EVALUATION OF METABOLIC PATHWAYS 45 



Entner-Doudoroff pathway predominates, since the amounts 

 are essentially equal from C-1 and C-4 of glucose. This 

 is revealed in Fig. 2.8^^ since there is reported to be no 

 Krebs TCA cycle in this organism. There is therefore no 

 second phase after 1 RTU in which C14O2 is formed from 

 carbons 2 or 6, as in yeast. 



.8. Phosphogluconate cleavage, followed by the complete 

 pentose cycle, is seen in A. suhoxydans fFig. 2.8C). In this 

 curve, both interval and total yields are greatest from glu- 

 cose C-1, >C-2, >C-3,4, >C-6. This is precisely in accord- 

 ance with expectations. The greater yield of C-1 over 

 C-2 in the respiratory CO2 suggests that pentose cycle ac- 

 tivity is not as great as phosphogluconate cleavage; some 

 C-2 is evidently utilized in pentose that undergoes assimila- 

 tion. The Entner-Doudoroff route is ruled out because 

 of the high yield of CO2 from glucose C-2 (higher than 

 from C-4). If A. suhoxydans utilized the Entner-Doudoroff 

 pathway, and then diverted the triose formed (from carbons 

 4, 5, and 6) into hexose phosphate via aldolase condensation 

 and degraded the latter via the pentose cycle, the C^^Oo 

 would be fairly rich from carbon 6. C-2, however, would 

 be retained as acetate, since pyruvate is converted nearly 

 quantitatively to acetate in this organism (12). 



With these alternate pathways eliminated, the contribu- 

 tion of the pentose cycle to total glucose dissimilation in A. 

 suhoxydans can be estimated quantitatively with the use of 

 the cumulative recovery data of Table 2.1. Thus, in an oxy- 

 gen atmosphere, at 1 RTU, conversion of glucose to pentose 

 phosphate = C-1 recovery = 72%.- Pentose phosphate un- 

 dergoing cycling = C-2 recovery = 63% of glucose adminis- 

 tered (hence, (63 X 100)/72 = 88% of pentose formed). 



2 2-Ketogluconate accounted for all (28%) of the glucose that was 

 not converted to pentose in this experiment. 



