30 Introduction 



VIII. Fermentation (2) 



If Arthur Harden 14 is right, that the oxido-reduction offer mentations is the main 

 reaction of fermentations because by the oxidation-reduction the meaning of the 

 fermentations is fulfilled, then 1939 was the year the chemical mechanism of fer- 

 mentations was discovered. In 1939 at Dahlem the chemical reactions were dis- 

 covered 15 by which triosephosphate is oxidized to pyruvic acid and pyruvic acid 

 is reduced to lactic acid : 



(I) 3-Phosphoglyceraldehyde + H3PO4 =^ 1,3-diphosphoglyceraldehyde 



(II) 1,3-Diphosphoglyceraldehyde + DPN ^ 1,3-diphosphoglyceric acid DPNHo 



(III) 3-Phosphoglyceraldehyde + H3PO4 r DPN = 



(Balance) 1,3-Diphosphoglyceric acid -f DPNHo 



1,3-Diphosphoglyceric acid is then dephosphorylated by ADP (adenosine diphos- 

 phate) to pyruvic acid, and the latter is hydrogenated to lactic acid by the 

 DPNHo formed in reaction (II). All these reactions occur in vitro upon addition 

 of the pure Substrate and the crystallized enzymes to one another. 



1,3-Diphosphoglyceraldehyde is the only one of these Compounds which we 

 did not isolate, because 1,3-diphosphoglyceraldehyde in aqueous Solution hydro- 

 lyzes to 3-phosphoglyceraldehyde and H3PO4. Thus, in the entire chemical 

 mechanism of fermentations, there remained in 1939 one single sustance about 

 which it was possible to quarrel. 



Therefore began the long argument about 1,3-diphosphoglyceraldehyde. 

 Meyerhof initiated the fight in 1943 and Lipmann and many distinguished 

 biochemists followed suit. Because the question at issue — the mechanism of fer- 

 mentations — was a biochemical problem that had resisted Solution for a hundred 

 years, the course of this controversy may be described. 



The fact that needed explanation was that 3-phosphoglyceraldehyde was dehy- 

 drogenated only in the presence of phosphate and that, after dehydrogenation, 

 the added phosphoric acid turned up in the 1-position of the 3-phosphoglyceric 

 acid. No one could come to any conclusion other than that the aldehyde was first 

 phosphorylated in the 1-position 



R R 



C<^ + H3PO4 5* C^OH 

 ^O X OP0 3 H 2 



and that the aldehydic group was subsequently dehydrogenated to a carboxyl 

 group by means of DPN (disphosphopyridine nucleotide). Because of earlier 

 experimental results, this Interpretation Struck us as particularly plausible. In 

 purely chemical experiments we had found 16 that the aldehyde group of the gly- 

 ceraldehyde is activated by the addition of phosphate to the neutral aqueous Solu- 

 tion without enzymes to such a degree that it is oxidized to the carboxyl group by 

 molecular oxygen. Dorothy Needham 17 later made the Observation that DPN can 

 replace the oxygen in this reaction. Thus, in the chemical model DPN actually de- 

 hydrogenates glyceraldehyde, if phosphate is added to the neutral aqueous Solution. 



