THE PROTEINS OF 3IICR0 -ORUANISMS 341 



-4H 



CHaCU.CUUH -r- XHo.UH > CH3.C— COOH > CH3.CH.XH2.COOH + H^O 



II 

 NOH 



Alternatively the keto-acid ma}^ take up an amino 

 group by transamination from another amino-acid : — 



CH3 



CH3CO.CO.NH.CH.COOH + XHo.CH.COOH — ^ 



"I 



(pyruvyl alanine) (a-amino-phenylacetic acid) 



I I 



(alanyl alanine) 



It has been suggested that the biological synthesis of 

 peptide chains from non-amino-acid precursors may 

 result from successive acylation and amination : — 



R.CO.COOH- 



Reduction of imine 



— ^ NH2 



Reduction of oxime | 

 > R.CH.COOH 



Transamination 



- R'CO.CO.NH.CH.COOH 



k 



Repetition 



R'CO.CO.NH.CH.COOH > R'CH.CO.NH.CH.COOH 



I of 1st step I I 



R XH2 R 



Continued repetition gives polypeptides and finally 

 proteins . 



Probably reactions of this type are only involved in 

 the synthesis of proteins from inorganic sources such as 

 in the growth of autotr()'j)liic bacteria or in the fixation 



