232 IV. CONVERSION OF FAT TO CARBOHYDRATE 



workers^'^^ accounted for all the oxygen consumed by liver slices in the three 

 processes, deamination, carbon dioxide formation, and ketone body syn- 

 thesis. On the basis of these results, Stadie^^''' stated that "there was no 

 oxygen whatever available in the metabolism of the diabetic liver slice for 

 this conversion." Similar results were reported later by Stadie and his col- 

 laborators'^^-^^^ in liver slices of fasting, phlorhizinized rats. No gluconeo- 

 genesis attributable to fat could be shown by direct analyses in the case of 

 livers of diabetic cats. 



5. Resume of Current Hypotheses Regarding the Fat— ^-Carbohydrate 



Conversion 



One cannot categorically deny the possibility that fatty acid carbons may 

 be transferred to carbohydrate. However, as a result of the studies of a 

 number of investigators who employed isotopes, it is becoming certain that a 

 reaction of this nature is of minor importance. According to Buchanan and 

 co-workers,^^ the proportion of butyrate converted to carbohydrate was 

 less than 5% of the butyrate absorbed. In sharp contrast to this, Wier- 

 zuchowski and Ling''® calculated that the growing pig may convert over 

 50% of the ingested carbohydrate (starch) to fat. 



The earlier evidence of the non-convertibility of fatty acids to carbohy- 

 drate, based upon work carried out before isotope technics were available, 

 must still be accepted at face value. Experimental evidence which can be 

 adduced from studies on the amouat of liver and carcass glycogen follow- 

 ing the feeding of even-cham fatty acids or of natural fats can only be in- 

 terpreted as indicative of the failure of this transformation to occur to any 

 significant degree. Similarly, the data obtained by the employment of the 

 D:N ratio, the R.Q., or the use of epinephrine and insulin can best be ex- 

 plained by the non-transformation of fat to carbohydrate. 



On the other hand, no one doubts the ability of the glycerol moiety to 

 contribute to the tissue and liver carbohydrate. This change can readily 

 be demonstrated when glycerol is fed as such or in the form of triglyc- 

 eride molecules which are incapable of being stored. There is less evidence 

 for the synthesis of glucose from the glycerol moiety of the natural fats, al- 

 though most workers believe that the reaction does occur when natural fats 

 are oxidized. Fats having an odd number of carbons are likewise sources of 

 glucose to the extent that the fatty acids are convertible to propionic acid ; 



13* W. C. Stadie, J. A. Zapp, Jr., and F. D. W. Lukens, J. Biol. Chem., 132, 423-443 

 (1940). 



135 W. C. Stadie, J. Clin. Invest., 19, 843-861 (1940). 



136 M. Wierzuchowski and S. M. Ling, J. Biol. Chem., 64, 697-707 (1925). 



