MICROBIAL METABOLISM AND ITS INDUSTRIAL IMPLICATIONS 



terns of Torulopsis utilis after this yeast had been grown in a medium 

 containing an ammonium salt and sodium acetate in which the two 

 carbon atoms had been labelled with the C 13 and C 14 isotopes respec- 

 tively. Their results agree with the hypothesis that the keto-acids oc- 

 curring in the tricarboxylic acid-cycle are either directly or indirectly 

 involved in the synthesis of several of the amino-acids. 



As for the synthesis of fatty acids, we have learnt from the impor- 

 tant investigations of Lipmann and of Barker that a transfer of the 

 acetyl group present in acetyl phosphate plays an important role. 

 Several arguments favour the primary reaction: 



CH 3 -COO' + CH 3 -COOP0 3 "^CH 3 -CO-CH 2 -COO'+HOP0 3 '' 



This type of reaction which repeats itself in the synthesis of higher 

 fatty acids can aptly be designated as transacetylation. 



Finally, we owe to the work of Challenger - and as far as animal 

 metabolism is concerned especially to that of Du Vigneaud - the know- 

 ledge that in the synthesis of several other biologically important 

 compounds a transfer of methyl groups, or in other words a trans- 

 methylation, is an essential step. 



A typical reaction of this type is the reaction between choline and 

 homocysteine which leads to the formation of dimethylamino-ethanol 

 and methionine according to the equation: 



(H 3 C) 3 N+ • CH 2 • CH 2 OH+HS • CH 2 • CH 2 • CHNH 2 • COOH 



tl 

 (H 3 C) 2 N+H • CH 2 • CH 2 OH+H 3 C • S • CH 2 • CH 2 • CHNH 2 • COOH 



We may conclude from the foregoing that, although the riddles of the 

 superchemistry of assimilation are still far from being solved, all the 

 available evidence supports the idea that we are dealing here with 

 chains of primary reactions which all belong to one of the following 

 five categories: transhydrogenation, transphosphorylation, trans- 

 amination, transacetylation and transmethylation. 



Carbohydrates, fats and proteins are the main quantitative constitu- 

 ents of the microbial cell, and this makes one realize that micro- 

 organisms might at some time be used as human food or animal fodder, 

 the more so because the amazing synthetic capacity of many microbes 

 permits them to build up these pillars of animal nutrition, and especial- 

 ly the proteins, in a medium containing nothing but a single organic 

 compound together with some inorganic salts. Because of this, mi- 



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