THE PLANT OXIDASES 219 



COMPONENT PARTS OF A COMPLETE OXIDASE. 



Before going farther a distinction must be made between 

 the terms " oxidase " and " peroxidase." Originally those 

 tissues which could catalyze oxidations of natural chro- 

 mogens, or of added ones, such as guaiacum resin, ben- 

 zidine, a-naphthol, pyrogallol, or tyrosine, were said to 

 contain an oxidase; whilst those requiring the addition of 

 a peroxide, such as hydrogen peroxide, or a spontaneously 

 oxidized essential oil, in order to effect oxidations, were 

 described as containing a peroxidase. The view that an 

 oxidase consisted of a peroxidase and a naturally occurring 

 peroxide was put forward by Kastle and Loevenhart 

 (1901), and has gained very general acceptance. Keeble 

 and Armstrong (1912, 3) record that in certain flowers the 

 organic peroxide accumulates during darkness, so that 

 apparently the tissues contain oxidase at one time and 

 peroxidase at another. It has been the author's experience 

 also that the occurrence of peroxide, in a tissue which at 

 times contains it, is extremely variable. Certain species 

 of plants never have any peroxide normally, though even 

 in some of them it is possible to induce the formation of 

 small quantities by prolonged deprivation of light. At 

 present it is usual to refer to the " direct " oxidase action, 

 or to the " indirect," according as the addition of a per- 

 oxide is not or is required to bring about oxidation. 

 Strictly speaking it would be more correct to refer to both 

 as peroxidase actions, for the essential is that a peroxide 

 is split up and oxygen deprived from it is transferred to an 

 easily oxidizable substance. 



Throughout this book the term " oxidase " will be 

 reserved as a general term, as it is undoubtedly both 

 expressive and comprehensive. When dealing, however, 

 with reactions involving laccase or tyrosinase, both of 



