272 TEXTBOOK OF PLANT PHYSIOLOGY 



bacteria or the enzyme obtained from them. The theory of 

 anaerobic oxidation was worked out by Wieland, who showed 

 that it occurs at the expense of oxygen in the water molecule and 

 that methylene blue and similar compounds are not really oxidizers 

 but hydrogen acceptors, substances capable of uniting with the 

 hydrogen of water and liberating thus atomic oxygen, which pro- 

 duces oxidation proper. The enzymes hastening these processes 

 are not oxidases but reductases, substances binding hydrogen with 

 the hydrogen acceptors. 



Since, simultaneously with the reduction of the acceptors, the 

 reductases induce oxidation at the expense of the oxygen or more 

 exactly the hydroxyl group of water, it would be better to call 

 them, as suggested by Bach, oxydo-reductases, i.e., oxydo-reduct- 

 ive enzymes. An excellent example of such simultaneous oxidation 

 and reduction at the expense of the elements of water, is the reac- 

 tion of Cannizzaro which is produced by aldehydes in the presence 

 of alkalies: 



RCHO RCH2OH 



+ H 2 > 



RCHO RCOOH 



This reaction, as we have seen, plays an important role in the 

 process of alcoholic fermentation, and the mutase inducing it may 

 be added to the group of oxydo-reductases. 



On the basis of all these considerations, Palladin finally arrived 

 at the following mechanism of processes occurring during respira- 

 tion. First of all there occurs an anaerobic disintegration of both 

 the respiratory material and water, during which the carbon con- 

 tained in the respiratory material is oxidized to carbon dioxide 

 by oxygen of the water, the hydrogen acceptors (R) binding the 

 liberated hydrogen of the water molecule, 



CoHi 2 O fi + 6H2O + 12R = 6CO2 + 12RH 2 . 



The second phase consists of the oxidation to water of the 

 hydrogen bound by the acceptors. The liberation of the acceptors 

 permits them to resume their activity, 



12RH 2 + 6O2 = 12H 2 + 12R. 



By summing up both equations the usual formula for respira- 

 tion is obtained. 



