FERMENTATIONS OF NITROGENOUS COMPOUNDS 69 



morphum can readily be obtained which convert glutamate 

 in the absence of oxygen to ammonia, carbon dioxide, 

 hydrogen, acetate, and several minor products which have 

 been identified as pyruvate, «-ketoglutarate, mesaconate, 

 and citramalate. 42 Mesaconate, which is a branched-chain 

 unsaturated dicarboxylic acid, was first detected by paper 

 chromatography as an acidic spot which also appeared as a 

 dark ("quenching") spot when viewed by ultraviolet light. 

 The characteristic ultraviolet quenching of mesaconate is 

 attributable to a conjugated system of double bonds in the 

 molecule. Subsequently both mesaconate and citramalate 

 were isolated in quantity and characterized more fully. 



A variety of enzymatic and tracer experiments have dem- 

 onstrated that mesaconate and citramalate are intermediates 

 in the fermentation of glutamate. As shown in Fig. 3, 

 glutamate is converted to mesaconate and ammonia, the 

 double bond of mesaconate is hydrated to give citramalate, 

 and citramalate is converted to pyruvate and acetate. The 

 formation of acetate, butyrate, carbon dioxide, and hydro- 

 gen from pyruvate presumably involves reactions of the 

 types discussed in Chapter 2. 



The formation of mesaconate from glutamate and its 

 further decomposition have been shown to occur at rates 

 as great as the over-all rate of glutamate fermentation by 

 cell-free extracts. Under conditions which block its hydra- 

 tion, mesaconate can be made to accumulate in almost 

 theoretical yield, i.e., 1 mole per mole of glutamate. The 

 formation of mesaconate from glutamate is of considerable 

 interest, because it involves the interconversion of straight- 

 and branched-chain compounds without loss of carbon 

 atoms. This process undoubtedly is the result of a fairly 

 complex reaction sequence, the details of which have not 

 yet been worked out. However, some information concern- 

 ing the origin of the methyl group of mesaconate has been 



