76 ENZYMES 



side the body are oxidized with difficulty, are completely oxi- 

 dized to carbon dioxide and water within the cells, and that this 

 is done with just such a degree of rapidity that the heat pro- 

 duced is in exactly the amount necessary for the wants of the 

 body. l There can be little question that this oxidation is 

 accomplished through catalytic agents acting within the cells, 

 and certain of them have been placed in a condition permitting 

 of study. As yet their exact relations to intracellular oxidation 

 are not clearly defined, but for the present they may be grouped 

 provisionally as oxidizing enzymes. One of the most studied 

 of these is 



Catalase. It has long been known that most enzymes pos- 

 sess the power of decomposing hydrogen peroxide, with libera- 

 tion of oxygen; but it was not until 1901 that it was finally 

 demonstrated by Loew 2 that this property was due to a separate 

 enzyme and was independent of the specific properties of the 

 various other enzymes. s This ferment is very wide-spread, and 

 so is generally obtained along with the other enzymes when 

 attempts are made to isolate them from the cell. It was named 

 catalase by Loew, and he described two forms, a-catalase, which 

 seems to be a nucleoproteid, and fi-catalase, which has the 

 properties of an albumose. It has been demonstrated by Bach 

 and Chodat 4 that peroxides are contained in plant cells, and 

 from the wide distribution of catalase it seems probable that 

 they also occur in animal cells. Just what function the catalase 

 performs is at present merely a matter of speculation. Loew 

 considers that it destroys peroxides formed in metabolism, which 

 are very poisonous to cell life. Shaffer 5 has found evidence 

 that under the influence of catalase the oxygen liberated is in 

 the molecular form, O 2 , and therefore relatively inert ; whereas 

 when peroxides spontaneously decompose, they liberate atomic 

 oxygen which is an active oxidizing agent. He found that uric 

 acid is oxidized by peroxide of hydrogen, but when catalase is 

 present, this oxidation is prevented. According to this the func- 

 tion of catalase is rather to prevent dangerous forms of oxida- 

 tion than to help in normal oxidative processes. For the 

 present, however, nothing can be said positively on this 

 subject. 



1 A full discussion of this subject is given by Hammarsten, " Physiological 

 Chemistry, " introductory chapter. 



2 Keport No. 68, U. S/Dept. of Agriculture. 



3 Other observers had previously suggested the same possibility, and Jacob- 

 son had proved the independence of catalase action. 



4 Berichte der chem. Gesellsch., Vols. 35 and 36 : several articles. 



5 Amer. Jour, of Physiol., 1905 (14), 300. 



