164 BREAKDOWN OF NITROGENOUS MATERIAL 



but, with one exception, such a reaction has not been demon- 

 strated in bacteria. A claim has been made that aspartic 

 acid is hydrolytically deaminated to malic acid by Ps, 

 fluorescens liquefaciens : 

 HOOC.CH2.CHNH2.COOH + H2O 



> HOOC.CH2.CHOH.COOH + NH3. 



The evidence for the reaction is not direct and requires con- 

 firmation with a cell-free enzyme system. 



Aspartic acid 



Since aspartic acid is oxidatively deaminated to oxalacetic 

 acid by Haemophilus influenzae, it provides an example of a 

 substrate which can be deaminated in the four ways so far 

 discussed : 



HOOC . CH2 . CO . COOH HOOC . CH2 . CH2 . COOH 



Oxidative \ deamination Reductivey^ deamination 



{H. Influ\enzae) /(Strict aerobes) 



HOOC . CH2 . CHNHo . COOH 



Desaturation /^ deamination Hydrolytic -v deamination 



1/ (Aspartase) {Ps. \ fluorescens) 



HOOC . CH = CH . COOH HOOC . CH2 . CHOH . COOH 



Dehydration deamination 



There is one particular example of this type of deamination 

 and that is the breakdown of L-serine by Esch. coli; the 

 postulated course of the breakdown is as follows : — 



CH3 



^C=0 +NH3 



COOH 



The experimental fact is that serine is attacked anaerobically 

 to liberate pyruvic acid and ammonia. To explain this 

 reaction the above steps have been postulated, starting with a 

 dehydration of serine to the unsaturated amino-acid by an 

 enzyme called " serine dehydrase." Preparations of washed 



