CATALASE 69 



5 per cent solution of sodium nitroprusside and a little strong 

 ammonia, a pink colour is produced. This colour reaction, which 

 also is given by a number of other reducing substances such 

 as aldehydes, acetone, hydrogen sulphide, etc., is only given 

 by the reduced or cysteine form of the dipeptide and not by 

 the cystine or oxidized modification. The isolation of the 

 pure substance from yeast in a yield of about O'l to 0*15 

 gram per kilo has also been effected by Hopkins. 



The existence of a somewhat similar system of alterna- 

 tively oxidized and reduced materials in the plant have been 

 postulated by Palladin and termed by him respiratory pig- 

 ments ; these will be considered later. (See p. 103.) 



The existence in organic tissues and fluids of the enzyme 

 catalase, whose characteristic property is the destruction of 

 hydrogen peroxide with the evolution of oxygen, has been 

 known for some time. Wieland* recently has drawn atten- 

 tion to observations by Lesser,f Rywosch,J and Jorns that 

 anaerobes such as Bacillus tetanus and B. botulinus are deficient 

 in catalase whilst aerobic organisms such as Pneumococcus and 

 Sarcina, and facultative aerobes such as yeast contain catalase 

 in quantity. It is considered that the occurrence of catalase 

 in those cells and tissues which require oxygen is necessary 

 for the two-fold purpose of preventing the accumulation of 

 hydrogen peroxide which is toxic to the cell, and also for the 

 liberation of oxygen. Hydrogen peroxide is regarded as the 

 first product of the oxidation of hydrogen by oxygen which 

 acts as the hydrogen acceptor in the cell, 



2 + 2H = H a 2 



The catalase then acts upon the resulting hydrogen peroxide, 

 breaking it up into water and oxygen, which latter is then 

 available for further oxidation, 



H 2 o 2 = H 2 o + o 



This cycle of changes does not occur in anaerobic oxidations, 

 which may explain the absence of catalase under these con- 

 ditions. 



* Witland: " Ber. deut. chem. Gesells.," 1921, 54, [B], 2353. 



t Lesser: "Zeitch. Biol.," 1906, 48, i. 



% Rywosch : " Zentr. Bact.," 1907, 44, 295. 



Jorns: " Archiv. d. Hyg.," 1908, 67, 134. 



