202 nutrition and metabolism 



Oxidizing Enzymes 



The most typical example of an oxidizing enzyme is the mnegar- 

 oxidase, because its chemical action is well known. Most of the oxi- 

 dases known act upon complex organic compounds, changing them to 

 colored bodies. Such an oxidase is the tyrosinase which forms a 

 black, insoluble compound in tyrosin solutions. It is produced by 

 several bacteria, especially by chromogens, and its appUcation in test- 

 ing for small quantities of tyrosin has been suggested. A number of 

 oxidases are known to act upon the leuco-bodies of certain organic dye- 

 compounds, as aloin, guaiac, phenolphthalein, and others. Hydro- 

 chinon is oxidized by the dead cells of a'few molds. Strange seems 

 the oxidation of potassium iodide to iodine by the endo-oxidase of 

 a mold. Many other oxidations are supposed to be of enzymic nature, 

 but their independence of the living cell has not been proved. 



Many higher organisms are known to contain oxidases, the best 

 studied are those of certain mushrooms which change the white mush- 

 room meat into a bluish or brownish color as soon as it is exposed to 

 the air. Oxidases are very common in most of the tissues of higher 

 animals. 



Reducing Enzymes 



Among the reductases, one enzyme stands apart from all the others, 

 that is the katalase or peroxidase which reduces the hydrogen peroxide 

 to water by Uberation of oxygen. 



H2O2 + katalase = H2O -f O. 



Katalase is one of the most commonly found enzymes; it is formed 

 by practically all plants and all animals and is contained by all but a few 

 bacteria. Among these exceptions is the Strept. lacticus. The ab- 

 sence of katalase in this species has been recommended as a diagnos- 

 tic test. It is possible that this enzyme is necessary for intra-cellular 

 oxidations. 



A number of other reductases are known. Nearly all of the re- 

 ductions mentioned in the paragraph on the products of mineral 

 decomposition are proved to be of enzymic nature; these processes 

 will take place after the cell is killed by a disinfectant or is ground to 

 pieces. This can be readUy demonstrated by lacerating the cells 



