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as starting points for assimilatory processes in which the free energy 

 decreases. 



I cannot enter here into a discussion of the mechanism of this ATP 

 participation in assimilation. It may suffice to state that convincing 

 evidence for the co-operation of compounds with energy-rich phos- 

 phate bonds in the synthesis of carbohydrates, of fatty acids, of pep- 

 tides, of various methylated compounds and others has been obtained. 



I now wish to make a few remarks about the elementary reactions 

 which constitute assimilation. It has become increasingly clear that 

 in the chain of reactions which leads from the substrate to the assimi- 

 latory product we again encounter mainly both the transhydrogena- 

 tion and the transphosphorylation reactions, i.e., the transference of a 

 phosphate group from one molecule to a second, characteristic of 

 fermentation and respiration. But since so many divergent compounds 

 are present in the living cell it is not surprising that some other reaction 

 types are also present. We need only think of the more than twenty 

 amino-acids which are the building stones of all proteins, microbial 

 or otherwise. 



It is now certain that these can originate by the mechanism first 

 proposed by Knoop in which keto-acids together with NH 3 (as am- 

 monium ion) may yield an amino-acid with the intermediate forma- 

 tion of an imino-acid. 



R • CO • COOH+NHg +± R • COHNH 2 • COOH 



tl 

 RCHNH 2 COOH^±R.C = NHCOOH+H 2 

 2H 



The investigations of Braunstein have shown that at least certain 

 amino-acids may originate from the interaction of a keto-acid with 

 a second amino-acid according to the reaction: 



R' • CHNH 2 • COOH+ R" • CO • COOH <± 



«± R'COCOOH+R"CHNH 2 COOH 



This reaction type is usually designated as transamination, a. term 

 which might well be extended so as to include also the primary amino- 

 acid formation out of a keto-acid and ammonia. 



Very important work on the elucidation of the synthesis of the in- 

 dividual amino-acids has been done by Ehrensvard and his co-workers 

 in Stockholm who have performed an amino-acid analysis of the pro- 



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