SOME RECENT WORK ON PLANT OXIDASES 117 



colours are produced by the action of oxidases upon colourless 

 sap-soluble chromogens, the latter probably arising by the 

 hydrolysis of a complex glucoside. Much work has been done 

 by Palladin ' and his pupils in examining the distribution of 

 such chromogens, which they believe to be of fundamental 

 importance in respiration. They conceived of this process 

 as a taking in of oxygen by a readily oxidisable substance to 

 form a peroxide. The latter is then split up by oxidase, 

 yielding its oxygen for the oxidation of reducing substances 

 elaborated by the protoplasm. 



More recently Palladin 2 has brought forward the view that 

 the respiration of a substance such as glucose is a hydrolytic 

 oxidation, whereby the carbon is oxidised anaerobically to 

 carbon dioxide, and the hydrogen thus set free combines with 

 a respiratory pigment, reducing it to a colourless chromogen. 

 In the following aerobic stage oxygen is absorbed, with the 

 production of water and the pigment. These processes are 

 shown in the following equations : 



1. Anaerobic stage : 



C,H 12 6 + 6H 2 + 12R = 6C0 2 + I2RH, 



Glucose. Water. Respiratory Carbon Chromogen. 



pigment. dioxide. 



2. Aerobic stage : 



i2RH 2 + 60 2 = I2H 2 + 12R. 



An interesting example of the action of a respiratory enzyme 

 obtained from the spadix of an Aroid has lately been studied 

 by Weevers. 3 The heat-evolution in the spadix had long 

 been known, as had also the facts that it' arose from the 

 oxidation of sugars and that the products were carbon dioxide 

 and organic acids. Weevers established that oxidation could 

 be carried out actively by the enzyme in air or in an atmos- 

 phere of hydrogen. Glucose was decomposed with the forma- 

 tion of carbonic and citric acids, but without any production 

 of alcohol even when the reaction took place in hydrogen. 

 He concludes, therefore, that the enzyme cannot be a zymase, 

 for in addition to the absence of alcohol the presence of an 

 organic acid was demonstrated. 



1 Palladin, Ber. d. deut. Bot. Gesell., 1908, 26, 378, 389. 



3 Ibid. 19 1 3, 31, 80. 



s Weevers, Kon. Akad. v. Wetenschappen, Amsterdam, 191 1, Oct. 28. 



