive or toxic action, e. g., mercuric chloride, hydrogen sulphide, 

 formaldehyde, hydrocyanic acid, etc. In fact much of the harmful 

 effect of these materials on the general organism may be traced to 

 their effect upon the enzymes. Of the heavy metals, mercury, 

 silver, and copper are the most toxic. 



Coenzymes. — In many cases the enzyme is accompanied by 

 some substance, the presence of which is absolutely necessary for 

 its action. This accompanying material may be separated from the 

 enzyme by dialysis and then boiled without losing its power. 

 When added to the enzyme the activity is resumed. This may be 

 repeated any number of times. Such accompanying substances 

 are called coenzymes. The separation of the bile salts from liver 

 lipase is an illustration from the animal world of the separation of 

 a coenzyme from its enzyme; while the relation of phosphates to 

 yeast zymase (Chap. XXV) and of calcium salts to pectase are 

 similar ones in the plant kingdom. 



Activators or Kinases. — In some cases the enzyme is powerless 

 when it originates and must come in contact with another sub- 

 stance which renders it active. The enzyme in this case is not 

 considered a real enzyme but a proenzyme or zymogen, while the 

 substance which renders it active is called the activator or kinase. 

 This kind of action should not be confused either with the accelera- 



