CH. VIII.] OXIDASES. 231 



stituents of the cell are intimately related to oxidative 

 processes. 



Extracts of various plant tissues possess the property 

 of inducing the oxidation of certain aromatic substances, 

 either directly or after the addition of hydrogen peroxide. 

 The usual nomenclature is that an oxidase acts directly, 

 whilst a peroxidase requires the addition of hydrogen 

 peroxide. One view as to the mechanisms concerned is 

 that the complete oxidase system consists of a peroxidase 

 and an organic peroxide. The peroxidase deprives the 

 peroxide of an atom of oxygen and transfers it to the 

 substance that is oxidised (the acceptor). This view can 

 be represented as follows : 



(i.) 2 RO + 2 = 2 



Atmospheric Peroxide. 

 Oxygen. 



/O 

 (ii.) R " | + Peroxidase = RO + Peroxidase = O 



_ ^___^ 



Oxidase . A ctive 



Oxygen. 



(iii.) Peroxidase + O + A = AO + peroxidase. 



Acceptor. Oxidised 

 product. 



On this view the expressed plant juices or extracts 

 which give the direct oxidase reaction contain an organic 

 substance (RO) which can form a peroxide. When this 

 organic substance is absent, hydrogen peroxide must be 

 added to complete the oxidase system. 



The view outlined above is based on the results ob- 

 tained when the acceptor is guiaconic acid. This is present 

 in tincture of guiacum resin and is converted to guiacum 



