CHAPTER II 



PRIMING REACTIONS 



I. GLYCOLYSIS AND THE HEXOSEMONOPHOSPHATE 



SHUNT 



The name glycolysis is given to the sequence of enzymatic reactions 

 (Embden-Meyerhof scheme) which bring about the fragmentation of 

 carbohydrates by a pathway which does not involve the intervention of 

 oxygen molecules. The enzymatic system for glycolysis is a universal one, 

 at least in its main outlines, although there are numerous variations differ- 

 ing in certain details. 



The most completely understood system is that of the alcoholic fermen- 

 tation of glucose in the presence of yeast. 



A. Alcoholic Fermentation 



The fermentation of grape juice (pH around 5'0) under the influence of 

 yeasts growing on the surface of the grape (especially Saccharomyces 

 cerevisiae) and transported from one to another by insects (in particular 

 wasps), has been known since ancient times. The manufacture of beer and 

 of bread are further well-known examples of alcoholic fermentation, that 

 is the anaerobic breakdown of glucose with production of ethanol and COg. 

 It was Theodor Schwann who first showed, in 1837, that the alcoholic 

 fermentation of grape juice, at that time a phenomenon of some mystery, 

 depended on the introduction of living cells into the sweet solution. He 

 described yeast simultaneously with Cagniard-Latour. This great dis- 

 covery at once encountered the open opposition of the chemists. For them, 

 alcoholic fermentation was a simple chemical process, expressed by the 

 equation 



CeHiaOe ^ 2C2H5OH + ZCO^ 



Liebig even went so far as to draw up with Wohler, and to publish 

 anonymously in Annalen der Pharmacie, a facetious article ridiculing 

 Schwann's views and depicting yeast as a sort of infusoria eating sugar, 

 excreting alcohol from the digestive tract and COg from a bladder in the 

 shape of a bottle of champagne. Twenty years later, in 1860, Pasteur 

 confirmed the views of Schwann, and the "vitalist" theory of fermentation 

 triumphed. 



In 1897 Buchner, whilst preparing extracts of yeast for a therapeutic 



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