230 BACTERIOLOGICAL CHEMISTRY 



CGOH.CHa.CH.NHs.COOH > COOH.CH=CH.COOH + NH3, 



(aspartic acid) (fumaric acid) 



and of iminazole-acrylic acid or urocanic acid from 



histidine : — 



CH =C— CH2.CH.NH2.COOH CH =C— CH =CH.COOH 



II II 



N NH > N NH + NH3 



CH CH 



(histidine) (iiiiinazole-acrylic acid or urocanic acid) 



(d) Oxidative to give a-Keto-acids, 

 . R.CH2.CH.NH2.COOH — > R.CH2.C0.C00H + NH3. 

 Here the products are substituted pyruvic acids. This 

 type of degradation is not easily detected since the 

 «-keto -acids are unstable and readily undergo further 

 breakdown, particularly under the action of yeasts. It 

 is favoured by aerobic conditions. 



The breakdown of Z-glutamic acid and Z-aspartic acid 

 by H. parainfluenzce to acetic acid, carbon dioxide and 

 ammonia follows this type of degradation, the steps 

 being «-ketoglutaric acid, succinic acid, fumaric acid, 

 malic acid, oxalacetic acid, pyruvic acid, acetaldehyde 

 and acetic acid from Z-glutamic acid and oxalacetic acid, 

 pyruvic acid, acetaldehyde and acetic acid from /-aspartic 

 acid. 



The hydrogen donating amino-acid in the " Stickland 

 reaction " (see p. 218) undergoes this type of breakdown. 

 Alanine, for instance, yields acetic acid, carbon dioxide 

 and ammonia : — 



H2O 

 CH3CH.NH2.COOH — > CH3.CO.COOH + NH3 + 2H 

 CH3CO.COOH — > CH3CH0 + CO2 

 CH3CH0 — > CH3COOH 



All the above types of deamination yield products 

 which have the same number of carbon atoms as the 

 original amino-acid. The «-keto -acids, owing to the 

 ease with Avhich they lose carbon dioxide by the action 

 of the enzyme carl)Oxylase (see Chapter XV), give rise 

 to a series of products with fewer carbon atoms than the 

 parent amino-acid, thus : — 



