OXIDASES 393 



— the heating may be dispensed with, as the amount of oxidase 

 is so very small. 



The method followed by Gruess * is somewhat different. 

 The potatoes are sliced into absolute alcohol, and the oxi- 

 dases destroyed by heating to 70° for ten minutes. The 

 slices are allowed to remain twenty-four hours in absolute 

 alcohol, which should be changed at least three times. The 

 material is then superficially dried with filter paper and 

 covered with ether for a few minutes. The dehydrated slices 

 are then freed from the alcohol and ether by placing in a 

 vacuum desiccator, after which they may be ground up in a 

 mortar. Before use, i gram of the powder is ground with 

 sand and 25 c.c. of water, and then filtered. 



This method is criticized by Appleman, who points out 

 that in the process of drying, the activity of the peroxidase is 

 greatly impaired, and also that the presence of coagulable 

 proteins interferes with the stability of the peroxidase ac- 

 tivity, besides causing a low yield of enzyme. 



Identification. 



1. Guaiacum tincture in the presence of oxidase turns 

 blue provided oxygen be present. 



2. In cases where the blueing of the guaiacum tincture 

 does not take place immediately, the addition of hydrogen 

 peroxide may bring it about. 



3. Tetramethyl-/-phenylenediamine in the presence of 

 hydrogen peroxide gives a deep violet colour with an oxidase. 



4. Peroxidases set free oxygen from hydrogen peroxide 

 and other peroxides. 



For comparative experiments with peroxidase, Gruess uses 

 I gram of pulverized powder, prepared as above, which is 

 mixed and ground with sand with 25 c.c. of water. For the 

 test, 5 c.c. of the filtrate is mixed with •$ c.c. of guaiaconic 

 acid dissolved in alcohol, and "i c.c. of a -5 per cent solution 

 of hydrogen peroxide. 



Appleman, for comparative tests, allows a definite quantity 

 of the extract (see above) to act on a definite volume of 

 guaiaconic acid solution in the presence of hydrogen per- 



* Gruess; " Zeit. Pflanzenkrank.," igio, 25, 115. 



