FERMENTATIONS OF NITROGENOUS COMPOUNDS 67 



The final products of the fermentation of glutamate by 

 CI. tetanomorphum are butyrate, acetate, carbon dioxide, 

 ammonia, and hydrogen. 39 These products suggest that 

 the terminal stages of the glutamate fermentation are sim- 

 ilar to those of the butyric acid fermentation of carbohy- 

 drates and other non-nitrogenous substrates. However, 

 one unusual and significant feature appears when the quan- 

 titative relations are considered, namely, only 1 mole of 

 carbon dioxide is formed per mole of glutamate decom- 

 posed. This is significant because in most organisms that 

 have been studied glutamate is converted to acetate via 

 a-ketoglutarate and the tricarboxylic acid cycle, and this 

 reaction sequence produces not 1 but 5 molecules of carbon 

 dioxide per molecule of glutamate decomposed; conse- 

 quently the observed yield of carbon dioxide excludes the 

 participation of the tricarboxylic acid cycle functioning 

 in the forward or oxidative direction in the glutamate 

 fermentation. 



In order to define the path of glutamate fermentation 

 more clearly, Wachsman investigated the fate of the indi- 

 vidual carbon atoms of glutamate by means of tracer experi- 

 ments. 40 Samples of glutamate labeled with C 14 in specific 

 positions were fermented by washed cells, and the products 

 were isolated and degraded to locate the isotope. Figure 2 

 summarizes the results. Carbon atoms 1 and 2 of glutamate 

 are converted mainly to acetate. Carbon atoms 3 and 4 

 are converted mainly to butyrate, carbon atom 3 appearing 

 in the a and y positions, and carbon atom 4 in the carboxyl 

 and ft positions; carbon atoms 3 and 4 also go to the methyl 

 and carboxyl positions of acetate to a small extent. Carbon 

 atom 5 of glutamate appears entirely in carbon dioxide. 

 These results show that two types of C 2 units are formed 

 from glutamate, one of which, derived from carbon atoms 

 1 and 2, is converted directly to acetate, whereas the other, 



