Catalysts of Organic and Inorganic Origin. 317 



phosphate to caiTot or parsnip oxidase causes it to give a faint trace of 

 browning in one day with tannic acid which is not increased by the addition 

 of hydrogen peroxide. None of the other salts which could be made up from 

 the ash constituents (excluding iron salts) exerted any sensitising oxidase 

 action. The oxidase of the beetroot and potato appear to belong to one class 

 (betase, potatase, dahliase, russulase), those of the carrot and parsnip to 

 another, while the chief peculiarity of apple oxidase, namely, the readiness 

 with which it oxidises tannic acid, appears to be due to the presence of a 

 sensitiser such as potassium phosphate. Apple oxidase appears to have some 

 resemblance to a weak form of laccase which is also able to oxidise tannic 

 acid. 



Summary. 



Plant oxidases form a class of substances of great importance in plant 

 metabolism, but which are known merely by the reactions they cause, and 

 whose exact nature is quite unknown. 



According to Bach and Chodat they form three distinct classes of ferments 

 namely : — 



(1) Oxygenases, substances which absorb molecular oxygen forming per- 

 oxides. 



(2) Peroxidases, which increase the oxidising power of peroxides and can 

 only act in their presence. 



(3) Katalases, which destroy peroxides with an evolution of oxygen. 



It has long been known that certain of the reactions supposed to 

 characterise oxidase ferments could be produced by certain inorganic metallic 

 salts.* As the result of the detailed investigation of the oxidase action of 

 various metallic salts of copper, iron, chromium, manganese, lead, etc., upon 

 guaiacum, paraphenylenediamine, hydroquinone, pyrogallol, gallic acid, tannic 

 acid, and tyrosin, the conclusion has been formed that the correspondence 

 between the action of organic and of inorganic oxidases is extremely close. 

 It was also found that the oxidase action of a metallic salt varies according 

 to its acid combination, and that in the case of certain salts, such as sodium 

 or potassium ferrocyanide, ferricyanide, phosphate, or chromate, the oxidase 

 action was due to the acid and not to the base. In addition, oxidase action 

 may be accelerated in the presence of sensitisers such as the chlorides or 

 phosphates of sodium or potassium, or retarded or prevented by a variety of 

 amagonisers. The addition of a sensitiser may cause a "peroxidase" to act 

 in the absence of hydrogen peroxide. This applies to both organic and 

 inorganic oxidases, and determinations of the minimal amounts of metallic 



* Bertrand, 'Compt. Rend.,' vol. 122, p. 1032 (1896). 



2 A 2 



