SATURATED FATTY ACIDS 17 



C'"* was the same following the administration of C'^-carboxylacetate and 

 a-C^^-pyruvate, and, on the other hand, after that of a-C^'*-acetate and 

 /3-C^ ''-pyruvate. In the first ease, the octanoic acid, which was synthesized, 

 was labeled on the odd carbons while, in the second case, the acid was 

 labeled on the even carbons. These results are supported by the findings of 

 Anker^^ that the carboxyl group of the acid synthesized after the feeding 

 of Q:-C'**-pyruvate has twice the concentration of isotope which obtains in 

 the whole molecule. Moreover, when the radio C is introduced into the 

 carboxyl group of pyruvic acid, it does not appear in newly synthesized 

 fat.*^ All these observations are in harmony with the concept that ace- 

 tate is the building stone for fatty acids, and that it arises from pyruvate 

 (and hence from carbohydrate) by decarboxylation of this keto acid. 

 Ponticorvo et al}^ demonstrated that 20 per cent of the isotopic carbon 

 fed as acetate was incorporated into the fatty acids of growing rats. 



{2) The Site of Biosynthesis of Fatty Acids from Acetate 



The liver has usually been considered to be the chief organ in which fat 

 synthesis takes place. Rittenberg and Bloch^'* were the first to demon- 

 strate that fatty acids could be synthesized in the liver from the acetate 

 building stones. The experiments of Pihl and Bloch^^ indicated that labeled 

 acetate was incorporated into the triglyceride fats in the isolated liver of 

 the rat; the rate at which acetate was incorporated into the triglycerides 

 was greater than that of its incorporation into the phospholipids. Chernick 

 and co-workers" likewise noted, on the basis of experiments with rat liver 

 slices, that fat synthesis from glucose occurs chiefly in the liver. Masoro 

 et al^^ confirmed the fact that the liver is the principal site of lipogenesis. 



However, in spite of the commanding role of the liver in fat synthesis, 

 this function can be assumed by many other tissues. Fat synthesis has 

 been demonstrated in surviving slices of rat kidney and diaphragm as well." 

 Labeled acetate is incorporated in the fatty acids in the mucosa of the gas- 

 trointestinal tract of rabbits.^^ The utilization of acetate is reported to be 

 especially marked in lung tissue. Chernick and associates^" showed that 

 rat arterial wall can effect a synthesis of fatty acids from acetate, as well 



"L. Ponticorvo, D. Rittenberg, and K. Bloch, /. Biol. Chem., 179, 839-842 (1949). 



6" A. Pihl and K. Bloch, /. Biol. Chem., 183, 431-439 (1950). 



6' S. S. Chernick, E. J. Masoro, and I. L. Chaikoff, Proc. Sac. Exptl. Biol. Med., 73, 

 348-352 (1950). 



58 E. J. Masoro, I. L. Chaikoff, and W. G. Dauben, /. Biol. Chem., 179, 1117-1125 

 (1949). 



" G. Popjdk and M. L. Beeckmans, Biochem. J., 47, 233-238 (1950). 



so S. S. Chernick, P. A. Srere, and I. L. Chaikoff, J. Biol. Chem., 179, 113-118 (1949). 



