THE CHEMICAL PROCESSES IN PLANT RESPIRATION II3 



The following substances were described as oxidising enzymes 

 or the so-called oxidases by older writers: 



Laccase, obtained from the Japanese lacquer tree by Yoshida 

 and G. Bertrand/ was the first known oxidase. Then it was 

 discovered in various rubber trees^ and to-day is admitted to 

 be a widespread enzyme. Yet in some cases laccase proves to 

 be a mixture of peroxidase and organic peroxides. In other 

 cases it can be identified only by means of various color reactions 

 as e.g. by the blue coloration of guaiacum, etc' From the 

 preceding statement it is evident that all these color reactions 

 are hardly reliable because the presence of autoxidators can 

 be proven only by gasometric determinations of the absorption 

 of oxygen from the surrounding air. The color reactions are 

 in many cases due to the transfer of atomic oxygen and so have 

 nothing to do with the activation of molecular oxygen. 



Tyrosinase, which oxidises tyrosin to brown pigments, was 

 discovered by Bourquelot and Bertrand^ and seems to represent 

 a specific activator of oxygen. According to Bach and Chodat^ 

 tyrosinase always consists of the usual components — oxygenase 

 and peroxidase. 



Oenoxidase was discovered in fleshy fruits'^ and likewise appears 

 to represent a non-uniform substance. Hence we are well 

 entitled to conclude that the existence of specific oxidising 

 enzymes in the sense of catalysts is by no means proven, as 

 Engler and Herzog also point out. 



O. Warburg*^ has proposed a noteworthy physical-chemical 

 theory of cell respiration which is provisionally supported only 

 by experiments with animal cells and inorganic models, and 



1 Yoshida. Jour. Amer. Chem. Soc. 43: 472. 1883; Bertrand, G. Compt. rend. 118: 

 1215. 1894: 120: 266. 1895; 121: 166. 1895; 122: 1132. 1896; 14s: 340. 1907; Bull, 

 de la soc. de chim.-biol. (IV) i : 1120. 1907. 



^Spence, D. Biochem. Jour. 3: 165, 35r. 1908; Cayla. V. Bull, de la soc. de chim.- 

 biol. 65: 128. 1908; and others. 



5 Bourquelot, E. et G. Bertrand. Jour, de pharni. et de chim. (VI) 3 : I77. 1896; Bull, 

 de la soc. mycol. 1896: 18, 27; 1897: 65; Gessard. Compt. rend, des seances de la soc. de 

 biol. (X) 5: 1033. 1898; Bertrand, G. Compt. rend. 122 : 1215. 1896; 123 : 463. 1896; 

 Bertrand, G. et Mutermilch. Ibid. 144: 1285. 1907; Ann. de I'inst. Pasteur. 21: 833- 

 1907; Zerban, F. W. Jour. ind. eng. chem. 10: 814. 1918. 



< Bach, A. Ber.d. chem. Ges. 39:2126. 1906; Chodat et Staub. Arch, de sci. physiques 

 et nat. Geneve' (IV) 23: 265. 1907; and others. 



sLaborde. Compt. rend. 126: 536. 1898; Cazeneuve. Ibid. 124: 406, 751. 1907; 

 Bouffard. Ibid. 124: 706. 1907. 



6 Warburg, O. Biochem. Z. 119 : 134- 1921 ; 136: 266. 1923; 142 : 5i8. 1923; Zeitschr. 

 f. Elektrochem., p. 70. 1922; [Science 61 : 575-582. 1925I. 



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