I20 



E. S. GUZMAN BARRON 



Lactate 



The Multiple Pathway of Pyruvate Metabolism 



+H, +NH3 



^ Pyruvate '^ Alanine 



C4 



o 



Acetoacetate 



X 



+CO, 

 +H,0 



1 



Oxaloacetate 



Lactate + Acetate + COo 



Acetaldehyde + CO^ 



+ Pyruvate 



Acetylniethylcarbinol.+ 2 CO. 

 4-NH3 



Fat ^5±^ Acetate <*— ;• "Active" acetate + Oxaloacetate -=:i Aspartate — i ^ 



Citrate ^= Isocitrate 



O 



+ 

 Oxalosuccinate 



O 4 



4- 



Malate 

 O/f 



+ 

 Fumarate 



Protein 

 if 



i Glutamate 



of isocitric acid by isocitric dehydrogenase and triphosphopyridine 

 nucleotide (TPN) to oxalosuccinic acid and its decarboxylation to 

 a-ketoglutaric acid by a specific carboxylase has been demonstrated by 

 the beautiful experiments of Ochoa (67, 69). The other systems have 

 been known for some time. 



The interposition of enzymatic reversible oxidation-reduction systems 

 in the various steps during the burning of foodstuffs, already shown in 

 the scheme of pyruvate metabolism, allows the production of a series 

 of coupled reactions whose speed and direction will be determined not 

 only by the value of the equilibrium constants but also by the environ- 

 ment (temperature, O2 tension, CO2 tension, electrolytes, hormones, 

 etc.). 



