HISTOLOGY AND CHEMISTRY OF FUNGI 57 



as a thermolabile catalyst in solution. In connection with this defini- 

 tion, it is important to know that a catalytic agent is one which alters 

 the rate of a reaction without itself entering into the final product 

 (Ostwald, 1902), or which does not appear to take any immediate part 

 in the reaction, remains unaltered at the end of the reaction and can 

 be recovered again from the reaction product unaltered in quantity 

 md quality. 



Enzymes differ from ordinary inorganic catalysts in their sensitive- 

 less to heat and light. They are destroyed at 100° C, and most of 

 -hem cannot be heated safely above 60° C The velocity of the 

 •eaction increases with a rise of temperature up to an optimum and 

 IS the temperature is increased above the optimum the enzyme is 

 jermanently inactivated. Enzymes retain activity even after ex- 

 )osure to action of liquid air. Light in its ordinary form in the pres- 

 tnce of oxygen and ultraviolet light independent of oxygen are de- 

 tructive to enzymes. Again, enzymes possess most of the important 

 )roperties of colloidal solutions, such as their non-diffusibility. They 

 .re soluble in water, in dilute salt solutions, or in glycerin. They 

 xhibit the phenomenon of adsorption. 



An important discovery has recently been made which has thrown 

 onsiderable light on the activity of enzymes, and that has been the 

 timulation exercised by certain substances which have been called 

 ctivators and the inhibition exercised by other substances, which have 

 een called paralyzers. The activators are in some cases simple chem- 

 :al substances, such as acids, alkalis and salts, or they are complex 

 odies of unknown chemic character, but they have this in common that 

 ley can be separated from the enzyme by dialysis, and are not de- 

 coyed by heating. An enzyme may be rendered inactive by the 

 ;moval of its activator, but it can be restored to activity by mixing 

 |ain with this substance. In the case of some enzymes, the inactive 

 ibstance, as it is formed in a cell may be called a zymogen, or prof or- 

 ient, but when associated with the activator the active enzyme is 

 jveloped. An activator is inorganic. A kinase is a more or less 

 )mplex organic body which activates a proferment. 



Substances which reduce, or destroy, the activity of enzymes are 

 -lied paralyzers, which may be formed as products of enzymatic 



' Haas, Paul, and Hill, T. G. : An Introduction to the Chemistry of Plant 

 roducts. 1913: 340-341. 



