H. A. BARKER 



Other reduced. This is true in sugar fermentations by lactic acid 

 bacteria which produce glycerol. The dihydroxyacetonephos- 

 phate initially derived from carbons 1 to 3 of glucose presumably 

 is reduced, and the glyceraldehyde initially derived from carbons 

 4 to 6 is oxidized. 



A fermentation pattern more frequently encountered is that 

 in which part or all of the substrate, usually after some prepara- 

 tory reactions, is oxidized and then is transformed into an hydro- 

 gen acceptor. The simple lactic acid fermentation of glucose is 

 of this type; glyceraldehydephosphate is oxidized and the 

 product is converted to pyruvate, which is reduced to lactate. 

 A variation of this pattern is known to occur in two fermentations 

 in which the reduction precedes rather than follows the oxidation 

 in the path of substrate degradation. This situation is encoun- 

 tered in the fermentations of uric acid (30) and of orotic acid 

 (18). In the former, the first step is the reduction of uric acid 

 to xanthine, which is probably coupled with oxidation of glycine 

 and pyruvate derived from xanthine. In the orotic acid fer- 

 mentation, an initial reduction of orotic acid to dihydroorotic 

 acid is coupled with the oxidation of an as yet undetermined 

 compound. 



Besides the true fermentations just described, several other 

 closely related catabolic processes sometimes referred to as 

 "anaerobic oxidations" are utilized by anaerobic bacteria. 

 These processes are similar to the true fermentations in that they 

 provide energy for growth, and they frequently produce acids, 

 gases, and odors characteristic of fermentations. They differ 

 from true fermentations in that two major substrates are required, 

 one to serve as an oxidant, the other as a reductant. The latter 

 is usually an organic compound, although hydrogen gas and 

 carbon monoxide are used as reductants by some species. The 

 oxidant may be either an organic or an inorganic compound 

 according to the nature of the organism. The best known 

 example of the use of organic oxidants is in the so-called Stickland 

 reaction (23) catalyzed by Clostridium sporogenes and several other 

 Clostridia. In this reaction an amino acid such as alanine or 



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