OXIDASES 501 



« 



oxide. On the other hand, it will blue guaiacum without 

 addition of hydrogen peroxide if treated with an aqueous 

 solution of the purified catechol constituent extracted from 

 pounded potato by means of boiling alcohol, the complete 

 oxidase system being thereby restored. 



A dissentient opinion with regard to the significance of 

 phenolic substances in the oxidase mechanism is held by 

 Gallagher * who points out that plant juices, especially in the 

 absence of phenols, on exposure to air may form peroxides 

 from autoxidizable substances in the tissues, which reaction is 

 independent of enzyme action. There is no necessity, there- 

 fore, to invoke the action of an enzyme to oxidize a phen- 

 olic substrate. Gallagher isolated from the potato such an 

 autoxidizable substance which was able to blue guaiacum 

 immediately in the presence of peroxidase. This substance 

 appeared to be related to the lipins ; terpenes also can 

 combine with oxygen and so effect the oxidation of guaiacum 

 in the presence of peroxidase. These views are, however, 

 disputed by Wheldale-Onslow.f 



On the other hand, Szent-Gyorgyi J sees no necessity for 

 assuming the existence of a peroxidase ; in his opinion the 

 only requisites for the direct acting oxidase system which 

 blues guaiacum are an oxidase and a substrate containing 

 catechol or a derivative ; by the oxidase the catechol (i.) is 

 converted into orthoquinone (11.), 



^^— OH '{ ^=o 



I. II. 



a substance which he has shown to give a blue colour with 

 guaiacum without the intervention of any enzyme. The only 

 difference between a direct and an indirect acting system is, 

 according to this view, that the indirect acting system has 

 the oxidase but no catechol substrate, but has instead possibly 



* Gallagher : " Biochem. Journ.," 1923, 17, 515. 



t Wheldale-Onslow : id., 1924, 18, 1549. 



X Szent-Gyorgyi : " Biochem. Zeit.," 1925, 162, 399. 



