RESPIRATION AND FERMENTATION 273 



It is evident that according to this theory all of the carbon di- 

 oxide formed during respiration is of anaerobic origin, being formed 

 without the participation of oxygen of the air. The oxygen given 

 off during respiration as carbon dioxide has no connection with 

 atmospheric oxygen. Moreover, it is used exclusively for the 

 combustion of hydrogen eliminated by the hydrogen acceptors 

 from the respiratory material. The main enzymes of respiration 

 are not oxidases, but reductases, serving in the transmission of 

 hydrogen from the respiration material to the respiratory chromo- 

 gens. 



Palladin's ideas have found important corroboration in the 

 experiments of Oparin. The latter has succeeded in obtaining in 

 pure form a respiratory chromogen which is rather common in 

 plants, namely, chlorogenic acid, a polyatomic phenol derivative. 

 Being oxidized by atmospheric oxygen, which process takes place 

 very readily in the presence of a special oxidase, this compound 

 becomes a respiratory pigment, i.e., a greenish-colored, energetic 

 acceptor of hydrogen. If an amino acid is added to the solution, 

 it will be oxidized by the oxygen of the water molecule, and 

 the pigment will be transformed by the hydrogen to chlorogenic 

 acid. This reaction can be accelerated considerably in the pres- 

 ence of the oxydo-reductase found in large quantities in the sap of 

 sunflower seedlings. Thus, Oparin was able to reproduce arti- 

 ficially the respiratory process of plants: oxidation of the chro- 

 mogen by means of oxidase into a pigment, and its reduction to 

 chromogen by means of oxydo-reductase, with simultaneous oxida- 

 tion of the respiratory material, in the case given, an amino acid, 

 at the expense of the oxygen of water. 



With further action of oxidase on the respiratory pigment, a 

 deeper oxidation of the latter into a dark-brown, very stable sub- 

 stance takes place. This pigment cannot be reduced by hydrogen 

 and is therefore entirely inactive ; hence, it is necessary to take con- 

 centrations of oxidase and oxydo-reductase in which the oxidation 

 processes proceeding in the solution are balanced, in order to secure 

 a regular oxidation of the respiratory material. With an excess of 

 oxidase, the chlorogenic acid rapidly assumes the form of a brown, 

 inactive pigment and the reaction stops. 



Similar phenomena are observed in the plant cell. Under 

 normal conditions the oxidation and reduction processes are in 

 perfect harmony, and the combustion of the respiratory material,. 



