OXIDASES 



395 



that normal respiration depends upon the presence of an 

 oxidizable substance, oxygenase and peroxidase. 



Peroxidases can practically always be found in living plant 

 members, but the oxygenases are less stable and are quickly 

 decomposed, giving origin to some of the respiratory carbon 

 dioxide. The amount of these enzymes varies with the stage 

 of development of the plant ; thus in the embyro, oxygenase 

 is at its minimum, but increases with the development of the 

 plant and then diminishes as the growth of the organ ceases. 



On the other hand, according to Porodko,* oxidases play 

 scarcely any part in respiration. 



The views of Bach and Chodat are not universally held ; 

 thus Moore and Whitley ,f as a result of a number of experi- 

 ments, have arrived at the conclusions that the sole difference 

 between the various plant extracts, etc., which show an 

 oxidizing action, consists in the presence of a small variable 

 amount of peroxide which is chemically unstable. Juices pos- 

 sessed of such oxidizing properties have one type of ferment, 

 a peroxidase, which acts only in the presence of peroxide, which, 

 if not present in the natural extract, must be added. There 

 is no proof of the existence of any other type of enzyme, such 

 as oxygenase, engaged in oxidation processes. Thus the 

 oxidases are brought into line with hydrolytic enzymes 

 concerned in the phenomena of digestion, etc. : — 



They further point out that any substance containing a 

 peroxide linkage will activate a peroxidase just as any type 



* Porodko : " Beih. Bot. Centrbl.," 1904, 16, i. 



t Moore and Whitley : " Biochcm. Journ.," igog, 4, 136. 



