OXIDIZING ENZYMES OR OXIDASES 115 



Then add 2 or 3 c.c. of strong caustic potash solution. 



The development of a pink colour on standing exposed to the 

 air for a time indicates the Voges-Proskauer reaction. Which of 

 the above give it ? 



3. Oxidizing Enzymes or Oxidases. When certain 

 fungi are cut open and the cut surfaces exposed to the 

 air the colourless juice or cell-sap of the plant becomes 

 blue, red, brown or otherwise colourized. A brown 

 colour also develops on the cut parts or in the expressed 

 juices of apples, pears, and many other fruits and vege- 

 table tissues. These colour changes are due to the 

 oxidation of certain compounds through the agency of 

 enzymes, which have been termed oxidases. They are very 

 widely distributed in the cells of plants and in milk and 

 other animal secretions : they are also produced by many 

 kinds of bacteria as well as by yeasts and other fungi. 



Like other enzymes, they act in a specific and restricted 

 manner upon certain definite substances only. All of them 

 behave as carriers of oxygen, yielding the latter element to 

 the substances which are oxidized, and reoxidizing them- 

 selves from the air or from other easilyreduced compounds. 

 In many cases the " browning " of plant tissues has been 

 shown to be due to reddish or brown compounds, resulting 

 from the oxidation of tannin or tyrosine by oxidases. 



Some of them, which may be spoken of as direct 

 oxidases, can utilize the free oxygen of the air ; others 

 are only able to effect oxidation in the presence of a 

 peroxide, such as peroxide of hydrogen, which readily 

 yields active nascent oxygen ; such are termed per -oxidases. 



The presence of oxidases is readily tested by means of 

 an alcoholic solution of gum guaiacum, which when 

 oxidized gives a rich blue colour. 



The addition of a direct oxidase results in a blue 



