38 II. BIOSYNTHESIS 



shown to be an important factor in fat synthesis. Boxer and Stetten^^^ 

 were the first to prove that newly synthesized fatty acids are reduced by 

 restriction of the food intake. Thus, Medes and co-workers, ^^^ basing 

 their conclusions upon the behavior of tissue sUces of rats, found that 

 lipogenesis from acetate was greatly impaired by fasting or by undernutri- 

 tion. The highest rates of fatty acid synthesis from acetate were ob- 

 served in the tissues from rats which had previously been fasted or had 

 undergone food restriction, and which had then been heavily fed for some 

 time prior to the removal of the tissues. Although lipogenesis does occur 

 in extrahepatic tissues, Medes and her co-workers reported that the rates 

 of synthesis were considerably below those in the liver. Lyon, Masri, and 

 Chaikoff^^^ reported further experiments on the effect of the nutritional 

 state upon the rate of fat synthesis from acetate. Whereas 25% of the 

 acetate added to the liver shces from rats which had been fed ad libitum was 

 converted to fatty acids, and 25% was oxidized, the average recoveries of 

 fatty acids from the liver slices of rats fasted six, twelve, or eighteen hours 

 before sacrifice were only 25, 12, and 3%, respectively. The amount of ■ 

 acetate oxidized remained at figures varying between 20 and 30%. It is 

 suggested that the glycolytic and oxidative enzyme systems remained 

 intact in the fasted animals, while the ability to synthesize fat from ace- 

 tate had been lost, for the most part. The lipogenic ability was rapidly 

 restored when glucose was given orally. The administration of a casein 

 hydrolysate was also shown to stimulate lipogenesis, but to a lesser extent 

 than did glucose; the feeding of corn oil had no effect in restoring the 

 capacity to synthesize fats. Conigho and co-workers ^'^" observed marked 

 impairment of the fatty acid synthesis in the whole rat subjected to inani- 

 tion. Van Bruggen et al."^ also found about one-third less fatty acid syn- 

 thesis in rats fasted 120 hours than in unfasted animals. 



The effect of inanition on the synthesis of fatty acids from glucose is the 

 same as its effect on lipogenesis from acetate. Masoro et al. ^^^ also reported 

 that the conversion of C^Mabeled glucose to fatty acids was reduced by a 

 twenty-four-hour fast to 10% of that noted when a standard diet was 

 given, although the rate of oxidation to C'^02 was not altered. Likewise, 



16' G. E. Boxer and De W. Stetten, Jr., /. Biol. Chem., 153, 607-616 (1944). 



i«8 G. Medes, A. Thomas, and S. Weinhouse, J. Biol. Chem., 197, 181-191 (1952). 



168 1. Lyon, M. S. Masri, and I. L. Chaikoff, J. Biol. Chem., 186, 25-32 (1952). 



"» J. G. ConigUo, C. E. Anderson, and C. S. Robinson, /. Biol. Chem., 198, 525-532 

 (1952). 



"1 J. T. Van Bruggen, T. T. Hutchens, C. K. Claycomb, W. J. Cathy, and E. S. West, 

 /. Biol. Chem., 204, 389-394 (1952). 



"2E. J. Masoro, I. L. Chaikoflf, S. S. Chernick, and J. M. Felts, /. Biol. Chem., 185, 

 845-856 (1950). 



