SELECTED PAPERS 



interesting because it clearly represents another successful intervention 

 of a compound with an energy-rich phosphate bond. We owe to Lip- 

 mann the important observation that the conversion of pyruvic acid 

 by bacterial systems into acetic and formic acid is not, as had long 

 been accepted, a reaction in which water takes part, but a phosphor- 

 olysis, in so far that the primary product besides the formic acid is not 

 acetic acid but acetylphosphate. By adding formic acid with labelled 

 carbon to the medium it has been definitely proved that owing to the 

 high potential of the acetylphosphate this primary reaction is revers- 

 ible, and since Bacterium coli is also able to form formic acid out of car- 

 bon dioxide and hydrogen it is now quite certain that carbon dioxide 

 can also enter the metabolism via a synthesis of pyruvic acid. 



I cannot dismiss the subject of heterotrophic carbon dioxide assim- 

 ilation without leaving for a moment the microbiological field, and 

 asking your attention for analogous studies made in animal metab- 

 olism. Here in some cases it has been possible to trace the path which 

 the labelled carbon follows in the intricate web of metabolic processes. 

 Amongst others this has led to the startling observation that part of the 

 labelled carbon injected intraperitoneally in the form of a sodium bi- 

 carbonate solution into fasted rats can within a short time at least part- 

 ly be found back in the liver glycogen. And Wood and his coworkers 

 have even succeeded in bringing experimental proof that this labelled 

 carbon is located in the positions 3 and 4 of the glucose molecules 

 which are the building stones of the glycogen. This result is so gratify- 

 ing because it is exactly what might be expected on the basis of the 

 current reaction schemes in the supposition that glycogen synthesis 

 proceeds as the reversal of glycolysis. 



Finally it should be observed that in the last three years the use of 

 the stable carbon isotope has found application far beyond the prob- 

 lem of carbon dioxide assimilation. Werkman has succeeded in pre- 

 paring various acids, such as acetic, lactic, propionic and butyric 

 acids, containing heavy carbon atoms either in the carboxyl groups, 

 or also in other locations in the molecules. By adding such compounds 

 to the usual fermentation media of various types of bacteria they have 

 been able to trace conversions of these molecules which conversions 

 had at least partly a quite unexpected character. 



For the moment the number of these observations is still relatively 

 small, but they suffice to show that until shortly the metabolic capac- 



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