318 Prof. A. J. Ewart. Comparative Study of Oxidation by 



oxidases required to produce progressive oxidation in the presence of a 

 sensitiser indicate that their action can be considered as closely akin to that 

 of any enzyme. H. E. and E. F. Armstrong* have shown in a series of 

 valuable papers, and particularly in the hydrolysis of raffinose by acids and 

 enzymes, that a close correspondence exists between the action of organic 

 and inorganic hydrolysing agents. The same appears to hold for organic or 

 inorganic oxidases. 



In general, oxidases, whether inorganic or organic, may vary from strong 

 to weak. The former will cause direct oxidation from the oxygen dissolved 

 in a watery solution. The latter will transfer oxygen from labile oxygen 

 compounds such as hydrogen peroxide, or will use dissolved oxygen in the 

 presence of sensitisers such as the chlorides or phosphates of sodium or 

 potassium. Various intermediate grades of activity are shown. There is 

 no reason for separating oxidases and peroxidases as distinct classes of 

 ferments, and peroxides do not necessarily take part in all oxidase actions, 

 although water does. The supposed separation of oxidase and peroxidase 

 by fractional precipitation with alcohol may be merely the result of 

 attenuation. 



An oxidase may be a " peroxidase " to certain oxidants or may become 

 so when attenuated. Metallic oxidases act as ferments in that a small 

 amount may produce considerable oxidation, especially in the presence of 

 sensitisers such as salt with copper sulphate, sodium phosphate with 

 potassium ferricyanide, etc., and in that the oxidase appears to act as 

 an intermediary in the chemical change. 



Hydrogen peroxide may influence oxidase action : — 



(a) By providing a supply of labile oxygen. 



(b) By converting a feeble oxidase into a strong oxidase (ferrous salt into 

 ferric, ferrocyanide into ferricyanide). 



(c) By acting as a sensitiser to the oxidant substance. 



(d) By acting as an inhibitor or antagoniser in some cases. 



Various salts may act as sensitisers (sodium and potassium chlorides, 

 bromides, and phosphates) or as inhibitors (barium chloride, sodium fluoride, 

 organic or inorganic acids), and in some cases, with increasing concentration, 

 the action of the former is reversed, while a substance which is a sensitiser 

 with one oxidant may act as a reducing agent with another (copper sulphate 

 and salt on indigo carmine). 



Strong metallic poisons will arrest the action of organic oxidases or 

 destroy them (apple, potato, carrot, parsnip) if immediate contact or rapid 



* ' Roy. Soc. Proc.,' B, vol. 82, p. 349 (1910) ; vol. 80, p. 312 (1908), etc. 



