20 NITROGEN METABOLISM 



Nisman and his colleagues therefore support Stickland's 

 concept of the reaction mechanism and they believe that 

 reactions «, h and c are catalysed by an L-amino-acid 

 oxidase [51], a keto acid oxidase [cf. 39] and an amino-acid 

 reductase respectively. There is a complete lack of know- 

 ledge concerning the mechanism by which an amino-acid is 

 reduced to a fatty acid (reaction c). Reaction a is inhibited 

 by KCN and secondary octyl alcohol, b by iodoacetate and 

 c by arsenite [47]. The growth of CI. sporogenes at the ex- 

 pense of energy derived from amino-acids is characterized 

 by the production of acetic acid together with isobutyric, 

 isovaleric and optically active valeric acids, derived respec- 

 tively from valine, leucine and isoleucine by the Stickland 

 reaction. On the other hand, owing to its inhibitory effect 

 on the Stickland reaction, the utilization of glucose as the 

 energy source yields only acetic and butyric acids [16]. 



Fermentation of amino-acids by other organisms [20] 



Certain organisms live anaerobically by the fermentation 

 of one particular organic nitrogen compound whilst others, 

 although not so specific, are restricted to the utilization of 

 a small number of chemically related compounds. These 

 organisms have usually been isolated by the enrichment 

 culture technique and the anaerobic incubation of a sample 

 of mud or soil in a medium containing an organic nitrogen 

 compound as the major source of carbon. In the event of the 

 organisms requiring certain growth factors, a small amount 

 of yeast extract is usually included in the medium after the 

 first transfer. 



The anaerobic cocci Diplococcus glycinophilus [11], Micro- 

 coccus anaerobius and M. variabilis [19] are specific for 

 glycine, and no other substance is readily metabolized unless 

 glycine is also present. If cultures of D. glycinophilus are not 

 shaken, the overall fermentation is expressed by: 



4NH2CH2COOH+2H20=4NH3+3CH3COOH+2COo 



The fermentation is not a simple dismutation involving the 

 oxidation of one molecule of glycine to CO 2 and NH3 and 

 the reduction of three molecules to acetic acid and NH3. 



