ALCOHOLIC FERMENTATION 87 



Presumably in vivo for glycogen synthesis the precursor of hexose-1-phosphate 

 is hexose-6-phosphate, formed from glucose by the action of hexokinase in the 

 presence of adenosine triphosphate as phosphate donator. In this case there is a 

 disappearance of free energy since the r-'ph group of ATP is transformed into the 

 energy-poor ester phosphate linkage. 



It should be noted that an explanation of the function of insuhn is that it inhibits 

 the effect of the anterior lobe of the pituitary gland which antagonises hexokinase, 

 hence stopping glucose phosphorylation and sugar utilisation in the usual glycolytic 

 chain (Cori, Colo wick, Himsworth, Young). 



MUSCULAR CONTRACTION 



Szent-Gyorgyi has prepared separate proteins from fresh muscle, actin and 

 myosin, which together form actomyosin. This reacts with ATP liberating inorganic 

 phosphate and setting free the energy of the r-^ph bond and providing the energy for 

 muscular contraction. Thus the whole of the glycogen breakdown chain has been 

 utilised to build up energy-rich phosphate bonds which are available immediately for 

 the energy of muscular contraction. For the regeneration of phosphate linkings the 

 whole glycolytic chain would be too slow for immediate action, but r^ph bonds are 

 stored in phosphagen which can immediately regenerate ATP from ADP. Meanwhile 

 glycolysis is set in motion for the regeneration of more r^ph bonds and the glycogen 

 is converted to lactic acid, which is carried back to the liver for resynthesis to glycogen 

 by a reversal of the glycol}i;ic chain of reactions. 



YEAST ALCOHOLIC FERMENTATION 



The process of alcohol production from glucose by yeast follows a course closely 

 similar to that of glycolysis, starting from glucose or maltose instead of glycogen ; 

 the initial phosphorylation requires hexokinase and ATP. Hexose-6-phosphate is 

 thus formed directly instead of through the intermediary of hexose-1-phosphate. 



The other difference from muscle glycolysis is at the end of the chain in the break- 

 down of pyruvic acid which, instead of being reduced to lactic acid, is first decarboxy- 

 lated to acetaldehyde (and CO 2) which is then reduced to alcohol. This reduction is 

 effected by alcohol dehydrogenase and is coupled with the oxidation of diphospho- 

 glyceraldehyde to diphosphoglyceric acid, whereby the coenzyme I reduced in the 

 latter reaction is reoxidised in the acetaldehyde reduction. The final reactions, 

 therefore, are : — 



Pyruvic acid -> Acetaldehyde + COg 

 Acetaldehyde + C0.I.2H -^ Ethyl alcohol + CO.I 



The energy changes are similar to those discussed in the case of muscle glycolysis. 



The flavour, bouquet and some of the physiological effects of alcohoHc drinks are 

 due in part to side reactions and to reactions involving nitrogenous materials from 

 the raw materials and yeast cells. 



