ENERGY SUPPLY OF THE CELL 69 



III. THE ROLE OF OXYGEN IN ALL FERMENTATIONS 



Hydrogen and oxygen are chemical contrasts to a 

 larger degree than any other two elements. Oxidation 

 and reduction are diametrically opposed reactions; 

 dehydrogenation means oxidation; reduction means 

 either the addition of hydrogen, or the removal of oxygen. 



In organic compounds, hydrogen is not as conspicuous 

 as oxygen. There are usually a number of hydrogen 

 atoms, only a few of which can be easily activated. 

 If an oxygen atom is present in an organic compound, 

 it marks reactivity, a step away from the '^parum 

 affinis'^ of the inert hydrocarbons. Thus we have 

 come to consider oxygen as an indicator of biochemical 

 usefulness. The degree of usefulness of a substance 

 for a certain organism is dependent upon the number 

 of oxygen atoms as well as their position in the molecule. 



Aside from this, the role of oxygen in respiration, 

 the abundance of oxygen in the air, the ubiquity of it 

 make it appear of paramount importance in life processes. 

 Even though the basis of all oxidations and reductions 

 may be the change of hydrogen atoms, we notice such 

 reactions primarily through their counterpart, oxygen. 

 There is no need, as far as the author can see, to eliminate 

 the word oxidation from our biochemical vocabulary. 



The primary purpose of fermentation is apparently 

 the energy supply of the ce^. It is brought about in 

 practically all cases by oxido-reductions. The one 

 outstanding exception is the urea fermentation which 

 must probably be classified as ^ hydrolysis. Hydrolyses, 

 as a rule, yield so little energy that they cannot be used as 

 source of energy by organisms. (See however p. 76.) 



In all oxido-reductions, some hydrogen is removed 

 from the substrate, and is placed in the hydrogen 



