Oxidative Pathways of Carbohydrate Metabolism 179 



Intracellular distribution of coenzymes 



The general finding that, in animal tissues and tumours, 

 DPN is present predominantly in the oxidized form whereas 

 TPN is almost exclusively in the reduced form (Clock and 

 McLean, 1955a), indicates that these coenzymes are relatively 

 inaccessible to each other. This suggests that they are either 

 largely bound to other cell constituents or located in different 

 cell compartments. 



The intracellular distribution of DPN+, DPNH, TPN+ and 

 TPNH in rat liver (Clock and McLean, 1956) is shown in 

 Table VI. It is of interest that the total TPN content of liver 



mitochondria accounts for approximately 36 per cent of the 

 total cellular TPN and is of the same order of magnitude as 

 the total DPN in the mitochondria. Much more of the total 

 DPN (75 per cent) than of the TPN (45 per cent) is present in 

 the soluble fraction. These results are slightly different from 

 those of Jacobson and Kaplan (1957) who found a smaller 

 proportion of the total DPN in the mitochondria. 



This work is now being extended to tumours and to the 

 liver of rats under different hormonal treatments. The intra- 

 cellular distribution of coenzymes will be of particular 

 interest in those conditions where marked changes in mito- 

 chondrial numbers and structure have been demonstrated. 



REFERENCES 



Abraham, S., Hill, R., and Chaikoff, I. L. (1955). Cancer Res., 15, 177. 

 Agranoff, B. W., and Brady, R. O. (1956). J. biol. Chem., 219, 211. 



