398 



ENZYMES 



between the various plant extracts, etc., which show an 

 oxidizing action, consists in the presence of a small variable 

 amount of peroxide which is chemically unstable. Juices pos- 

 sessed of such oxidizing properties have one type of ferment, 

 a peroxidase, which acts only in the presence of peroxide, which, 

 if not present in the natural extract, must be added. There 

 is no proof of the existence of any other type of enzyme, such 

 as oxygenase, engaged in oxidation processes. Thus the 

 oxidases are brought into line with hydrolytic enzymes 

 concerned in the phenomena of digestion, etc. : 



They further point out that any substance containing a 

 peroxide linkage will activate a peroxidase just as any type 

 of acid or alkali, which increases hydrogen or hydroxyl ion 

 concentration, will activate a hydrolytic enzyme. 



The reason why a plant extract containing oxidases will 

 no longer give the guaiacum reaction when heated to 60 is 

 that the peroxide, originally present in the juice, is destroyed, 

 but not the peroxidase. So that although the heated juice is 

 inactive, its oxidizing activity can be restored by the addition 

 of a peroxide. 



The work of Moore and Whitley is corroborated by 

 Wheldale,* who finds that the power of the direct action, but 

 not the indirect, is accompanied by the formation of a brownish 

 pigment when the part is injured or subjected to the action^of 

 chloroform vapour. This action is common in the Compositse, 

 Umbelliferae, Labiatse, Boraginaceae, and certain genera of the 

 Scrophulariaceae, Rosaceae, Leguminosae, and Ranunculaceae. 

 In the Cruciferae, Caryophyllaceae, Crassulaceae and Ericaceae 



* Wheldale; " Proc. Roy. Soc., Lond.," B., 1911, 84, 121. 



