25 



as the "laccase" of alfalfa, which Euler and BoHn^ have recently 

 proved to be calcium salts of simple organic acids, then they are 

 referred to as organic catalysts. Bearing this in mind, the writer 

 will use the terms oxidizing enzyme and oxidase interchangeably 

 for convenience and with no implication that they are enzymes 

 according to the strictest definition, or that future investigation 

 may not prove the action of all the classes of oxidizing enzymes 

 to be due to the same substance or property. 



In regard to the role and the nature of many of the oxidases, 

 we are still ignorant in spite of the study that has been devoted 

 to them. In the case of enzymes like pepsin, trypsin, and lipase, 

 investigation has produced considerable advances in our knowl- 

 edge of them, but this cannot be said of the oxidases. In fact, 

 there are doubts in some cases whether certain of the oxidases 

 are enzymes at all, because a number of them have been proved 

 to be comparatively simple organic or inorganic substances. 

 How^ever, such oxidases as peroxidase and tyrosinase still hold 

 their places in the category of enzymes. In classifying the 

 oxidases several arrangements have been suggested, many of 

 which led only to confusion. After 1903, a more accurate classi- 

 fication was proposed, for it was then that Bach and Chodat^ 

 showed that the so-called oxidases of Bertrand are really com- 

 posed of three separate parts as indicated below: 



1. Oxygenase; a preformed organic peroxide resulting from 

 auto-oxidation. 



2. Peroxidase; a true enzyme which activates the oxygenase 

 or added H2O2, etc' 



3. Catalase; a substance decomposing H2O2 into H2O -f O2. 

 Since 1903, a great deal of work has been done which shows that 

 this conception of the so-called oxidases is founded on fact. 



1 Euler and Bolin. Zur Kenntniss biologische wichtiger Oxydationen : 



(a) I. (Same title as the series, Zur Kenntniss, etc.), Zts. Physiol. Chem. 57: 80. 

 1908. 



(b) II. Ueber die Reindarstellung der Medicago laccase, Zts. Physiol. Chem. 

 1: I. 1909. 



2 Bach and Chodat. Zerlegung der sogenannte Oxydasen in Oxygenasen und 

 Peroxydasen — V. Ber. Chem. Gesell. 36: 606. 1903. 



