2 TRANSACTIONS OF SECTION K. 577 
2. On Oxidase Enzymes. 
By Professor Aurrep J. Ewarr, D.Sc., Ph.D. 
Plant oxidases form a class of substances of great importance in plant meta- 
bolism. They are known merely by the reactions they cause, and their exact 
chemical nature is quite uncertain. According to Bach and Chodat they form 
three distinct classes of ferments, namely :— 
(1) Oxygenases, proteins which absorb molecular oxygen forming peroxides. 
(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, &c., upon guaiacum, para- 
phenylendiamin, 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 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 
may be retarded or prevented by a variety of anti-oxidases. This applies to 
both organic and inorganic oxidases, and determinations of the minimal 
amounts of metallic 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 an enzyme. 
In general, oxidases, whether inorganic or organic, may vary from strong to 
weak. The strong will cause direct oxidation from the oxygen dissolved in a 
watery solution. The weak will transfer oxygen from labile oxygen com- 
pounds 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. The oxidase action of a 
metallic salt varies according to its acid combination, and metals such as iron or 
chromium may give salts an oxidase action when the metal is present as base or 
as acid (potassium ferricyanide, bichromate, &c.). 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. The supposed separation 
of oxidase and peroxidase by fractional precipitation with alcohol may be 
merely the result of attenuation. Metallic oxidases act as ferments in that a 
small amount may produce considerable oxidation, especially in the presence of 
sensitisers (copper sulphate and salt, potassium ferricyanide and sodium phos- 
phate), and that the oxidase appears to act as an intermediary in the chemical 
change. Nitric acid and potassium permanganate, on the other hand, transfer 
oxygen in the first instance from themselves. 
Hydrogen peroxide may influence oxidase action (a) by providing a supply 
of labile oxygen; (b) by converting a feeble oxidase into a strong oxidase (fer- 
rous salt into ferric, ferrocyanide into ferricyanide) ; (c) by acting as a sensitiser 
to the oxidant substance ; (¢) by acting as an anti-oxidase in some cases. Various 
salts may act as sensitisers (sodium and potassium chlorides, bromides, and 
phosphates) or as anti-oxidases (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 an anti-oxidase with another. This applies also to the peroxide of 
hydrogen, and, in the presence of an excess of this substance, an oxidase may 
act as a reducing agent (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 penetration is 
assured. Hence the organic oxidases are possibly proteids with or without 
oxidase metals in basic or acid combination. 
There is no justification for the use of such terms as ‘peroxidase,’ ‘kata- 
lase,’ ‘cenoxydase, or ‘ tyrosinase ’ to indicate specific substances, ferments, or 
1914. ote 
