GLYCEROL 43 



4. The Disposition of Newly Synthesized Fatty Acids 



The fate of newly synthesized fatty acids has recently received much 

 attention.^^'^^'^^*"^^^ The incorporation of isotopic carbon from C^*- 

 labeled acetate was found to proceed more rapidly in the neutral fat of the 

 liver of the intact rat than in the phospholipid fraction. This indicated, 

 according to Pihl and Bloch,^^ that phosphoHpids are not obligatory inter- 

 mediates in fat synthesis. These results are at variance with those ob- 

 tained in the earlier studies of Barrett et al.,^^^ in which a higher proportion 

 of D-labeled fatty acids were found in the phospholipids of the liver than 

 in the neutral fat of this organ after deuterio-linseed oil had been fed. 

 According to the experiments of the former investigators,^^ in all the in- 

 ternal organs other than the liver, including mesenteric fat, the isotope 

 concentrations were found to be higher in the phospholipids than in the 

 neutral fat fraction. The distribution of biosynthesized fatty acids be- 

 tween the neutral fat and the phospholipid fractions was similar in fed 

 animals and in those fasted for as long as 72 hours. ^^^ The ratio between 

 these fractions varied only slightly from 1.0; in the intestine, however, the 

 phospholipid fatty acids were the more heavily labeled. Since the pro- 

 portionate ratio between the intramuscular and the subcutaneous fat dif- 

 fered, it was concluded that they represent separate types of hpid. The 

 neutral fat fatty acids of the intramuscular tissue were found to have a 

 higher activity than did those in the phospholipid fraction, whereas the 

 opposite situation obtained in the case of the subcutaneous tissue.^" 

 While the relative activities of the saturated and unsaturated fatty acids of 

 fed and of fasted rats were similar in the liver, in the case of the carcass 

 fat, the saturated fatty acids were found to be more heavily labeled when 

 the animals had been fasted. ^^^ Moreover, Bloch^ reported that acetate 

 carbon is incorporated at a much faster rate into saturated than into 

 unsaturated acids by rat liver slices. 



5. The Biosynthesis of Glycerol 



Because of the close relationship between glycerol and glucose, both 

 from a structural and from a metabolic standpoint, the synthesis of the 



'9* G. EhrUch and H. Waelsch, /. Biol. Chem., 163, 195-202 (1946). 



>«P. V. Harper, ^Y. B. Neal, Jr., and G. R. Hlavacek, Metabolism, 2, 69-80 (1953). 



"« J. T. Van Bruggen, T. T. Hutchens, C. K. Claycomb, and E. S. West, /. Biol. Chem., 

 ;?00, 31-37 (1953). 



"'J. G. Coniglio, C. E. Anderson, and C. S. Robinson, Am. J. Physiol, 177, 69-72 

 (1954). 



"8H. M. Barrett, C. H. Best, and J. H. Ridout, /. Physiol, 93, 367-381 (1938). 



