CHEMICAL COMPOSITION OF PLANTS 67 



the influence of different admixtures, of which it is most difficult 

 to purify the enzyme solutions, as well as in dependence upon 

 the colloidal nature of the substances associated with the enzyme. 

 Of great physiological significance is the change of the activity 

 of enzymes under the influence of various kinds of ''activators" 

 and ''paralyzers." These designations are given to substances 

 that, being added sometimes in the slightest quantities, exert a 

 great influence upon the work of enzymes. An especially 

 thorough study has been made of the activators of proteolytic 

 enzymes, and it has been proved that different groups of pro- 

 teases are activated by different substances. Thus, enzymes of 

 the group of papain are activated by hydrocyanic acid and 

 hydrogen sulfide, in particular by natural compounds including 

 the sulphydryl group SH, the most important of which are 

 glutathione and cysteine, that are liberated in the process of 

 hydrolysis of protein substances. Tryptases are activated by a 

 special activator enterokinase, first demonstrated by Pavlov. 

 It is secreted by the mucous membrane of the intestine, but its 

 nature has not yet been ascertained. HCN, H2S, and glu- 

 tathione do not activate tryptase ; on the contrary, they suppress 

 its action. For the group of peptases, no activators are as yet 

 known. 



Closely allied to the activators are the so-called ''coenzymes," 

 the presence of which is thought by some authors to be quite 

 indispensable for certain enzymatic reactions. The action of the 

 coenzyme is very often represented in the following manner: 

 the coenzyme reacts with the initial substance, and this complex 

 is then subject to the action of the enzyme. The enzyme is 

 not capable of acting upon th'e initial substance when in its pure 

 form but only after it has become combined with the coenzyme. 

 Antienzymes, on the contrary, inhibit the activity of enzymes, 

 transforming the initial substances into compounds that are 

 unavailable to the enzyme. About the action of coenzymes and 

 antienzymes, however, very little has thus far been ascer- 

 tained, and the distinctions between them and activators and 

 paralyzers is not yet established. Some authors, as, for instance, 

 Kostytchev, completely deny the existence of coenzymes and 

 antienzymes. 



A very characteristic peculiarity of enzymes is the specificity 

 of their action. It has been shown that starch is converted into 



