FERMENTATIONS OF NITROGENOUS COMPOUNDS 65 



The pathway of L-histidine decomposition in Pseudo- 

 monas fluoresceins 32 involves the following sequence: 



tt . . f . -NH 3tt +2H 2 0^ . . -NH 3 



L-Histidme — >■ Urocanate — > Formimmoglutamate — > 

 Formyl glutamate — > Formate + L-Glutamate 



Clostridium tetanomorphum carries out a similar 

 sequence of reactions with certain modifications (Fig. 1) . 

 Urocanate has been shown to be formed from histidine 

 and further decomposed by washed cells. 34 - 35 The evidence 

 for formiminoglutamate (formamidinoglutarate) is less con- 

 clusive, although possibly adequate. Both washed cells 

 and an acetone powder have been observed to convert histi- 

 dine to a compound which on alkaline hydrolysis yields 

 1 mole each of glutamate and formate and 2 moles of 

 ammonia; these products are known to be formed under 

 the same conditions from formiminoglutamate. When 

 chromatographed on paper the compound has the same 

 R ; as the formiminoglutamate formed enzymatically by 

 liver enzymes, and gives the same color with a nitroprusside- 

 ferricyanide reagent that reacts with the formimino group. 

 The enzymatic decomposition of formiminoglutamate has 

 been observed but has not been extensively investigated in 

 CI. tetanomorphum. Presumably this is a tetrahydrofolic 

 acid-dependent reaction as are the analogous reactions in 

 liver 36 and in CI. cylindrosporum. 37 The immediate prod- 

 ucts of formiminoglutamate decomposition have not been 

 determined. However, glutamate has been detected in 

 small amounts during the fermentation of histidine, and 

 formamide* accumulates as a major end product of the 

 fermentations of both histidine and urocanate. Tracer 

 experiments have demonstrated that formamide is formed 



* Formamide is also formed from histidine by Aerobacter aero- 

 genes.z* 



