EVALUATION OF METABOLIC PATHWAYS 31 



SPECIFIC ACTIVITY OF Ci^Q. 



In principle, a distinction among the pathways should 

 be easy with isotopic tracers. As shown in Fig. 2.1, if a 

 molecule of glucose tagged in carbon 1 undergoes glycolysis, 

 the carbon chain is split in half; carbons 3 and 4 of glucose 

 become the carboxyl group of pyruvate, carbons 2 and 5 

 become the carbonyl group, and carbons 1 and 6 the methyl 



® 

 CO2 



c® 1 C® 1 c® 



I i 



C 2 C 2 C 



I I I 



C 3 ^ Pentose C 3 Glycolysis C 



I cycle I 



C 4 C 4 C 



C 5 C 5 C 



C 6 C 6 C 



C CI c 



— I I 



C C 2 C 



i ' I 



C C 3 C 



I Pentose | Glycolysis 



9 cycle 9 ^ 



->■ 



C C 5 C 



C® C® 6 C® 



Fig. 2.1. Sketch of the routes of breakdown of glucose by glycolysis 

 and by phosphogluconate cleavage. 



