Catalysts of Organic and Inorganic Origin. 291 



(1) Oxygenases, proteins 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. 



An oxidase which turns guaiacum blue without hydrogen peroxide being 

 added is a mixture of ferments of the first and second class. Thus Bach* 

 •considers tyrosinase to be a mixture of a specific oxidase and a specific 

 peroxidase. 



Moore and Whitleyf conclude that all oxidases are peroxidases acting in 

 the presence of a peroxide, such as may be present in certain solutions of 

 guaiacum, or an organic peroxide derived from the juice of the plant tested. 

 The peroxides can be removed from the juices and from guaiacum by adding 

 animal charcoal and filtering, and they are destroyed by heating to 

 55°-60° C. for several hours. After such treatment potato juice will only 

 give a blue with guaiacum on adding H 2 2 . 



As a matter of fact the action is merely to attenuate the oxidase, so that 

 the addition of an accelerator such as H2O2 is necessary to render the 

 oxidation of the guaiacum perceptible. The facts that potato juice decom- 

 poses peroxides strongly, and that the juice and pulp give negative results 

 when tested with decolorised magenta, and show no effervescence until H2O2 

 is added, are hardly in accord with Moore and Whitley's explanation, and a 

 study of the preceding Tables shows that, so far as metallic oxidases are 

 concerned, too much importance can easily be attached to the influence of 

 peroxide of hydrogen on oxidase action. Thus in some cases the same 

 substance may be a katalase, an oxidase, and a peroxidase. In other cases 

 the same metallic salt may be an oxidase to one reagent, a peroxidase to 

 another, ineffective to another, and may or may not at the same time be a 

 katalase. Finally, the mere addition of H 2 2 may convert a weak oxidase 

 ■(" peroxidase ") into a stronger one, which will then act in the absence of 

 H 2 2 (ferrous salts and potassium ferrocyanicle). 



Moore and Whitley found that hydrochloric acid of 1/800 normal concen- 

 tration nearly destroyed potato oxidase, and quite destroyed carrot oxidase, 

 while sodium hydrate of similar concentration had no effect. On the other 

 hand, Na 2 HP0 4 had a stronger destructive action than NaH 2 P04. The 

 reaction may, however, be prevented without the oxidase being destroyed. 

 Thus the addition of hydrochloric acid (or sulphuric) to ferric chloride 

 removes its power of giving a blue with guaiacum, while tartaric and citric 



* ' Berichte,' vol. 39, No. 10, p. 2126 (1906). 

 t ' Biochem. Journ.,' vol. 4, p. 136 (1909). 



