58 RESPIRATION 



1. Green plants, and unquestionably certain fungi also, if de- 

 prived of oxygen, respire anaerobicallv. 



2. Glucose and the enzyme complex, zymase, are universally 

 present in plant cells. 



3. Acetaldehyde as an intermediate product in the anaerobic 

 respiration of glucose has been detected in plant tissues. 



4. Alcohol, an anaerobic respiratory product, has been found 

 in higher plants and in certain fungi. Kostytchew (1908) found 

 that Agaricus cavipestris formed alcohol if the mycelium was sub- 

 merged, even in media lacking sugar. On the other hand, Asper- 

 gillus niger, grown in similar media, failed to produce alcohol. 



.Mechanism of aerobic respiration. The mechanism of aero- 

 bic respiration among fungi has been presumed to be like that 

 among green plants, and in neither group of plants have the de- 

 tails been fully substantiated. Palladin (1909) long ago postu- 

 lated a theory whose general plan outlined the mechanism as 

 follows: 



Intermediate 

 CeH 12 06 + Zymase — > anaerobic + 6H 2 + 12A 



products • Hydrogen acceptor, i.e., 



respiratory pigments, 

 cytochrome in fungi 



+ Dehydrogenase -* 6C0 2 + 12AH 2 



Reduced acceptor 



Then 



12AH 2 + 2 + Oxidase -► 12A + 12H 2 



This plan means, if elucidated, that after the intermediate an- 

 aerobic products are formed, they are oxidized by the active oxv- 

 gen that comes from the water molecules, and the freed hydrogen 

 combines with the respiratory pigments. As a next step, the 

 respiratory pigments in the presence of oxidase again acquire oxy- 

 gen, but they take it from the atmospheric oxygen. In this proc- 

 ess the sugar is completely oxidized, and the ratio of the volume 

 of CO;, released to the volume of O l . utilized is unity. 



.Mechanism of an akrobic respiration (alcoholic fermenta- 

 tion). Two theories have been propounded to explain the mech- 

 anism of alcoholic fermentation. One of these, called the pyruvic 

 acid theory, has been elaborated by Xeuber^ and his associates 

 [Xeuberg (1922), Neuberg and Gottschalk (1924)]; and the 

 other, commonly called the sugar-phosphate or the Harden theory 

 [Harden (1932)], by .Meyerhof and Kiessling (1935). 



