THE CHEMICAL PROCESSES IN PLANT RESPIRATION 1 29 



The hydrogen acceptors (chromogens) are thus completely 

 regenerated and could be used in the oxidation of new portions 

 of respiratory material. Thus according to Palladin, the 

 atmospheric oxygen oxidises only the labile hydrogen of the 

 respiratory pigments. This process, taking place through 

 the action of peroxidase, has nothing to do with the formation 

 of CO2. a view which corresponds entirely with the current idea 

 of the nature of the action of peroxidase. It has already been 

 pointed out that peroxidase preparations oxidise only phenol 

 groups. 



The assumption is certainly not precluded that the results 

 of the above mentioned experiments of Kostychev, in which 

 fermented sugar solutions develop CO2 after the addition of 

 peroxidase and hydrogen peroxide, are due to the presence in 

 fermented sugar solutions of not only the respiratory material 

 but also peculiar hydrogen acceptors. These results could be 

 explained by Palladin's scheme. 



Palladin has proven experimentally that the conversion of 

 respiratory chromogens into pigments involves the absorption 

 of oxygen from the surrounding air.^ The above mentioned 

 investigations of Wieland on acetic acid fermentation also favor 

 Palladin's theory. The following interesting discovery of 

 Oparin- can serve as a particularly clear illustration of Palladin's 

 theory. From sunflower seeds Oparin isolated a substance 

 which appears to be identical with chlorogenic acid and which 

 brings about the oxidative deaminization of amino acids entirely 

 in the sense of Palladin's scheme. The substance in question 

 is changed to a green pigment as a result of the oxidation of its 

 hydrogen. Chlorogenic acid CieHigOg is a Depsid and a constit- 

 uent part of the tannin known as caffetannic acid.^ Cafife- 

 tannic acid would thus be called a prochromogen. 



Palladin's theory is an important working hypothesis which 

 should be tested further. ' 



1 Palladin, W. und Z. Tolstoi, loc. cil. 



2 Oparin, A. Biochem. Z. 124: 90. 192 1. 



3 Freudenberg, K. Ber. d. chem. Ges. 53: 232. 1920; Freudenberg und E. VoUbrecht. 

 Z. f. physiol. Chem. 116: 2V7. 1921. 



< On this point cf. Thunberg. Skand. Arch. f. Physiol. 30: 285. 1913; Meyerhof. 

 Arch. ges. Physiol. 170: 367. 428. 1918; 175: 1919; Z. f. physiol. Chem. loi : 165. 1918; 

 102 : I. 1918. 

 9 



