FRITZ LIPMANN 



hexose/2 *- ^^ph 

 ph-glyceraildehydc + ph 

 ph-glyceryl'^ph — 2 H —*■ '^ph 

 ph-glycerate — H2O 

 ph'^'enolpyruvate —*■ '^ph 



pyruvate -\r 1H 



lactate 



The terms '~ph, -ph, and ph characterize, respectively, the energy rich 

 phosphate bond (12 kcal.), the ester phosphate bond (3 kcal.) and inorganic 

 phosphate (7). 



Scheme i 

 The Process Pattern of Lactic Acid Fermentation 



HEXOSE 



* ^ , )k — r^ 



12 Kcal.(~ph) 

 ad 



12 Kcal.(~ph) 

 LACTIC ACID-^ 



The flow line represents a projection into space of the catalytic 

 pathway a hexose molecule travels to reach the inert end product, 

 lactic acid. Initial fission in the middle of the six-carbon chain seems 

 to be prompted by the introduction of phosphate groups at both ends. 

 This phosphorylation is a rather costly investment absorbing just one- 

 half of the gross yield of energy and thus reducing the net yield by 

 about fifty per cent. An initial investment of part of the ultimate 

 energy yield in the operation of the process is a notable feature. It is 

 this need of induction energy which makes the fermentative process 

 autocatalytic. The misleading statement is often made that, in fer- 

 mentation, one half of the hexose molecule oxidizes the other half, 

 suggesting a dismutative process. What happens, rather, is that a 

 hydrogen donor, after unloading of phosphate bond energy, is trans- 

 formed into a hydrogen acceptor. This manner of manipulation is 

 expressed in the characteristic shape of the flow lines which, in all 

 fermentations, fold back on themselves. The bending back, to accept 

 a pair of hydrogens released in a previous stage on the molecular flow 

 line, together with the initial expenditure of energy to start the process, 

 may be considered as general and dominant characteristics of anaerobic 

 metabolism. 



140 



