EVALUATION OF METABOLIC PATHWAYS 55 



pentose cycle 



Gluconate-6-P > fructose-6-P 



major 



7^ > F-1, 6-diP -^ glycolysis + TCA cycle 



Fructose-6-P \ 



\^ minor 



> G-6-P -^ pentose cycle 



This conclusion is dra\vn from the consideration that the 

 fructose-6-P derived from the labeled gluconate should 

 bear the following labeling patterns (1) (see also Fig. 2.2): 



1 C 1 CO2 



+ 

 2C 2C 2222 



3 3 3 3 

 3C-^6 3C ->2233+C44 

 6 4444C55 



4G 4C 5555 C66 



6 6 6 6 



5C 5C 



6 C 6 C 4 F-6-P + 2 triose-P 



Further catabolism of F-6-P may be predicted as follows. 

 Let us consider the fate of gluconate-C-2: 



In Table 2.2, data are provided on the total recoveries 

 of C^^Oo from individual carbon atoms of glucose and 

 gluconate. For gluconate, the maximum fraction decar- 

 boxylated is 88%. This represents the maximum amount 

 of pentose phosphate that could have traversed the cycle, 

 and the probable actual amount that did so. 



According to the scheme just presented, the re-formed 

 fructose-P (from gluconate) will have the original C-2 from 

 gluconate in carbons A and C (1 and 3). Sixty-seven per 

 cent of this will be in carbon A, 33% in carbon C. 



