202 III. OXIDATION AND METABOLISM 



creased in some tissues, and unchanged in others. 2,4-Dinitrophenol (DNP) 

 has been shown to enhance the respiration of Hver siHces metabolizing 

 octanoate and pyruvate; a greater proportion of acetoacetate was found 

 than was noted in control tissues.' ^^ Richter''-'' suggested that galactose 

 may have a specific effect upon the utilization of fat, since rats on a diet of 

 margarine plus galactose survived longer than did animals which received 

 only glucose with the fat. 



Choline also plays a role in determining the rate of fat oxidation. Thus, 

 Artom'-^''^'^ found that labeled palmitate or stearate was oxidized to a 

 lesser extent, as determined by the production of C^'*02, by liver slices of 

 rats previously maintained on a choUne-deficient diet than by slices of 

 livers of rats previously on a stock diet, or on a low-protein regimen which 

 was supplemented with choline. A high level of fat oxidation occurred in 

 liver slices from choline-deficient animals which had been given injections 

 of choline shortly before death. Smce the in vitro addition of choline did 

 not effect a similar stimulation in the rate of fat oxidation, it is suggested 

 that the enhancement of fatty acid oxidation is not due to free choline but 

 to some substance or substances formed from choline in vivo. 



The rate at which octanoic acid-l-C^^ is oxidized in vitro has been shown 

 to be related to the inorganic salts in the medium. Geyer and co-workers''^^ 

 reported that the rate of metabolism of this acid in rat liver slices was 

 greatly increased when potassium or lithium salts were added to the 

 medium at the expense of the sodium salts. The increase was reflected 

 principally in the increased acetoacetate production. In the case of rat 

 kidney slices, potassium stimulated the metabolism of octanoate, but 

 lithium did not. 



Vestling and co-workers'-'* demonstrated that leukemic liver systems are 

 incapable of normal fatty acid oxidation. It is beUeved that the presence of 

 malignant leucocytes in the liver leads to a failure in at least one important 

 enzyme system. 



It is Hkewise obvious that the rate of fat oxidation, particularly in the 

 case of fasting animals or of those on a limited supply of calories, is regu- 

 lated by the expenditure of energy. Under these conditions, fat calories 



7" p. Fantl, G. J. Lincoln, and J. F. Nelson, Biochem. J., 48, 96-99 (1951). 



720 C. P. Richter, Science, 108, 449-450 (1948). 



"1 C. Artom, Federation Proc, 12, 171-172 (1953). 



"2C. Artom, J. Biol. Chem., 205, 101-111 (1953). 



7" R. p. Geyer, M. F. Meadows, L. D. Marshall, and M. S. Gongaware, J. Biol. Chem., 

 205, 81-85 (1953). 



"^ C. S. Vestling, S. Kaufman, R. E. Maxwell, and H. Quastler, J. Biol. Chem., 165, 

 385-386 (1946). 



