CARBOHYDRATE METABOLIC PATHWAYS 81 



certain, but in vitro experiments have pointed to the in- 

 fluence of CO factors such as Mg- + , DPT, and pyridine nu- 

 cleotides. We have already discussed some of these in the 

 first lecture, where in A. siiboxydans normally all the 

 carbohydrate that is broken down to CO^ and H^O tra- 

 verses the pentose cycle; but if Dowex adsorption is used 

 to remove Mg, DPT, and the pyridine nucleotides, then 

 re-addition of DPN allows some glycolytic reactions to oc- 

 cur. In the developing foetus, Jolley et al. (29) have found 

 that increasing the concentration of TPN can greatly in- 

 crease the ratio of pentose cycle "traffic" to the glycolysis— 

 Krebs cycle route. Table 3.4 shows that the oxidation of 

 glucose carbon 1 compared to C-6 in pig foetus hearts is 

 increased more than ten-fold by adding extra TPN to 

 the medium. Although this effect is greatest with homog- 

 enates, where the influence of TPN might be expected to 

 be felt to a relatively larger extent, the effect has also been 

 demonstrated in w^hole perfused hearts; Table 3.5 describes 

 this, where added TPN directs a doubling of the normal 

 ratio of oxidation of C-1 compared to C-6. The effect 

 is specific for TPN, and for the oxidation on the first car- 

 bon, as may be seen from the table in experiments with 

 DPN. This effect of TPN on oxidation routes has also 

 been noted by Wenner and Weinhouse (64), w^orking with 

 rat liver systems. 



This last point gives rise to a third question: that of the 

 share of total cellular oxidations that may normally be 

 carried by the pentose cycle. This w^as discussed in Chap- 

 ter 2; it is apparently not a large figure in most organ- 

 isms, yet it is a significant amount. However, the reductive 

 pentose cycle may also be important, as is suggested by at 

 least three different experiments that are recorded in the 

 literature. 



