NITROGEN METABOLISM 229 



CHa CH, +2H CHa— CH2 



I I I I 



(Ho CH.COOH " " 



NH NH2 



(proline) (w-iniino-valeric acid) 



Anaerobic conditions are essential, and bacteria are 



particularly active in effecting this type of breakdown, 



although yeasts and moulds are also capable of it. Almost 



all amino-acids are liable to reductive deamination. 



(6) Hydrolytic to give a-Hydroxy-acids, 



H2O 

 R.CH2.CH.NH2.COOH ^ R.CH2.CHOH.COOH + NH3. 



The products are substituted lactic acids ; indole -lactic 



acid from tryptophane, and phenyl-lactic acid from 



phenylalanine are examples : — 



CH2.CH.XH2.COOH CH2.CHOH.cuoH 



I 



O'lienylalanine) (phenvl-Iactic acid) 



Different bacteria may attack different optical isomers ; 

 thus Proteus destroys ^Z-tyrosine and leaves the Isevo- 

 isomer and produces the cZ-hydroxy-acid, whilst B. 

 syhtilis attacks the Isevo -isomer and leaves (/-tyrosine 

 unharmed, the product being the Z-hydroxy-acid. 

 CHo.CH.XH2.COOH 

 /\" 



I I > i I ^ ^^^3 



OH OH 



(tyrosine) (p-hydroxyphenjl-lactic acid) 



(c) Desaturative to give Unsaturated Acids, 



R..CH2.CH.NH2.COOH > R.CH=CH.COOH + NH3. 



The a- [i linkage is attacked wdth formation of substituted 

 acrylic acids. This type of breakdown is observed with 

 the coli-typhoid group of organisms. As examples may 

 be quoted the formation of fumaric acid from aspartic 

 acid : — 



