142 NUTRITION AND METABOLISM. 



the protein into bodies which diffuse easily into the cell. Here, proteoly- 

 tic endo-enzymes further decompose these products. Such an endo- 

 enzyme is the amidase discovered by Shibata in the mycelium of Aspergil- 

 lus niger which forms ammonia from urea, acetamid, oxamid, biuret. 

 Endo-erepsin and amidase were also found in Penicillium camemberti by 

 Box. 



Similar to these proteolytic enzymes is the urease which is formed in 

 large quantities in the so-called urea bacteria, but it is also present in the 

 mycelium of some molds. An endo-enzyme, splitting hippuric acid into 

 benzoic acid and glycocoll, is found in the mycelium of a few molds. 



OXIDIZING ENZYMES. 



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

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

 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 application in testing 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. Hydrochinon 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 liberation of oxygen. 



H 2 O 2 + katalase =H 2 O+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 



